Formal community-based youth mentoring relationships (CBM) are a popular form of intervention worldwide in which caring, non-parental adult figures are matched with at-risk children  to promote development and health. Common models suggest that a close mentoring relationship is needed for the success of the intervention. However, it remains unclear which key relational processes and variables promote relationship quality to generate the most significant benefits. Using the PRISMA framework, 123 articles were identified as relevant for this review which explores the state of the literature on CBM relationships describing the main findings regarding the characteristics of the relationship and the mediating and moderating variables. An essential ingredient that consistently emerged for generating mentoring outcomes is characterized by feelings of support, sensitivity, and trust and accompanied by a purposeful approach to shaping the goals of the relationship. A balanced approach comprised of recreational, emotional, and catalyzing aspects has been reported as essential for mentoring success. Mentors’ positive attitudes toward underprivileged youth, maturity in terms of age and experience are essential in forging positive relationships. Mentees who have better relational histories and more positive personality traits exhibited higher relationship quality. However, data imply the possibility of addressing mentees from moderate risk status. Preliminary evidence on thriving as a mediating variable was found. Program practices, such as training, parental involvement, and matching based on perceived similarities and similar interests, emerged as important factors. Generating many research suggestions, the review identifies research questions and uncharted territories that require inquiry. Youth mentoring, defined as a special caring dyadic relationship between non-parental adults and their mentees that aims to promote young people’s personal and professional development, has been acknowledged as a vital asset for youth development ,2. UnderTo provide young people with a resource for development and social integration that is lacking in their natural social web, organized mentoring programs have promoted formal mentoring relationships, either in the community or in the school setting . In commd), from 0.18 to 0.21 in DuBois et al. [Approximately 4.5 million young people are involved in community-based-mentoring relationships in the U.S. alone ,13,14 ans et al. ,13 from s et al. , and 0.2s et al. .Many widely used models of youth mentoring adopt the underlying theoretical assumption that a close, interpersonal relationship between a mentor and mentee is critical to ensure the success of the mentoring relationship . In partRecently, the literature has begun to adopt a more positive developmental theory-based approach that shifts away from viewing young people as deficient and needing treatment to a more positive empowering framework ,23. RejeHowever, despite the recent surge in mentoring literature, considerable gaps remain in our understanding of which are the critical relational processes that generate lasting benefits for young people in CBM . AttainiThis overview extends previous efforts e.g., ,26,28), ,28, 26,2A comprehensive search of the literature published between January 2000 and April 2020 was conducted by the first author. Both computer-based and manual search methods were used to identify pertinent studies. The computerized databases utilized were PsychINFO, ERIC, PsycNET, PubMed, Scopus, and Web of Science. The search of each computerized database included the following terms and combinations of terms: “youth mentoring relationship,” “youth mentoring relationship + community-based mentoring,” “youth mentoring relationship + mentoring length,” “youth mentoring relationship + mentoring duration,” “youth mentoring relationship + relationship quality,” “youth mentoring relationship + per/early-match termination/early closure,” “youth mentoring relationship + mentors’/mentees’/protégés’ characteristics,” “youth mentoring relationship + relational/relationship characteristics,” and “youth mentoring relationship + culture/context/gender/sex/race and ethnicity,” These searches yielded 1308 full-text peer-reviewed articles, dissertations, research and technical reports, and book chapters written in English.The first author conducted the screening. Dilemmas were resolved through discussions with the second author. Both researchers are experts in the field of youth mentoring. Publications were included if they were qualitative or quantitative empirical studies, research reports, or meta-analyses and review articles dealing with formal one-to-one face-to-face community-based mentoring. In some cases, they were site-based. The mentor relationship could be either short-term (<12 months) or long-term (≥12 months), as well as applying multi-component programs, such as skills-group components. For the current review, we consider mentoring as comprising a one-on-one interaction between a non-parental adult figure and a specific younger person (aged 6–25) to promote positive outcomes for the latter through the relationship. In the first round of screening, 692 publications addressing natural mentoring, professional, peer/cross-age mentoring, academic mentoring, work/vocational mentoring, or those concentrating solely on school-based or group mentoring were excluded. In addition, specific mentoring interventions, such as mathematics, sports, and health interventions, were also excluded. We chose to include 15 studies that addressed both CBM and SBM and six multi-component programs, such as mentoring interventions that also included skills groups. This decision was taken out of the desire not to exclude pivotal meta-analyses in the field of youth mentoring  and given the scant findings that address the various aspects of the mentoring relationship. Next, 208 duplicate items were excluded. Subsequently, the studies underwent a second round of screening, which excluded 272 technical reports, toolkits and manuals, conceptual work, editorials and commentaries, book chapters, as well as articles focusing solely on mentoring effectiveness that did not treat the quality of the relationship, relationship duration, relationship intensity, types of provisions, activities, structure, or satisfaction. Similarly, we excluded studies addressing young people’s social support or social capital in general or studies concentrating only on young adults. These screening stages yielded 136 empirical studies . The selection flow, presented in Fifty (37%) of the 136 studies were conducted in the Big Brother Big Sister (BBBS) program setting. Of the identified studies, 12 studies were gender-based, concentrating on studying boys’ or girls’ experiences. Ten articles referred to both adolescents and young adults. Thirteen studies addressed special mentored populations . The aim of the study, the sample characteristics, the program characteristics, country, study design, main analyses, and main findings, all coded by the first author and the Ph.D. student, are presented in This section is structured according to the four posited research questions. First, the primary findings concerning the critical characteristics of the mentoring relationship are reviewed as they relate to mentoring outcomes. The second section discusses methodological and measurement approaches. Findings on the mediating processes are discussed in the third section. We conclude with the precursors and moderating variables reported to influence relationship quality. Aspects of mentor and mentee, as well as gender, culture, program practices, and match characteristics associated with the duration, quality, and satisfaction of the relationship, are cited. The conclusion proposes directions and topics for future research. Throughout the review, the state of the art is summarized and subjected to a critical lens  was significantly associated with youth greater competence in BBBSA . A recenFurthermore, mentors’ perceptions  and mentDosage of the mentoring intervention was also suggested as an important determinant of mentoring relationship quality and outcomes. Nevertheless, here, too, the findings regarding its effect on the mentoring outcomes are mixed. For instance, DuBois et al.’s meta-analyses ,13 indicQuality of the relationship: Core ingredients. Beyond issues of time, models evaluating mentoring success point to the relationship’s quality as the primary vehicle of change [f change . These mf change ,48. Mentf change , social f change . Menteesf change ,52,53,54f change , hope, sf change , active f change , generalf change , academif change , and futf change . Similarf change . Positivf change .Mentors’ and mentees’ perceived support was related to the duration of the relationship in BBBS of America . MenteesNevertheless, a critical limitation of some of these studies is that few included control groups or used reports from the same informant  on the quality of the relationship or the level of functioning, thus possibly creating shared method variance  and the Quality of Mentoring Relationship Engagement Scale (Q-MRES) . The G-MFuture studies should develop new scales that measure the contribution of mentors’ specific behaviors and practices with the assistance of a panel of experts and weighing them against other instruments assessing relationship dimensions across other types of close interactions. This kind of examination could help determine whether the superiority of the one-factor-solution stems from a phenomenon similar to the “common factor” or the “Dodo bird verdict,” underscoring the centrality of warmth, genuineness, and empathy in psychotherapy and the relatively scant empirical evidence as to the advantages of specific techniques over others .Theoretical and preliminary empirical endeavors have been made to identify processes inherent to mentoring relationships, focusing on associations between general relationship quality and mentee development. A prominent model of mentoring relationships is Rhodes et al.’s (2006) model of youth mentoring. Drawing on theories of parent-child, teacher-child, and peer relationships, the model posits that a close mentoring relationship stimulates three intertwined processes: (1) enhancement of social and emotional development; (2) improvement in cognitive functioning; and (3) promotion of positive identity development, all of which subsequently result in positive outcomes. Although  meta-anaRecent empirical efforts have posited that the five Cs  of Positive Youth Development and positive psychology constructs, such as optimism and hope, can serve as potential mediators between mentoring support and mentee outcomes . For exaIn a longitudinal study conducted in BBBS America , the parMentor characteristics. To maximize the potential of the mentoring relationship, researchers have sought to identify specific preexisting characteristics of mentors that are associated with the mentoring relationship quality and relationship length. These moderators include age, gender, early experience in helping relationships, confidence and self-efficacy with the mentor role, attitudes toward children, expectations and motivation, and general well-being.Age. The literature has pointed to some advantages of older mentors in long-term mentoring programs with or without a defined endpoint, although the findings are inconclusive. It should be noted that these studies varied in their sample size, reporters, and methodology, perhaps explaining these inconsistencies. Data on children from a 10-year longitudinal study revealed a small but significant positive correlation between mentor age and match length, indicating that older mentors had longer matches in U.S. mentoring programs [programs . Youngerprograms . Americaprograms . Howeverprograms . Likewisprograms .Personal attributes. Mentors’ confidence in the mentoring relationship and self-efficacy in the mentor’s role results in spending more time with the mentees [ mentees , as well mentees ,138,139. mentees ,13. Thes mentees , mentori mentees , and exp mentees . Mentors mentees . Convers mentees .Mentors in BBBS America who held mentees in positive regard and were capable of engaging authentically and empathically with them were more likely to facilitate the establishment of strong relationships ,117. In A few, albeit contradictory, findings have related to intrapersonal factors, such as personality traits, well-being and relational history, of mentors who participated in short-term programs, thus calling for further exploration. For example, higher mentor conscientiousness, extraversion, and agreeableness were associated with closer mentor-mentee alliances reported by mentors . MentorsIn contrast, mentors who reported having experienced higher levels of early life stress had mentees who reported greater satisfaction in the mentoring relationship and decreased relational anxiety . These fMentee characteristics. Mentors are not the sole actors in the mentoring interaction. Through reciprocal communication, mentees shape the mentoring relationship with their mentor. Mentee characteristics may be linked to the quality of the relationship or to the increased risk of premature termination, though much work remains to be done. To date, most studies have limited their attention to mentee background characteristics, such as age and risk status. Age. The ability and motivation of young people to forge close relationships with their mentors can vary as a function of their developmental status. Different developmental phases may accentuate various issues throughout the mentoring relationship. Nevertheless, most studies have addressed adolescence as a unitary stage, without differentiating it into phases . Findings from various American programs have indicated that mid-to late-elementary school-aged children and younger adolescents reported closer relationships with their mentors and tended to have more enduring matches than those characterizing older adolescents [lescents ,53,113. Risk status. Beyond age, mentees’ risk factors have been found to be associated with relationship dysfunction. For instance, family instability may increase the risk of early relationship termination by circumscribing the mentees’ ability to maintain continuous contact with their mentors, particularly in single-parent homes affected by higher than average rates of home moves or family environments characterized by intense conflict, drug use, and unsafe parenting [arenting . Young parenting .Children and adolescents with significant disruptions in their attachments to their primary caregivers  may find it a challenge to engage in mentoring relationships, thus placing these relationships at higher risk than relationships with young people who do not fall into these populations . AlthougThe presence of co-occurring risk factors may challenge the mentoring relationship’s sustainability and longevity, as suggested by some studies conducted in various mentoring programs with or without fixed ending points and duration across diverse programs. Risk factors in children have been thought to accumulate additively in a linear manner, such that low-risk exposure is associated with the most favorable outcomes, and high-risk exposure is associated with the worst outcomes. For example, in a study of 1310 children and adolescents, Herrera et al.  found thFinally, several risk factors stemming from the mentees’ environment were reported to be negatively associated with the quality of the mentoring relationship in a sample of 455 Americans: economic adversity, family stress, and peer difficulties, but surprisingly, not individual risk, such as academic or behavioral problems, and mental health concerns . LengthiWhereas the studies reviewed above point to a set of mentee risk circumstances as damaging to the mentoring process. However, DuBois et al.’s  meta-anaRelational history. Feelings of suspicion, skepticism, resistance, and difficulty opening up, manifested throughout the relationships rooted in the youth’s painful history with their attachment figures, may be reenacted in the mentoring relationship [tionship . Prelimitionship . Early mtionship ,111. In tionship  and a lotionship  and exhitionship .Male mentees who reported better relationships with their parents or guardians at baseline participated in matches that lasted at least one year in BBBS America . AmericaPersonality. There is a dearth of work examining the role of personality among mentees. However, findings from a short-term limited-time mentoring program in Israel suggest that mentees’ positive personality traits, such as extraversion, agreeableness, conscientiousness, and openness, were positively correlated with more positive expectations to emerge as a result of the mentoring. Agreeableness was also positively correlated with mentees’ perceived quality of the relationship in a short-term Israeli mentoring program [ program . Mentees program . Future Mentoring Dyad. Some of the factors shaping the mentoring relationship pertain to broader aspects of the mentoring dyad. These include culture, gender, program practices, and match characteristics.Culture. Although culture can affect the goals and practices of the relationship [tionship , researctionship ,158. Indtionship : China—Ctionship ,159; Rwationship ; UK—[107tionship ; and thetionship , with ontionship ,164,165.tionship ,164,165.tionship . De Wit tionship  comparedSeveral qualitative studies on asylum seekers in Sweden and Australia have underscored the culturally specific needs of mentees to feel safe and protected, the need for social support and social capital, and their strong desire to fit in and move forward with their lives . GarrawaRace and ethnicity. Theoretical writings [writings  and qualwritings ,107,170 writings  and whenwritings . Howeverwritings ,70,171. Gender. The mentoring relationship is likely to be experienced and established differently by female and male mentors and mentees. For instance, gender-based theories pertaining to mentoring suggest that girls generally exhibit a more favorable response to mentoring because they place a greater emphasis on contact-focused goals [ed goals ,172). Hoed goals .Empirically, the quantitative findings concerning the influence of mentors’ and mentees’ gender are mixed. Note that, as BBBS interventions usually avoid making cross-sex matches, almost no data are available regarding the effect of cross-sex versus same-sex matches. Mentors. Early match terminations are less frequent for male than for female mentors in American programs [programs ,113,154.Mentees. The findings on the duration of relationships for boys and girls are mixed. Whereas one study conducted in the context of BBBS America reported that girls’ relationships lasted significantly longer than those of boys [ of boys , this fi of boys . Further of boys ,41.Inconsistent findings for the quality of the relationship have also emerged. Whereas girls in long-term relationships in BBBS America and in the short-term mentoring program were more satisfied with the relationship and rated it as more helpful than did boys ,173, anoQualitative analyses conducted in BBBS America and Croatia and in a short-term mentoring program in the UK show that both male and female young people and male mentors had similar expectations for the relationship, mainly to engage in fun activities . InterviMatch characteristics. Although mentors’ and mentees’ similarity and perceived similarity in terms of fields of interest, temperament, personality traits, relational styles, and shared attitudes and values have been argued to be fundamental to the quality of the relationship and its outcomes, there is a striking dearth of research on similarity-based matching [matching  This absThe lack of research notwithstanding, several studies have offered support to the critical role of match characteristics. For instance, in Eby et al.’s  meta-anaProgram Practices. Program practices may influence the mentoring relationship incorporated within them [Guidance. Guidance is seen to be a key element accounting for the length and quality of the mentoring relationship [hin them ,175. In hin them  meta-anahin them , which ptionship . Mentorstionship . The amotionship ,141,177)tionship , mentoritionship ,179, andtionship  in diffetionship ,147. A qtionship . Anothertionship .Ties with parents and guardians. Parents’ and guardians’ support of mentoring can either facilitate or hinder the development and maintenance of the mentoring relationship [tionship . Evidenctionship . Similartionship . Mentor tionship . Likewistionship .Qualitative studies have provided insights into parents’ and guardians’ perceptions of their roles in the mentoring process. Parents described devoting substantial energies to cultivating their children’s mentor-mentee relationship, engaging in a range of roles, including mediator, coach, and collaborator ,183,184.The current review illustrates the theoretical and empirical efforts undertaken over the last twenty years to capture the nature of CBM relationships. It demonstrates the importance of a single robust relational factor that includes the correlated dimensions of support, sensitivity, and trust to promote mentoring outcomes. Furthermore, the review highlights the impact of a balanced relationship in terms of the emotional tone, activities, structure, and hierarchy and underscores the need to adopt a more purposeful or intentional approach to shaping the goals of the relationship. Qualitative findings have yielded a triple typology, comprising the recreational, emotional, and catalyzing aspects of the relationship, which need further conceptualization and operationalization. The effect of duration on mentoring outcomes and mentoring quality emerged as significant, especially for long-term mentoring relationships and for mentoring programs with no definite ending point. Concerning the participants’ characteristics, the findings point to the benefits of mentors’ maturity in terms of age, attitudes toward underprivileged youth, experience, and of a certain measure of vulnerability when forming empathic relationships. Furthermore, some evidence indicated the advantage of the conditional assumption . However, the review provides a certain optimism concerning the prospect of including mentees from various age groups and moderate risk status. Moreover, preliminary evidence on thriving and positive youth development as mediating variables may lead to a better understanding of the relationship’s course. Finally, the importance of training, parental involvement, and matching based on perceived similarities and similar interests emerged as important factors contributing to the quality of various types of mentoring relationships. The findings of the current review indicate a number of directions for further research. Specifically, considerable work is needed to expand and translate the field’s theoretical foundation and the qualitative findings into measurable concepts. For example, adopting concepts from the field of psychotherapy and parenting, such as the “common factor,” “transference and countertransference,” “self-disclosure” , and “paFurthermore, the findings point to the need to probe the dynamics involved in mentoring and, in particular, the reciprocal influences between mentors and mentees, as well as processes of moderation and mediation. Moreover, to identify the mediating variables that shape the transactional nature of the mentor-mentee relationship more longitudinal data are needed from randomized control research designs that employ dyadic analyses, process models that take into account multiple individual and environmental characteristics in the same model . ExperimMore fine-grained research is needed to shed light on the processes involved and the clear implications of the relationship at different developmental periods. For example, researchers could examine mentees across various developmental periods, as was done in natural mentoring , startinThe use of multiple informants  and multi-methods in future research would help avoid problems associated with shared method variance. Specifically, it would be useful to examine the similarities and differences in informants’ perceptions and investigate their origins ,187. To Using natural or laboratory-based observations of the dyadic interaction  can clarFinally, theoretically, the field of mentoring relationship can benefit from incorporating the notions of social justice, as well as critical and feminist thinking into mentoring relationships ,190,191.Several pragmatic recommendations for mentoring practitioners emerged from the current review. Recruitment and selection of mentors and mentees is a significant task of mentoring organizations. The current review implies the need to assess mentors’ emotional maturity, cultural sensitivity, empathy, and attitudes toward at-risk youth and their families. In addition, training mentors toward shaping mentoring relationships characterized by warmth and trust, while adopting a balanced position integrating relational, recreational and goal-oriented approaches, was found to be a necessity. To achieve these, it is important to provide ongoing training to help mentors cope with relational difficulties resulting from mentees’ past relational histories and high-risk situation, as well as maintaining the relationship if motivation declines. Maintaining mentoring longevity for long-term mentoring relationships also evolved as an essential practice. Matching mentors and mentees according to similar interests and lack of significant dissimilarities, and treating mentoring rematches cautiously also surfaced as implications. Finally, in early-termination cases, the review pinpointed the importance of encouraging mentors and mentees to close the relationship properly rather than allowing the relationship to dissolve without formal closure. Nevertheless, the complexity of the findings and their nuances calls for caution in translating the results into applied guidelines.Millions of children and adults are involved in CBM relationships worldwide. This review indicates that long enough, supportive, reliable, trustworthy, and balanced mentoring relationships in terms of goals, structure, and behaviors serve as building blocks in promoting mentees’ development and minimizing adversity. These aspects are conditioned by moderator factors, such as mentors’ and mentees’ characteristics, programs’ guidance, parental involvement, and match characteristics. The potential benefits of the mentoring relationship spotlights the need for more research in this field. More theoretical and methodical work is needed to broaden the conceptual perspective of the field and to identify the mediating processes and the measurement gaps within the theory and research. Despite these, the review provides support to the benefits of mentoring relationships providing practical implications of the reviewed work and suggestions for much needed future research.


The essential components involve: 1. an auxin-activated proton pump; 2. arabinogalactan glycoproteins (AGPs); 3. Ca2+ channels; 4. auxin-efflux “PIN” proteins. Typical pinball machines release pinballs that trigger various sound and visual effects. However, in plants, “proton pinballs” eject Ca2+ bound by paired glucuronic acid residues of numerous glycomodules in periplasmic AGP-Ca2+. Freed Ca2+ ions flow down the electrostatic gradient through open Ca2+ channels into the cytosol, thus activating numerous Ca2+-dependent activities. Clearly, cytosolic Ca2+ levels depend on the activity of the proton pump, the state of Ca2+ channels and the size of the periplasmic AGP-Ca2+ capacitor; proton pump activation is a major regulatory focal point tightly controlled by the supply of auxin. Auxin efflux carriers conveniently known as “PIN” proteins (null mutants are pin-shaped) pump auxin from cell to cell. Mechanosensitive Ca2+ channels and their activation by reactive oxygen species (ROS) are yet another factor regulating cytosolic Ca2+. Cell expansion also triggers proton pump/pinball activity by the mechanotransduction of wall stress via Hechtian adhesion, thus forming a Hechtian oscillator that underlies cycles of wall plasticity and oscillatory growth. Finally, the Ca2+ homeostasis of plants depends on cell surface external storage as a source of dynamic Ca2+, unlike the internal ER storage source of animals, where the added regulatory complexities ranging from vitamin D to parathormone contrast with the elegant simplicity of plant life. This paper summarizes a sixty-year Odyssey.Novel molecular pinball machines of the plasma membrane control cytosolic Ca Secondly, the proton pump generates protons; arguably, these eject Ca2+ from the plasma membrane with AGP-Ca2+ glycomodules as the immediate source of cytosolic Ca2+. Thirdly, auxin transport involves the efflux of anionic auxin into the wall at low pH where it is protonated and thus becomes neutral. That allows it to diffuse through the plasma membrane into the cytosol of an adjacent cell at a neutral pH, where it re-ionises for efflux and the polar transport of auxin against the concentration gradient [ATPase Hgradient ,41.2+ signalling. This reinterprets the “acid growth” hypothesis [2+ homeostasis is a new paradigm relevant throughout the Plant Kingdom from tropisms to phyllotaxis [Here, we connect an auxin-activated proton pump with AGPs and Capothesis . The hitllotaxis .2+ stoichiometrically [2+-binding enables peripheral cell surface AGPs to play a role in Ca2+ signalling that differs fundamentally from the endogenous Ca2+ storage of animal cells. Numerous previous observations of AGP localization and chemical properties throughout the literature are consistent with the new paradigm that unifies AGPs and Ca2+ homeostasis with the regulation of plant growth.Michael Jermyn (1975) demonstrated the ubiquity of AGPs (first known as beta lectins) in an impressive range of seed plants , suggesttrically . This pH2+ appeared in 1991; the wound response of Acacia senegal and its secretory product, gum Arabic, consists of polysaccharides and glycoproteins related to AGPs [2+. In the same year [w/w. These AGPs were hydroxyproline-rich, with a significant glucuronic acid content (~10%). However, the crucial connection between Hyp-glycosubstituents and the pH-dependent Ca2+ binding property of AGPs with Ca2+ homeostasis only appeared quite recently when a molecular model depicted paired glucuronic acid residues of a Hyp-glycomodule that bound Ca2+ in a molecular dynamics simulation, which was then confirmed through an in vitro assay [An early indication of a connection between AGPs and Ca to AGPs . Signifiame year , the anaro assay .2+ influx. This falsifiable hypothesis makes several testable predictions: AGP glucuronic acid is essential for growth.2+ binding.AGP glucuronic acid enables AGP-Ca2+ binding is the source of cytosolic Ca2+.AGP-Ca2+ channels facilitate its influx.Specific Ca2+.Auxin triggers a rapid increase in cytosolic Ca2+ waves are essential for root growth.CaAGP adaptation to salt stress also involves upregulation of their genes.The molecular pinball machine is a visual metaphor where “PIN” proteins trigger the machine by supplying auxin that activates the proton pump with the release of proton “pinballs” that initiate Ca2+ binding by AGPs [2+ binding by paired glucuronic acid residues of Hyp-AG glycomodules is the major source of dynamic cytosolic Ca2+. When theory predicts, experiments decide. Therefore, plants should exhibit defective Ca2+ homeostasis if they lack AGP–glucuronic acid residues . However, generating AGPs that lack glucuronic acid was a considerable experimental challenge fraught by the redundancy of multiple glucuronosyl transferases (GTGlcA) in the Arabidopsis GT14 family. Both Dupree’s [glcat14a/b/e triple mutant plants, while the complementary approach by Showalter’s group generated a glcat14a glcat14b glcat14c triple glcat CRISPR-Cas9 mutant line. Those benchmark papers describe how mutants generated AGPs that lacked glucuronic acid; their compelling evidence for the essential role of AGPs in Ca2+ homeostasis is as follows:Numerous other physiological predictions include tropisms and phyllotaxis . In vitr by AGPs  implied Dupree’s  and ShowDupree’s  groups r2+ binding was associated with profound developmental defects: trichome branching, suppressed growth phenotypes, decreased inflorescent stem length and a drastic decrease in progeny. Physiological defects included sterility, abnormal Ca2+ transients, the attenuation of Ca2+ wave propagation and decreased responses to ROS activation of Ca2+ channels in roots.Plants have a huge investment in AGPs represented by about 85 genes in the Arabidopsis genome. Two groups ,18 repor2+ binding by AGPs in vitro.AGPs isolated from triple glucuronosyl transferase knockouts contained significantly less glucuronidation, with a corresponding decrease in Ca2+ and further corroborated by [Earlier work  showed erated by ,18.2+ signals generate defined pH signatures in plants [2+ signal (aequorin blue fluorescence) “immediately” after the addition of an auxin activating the proton pump, i.e., within seconds, possibly involving the enhanced diffusion of protons along the surface of the membrane, hence their delayed escape from the membrane surface into the adjacent bulk phase [A report that cellular Can plants  presentsn plants  that auxlk phase .2+ homeostasis demands a finely balanced efflux evidenced by the fifteen Ca2+-ATPase pumps located in both the ER and plasma membrane of Arabidopsis [While the pinball machine and Hechtian oscillator emphasise influx, Cabidopsis .2+ homeostasis in roots. Using the fluorescent reporter R-GECO1, they observed organised cytosolic Ca2+ wave propagation at the inner and outer zones of wild-type roots. However, wave propagation was notably disorganized in glcat14a/b/e mutant roots. They extended these observations to the H2O2 activation of Ca2+ channels during growth that had been reported in a seminal paper [2O2 rapidly increased cytosolic Ca2+, particularly at the growing tip of wild-type roots. However, this increase was much less in glcat14a/b/e mutant roots , which xpansion  needs to2+ and so may account for salt-sensitive crop plants such as rice. On the other hand, salt-resistant plants typified by salt-marsh flora and marine seagrass raise the question of mechanism. AGPs are involved in two well-documented instances: firstly, AGP upregulation is a direct response to increased salt levels in plant cell suspension cultures [Zostera marina, have returned to a marine habitat [+ ions with Ca2+ ions? Some plants such as Zostera have adapted by increasing their glucuronic acid content [2+. With recent advances in genetic engineering in mind, the possibility of re-engineering AGPs to enhance salt-sensitive crop plants is apparent.An increasing sodium ion concentration competes with bound AGP-Cacultures ; secondl habitat . Zostera content , hence i2+ ions as key players [2+ signature that encodes specific developmental cues has become quite attractive. Some, such as [“involves one messenger with many translators” and is encoded in Ca2+-signalling systems by Ca2+-binding proteins with different Ca2+ affinities. This may enable cells to decode an initial Ca2+ signal to yield graded or nuanced responses. They also noted [2+-influx systems in plants but suggested that “Ca2+-influx mechanisms and components were still to be discovered”. The molecular pinball machine fills the gap as an essential component of Ca2+ signalling and homeostasis; in quiescent cells, auxin and Ca2+ trigger pinball activity. Thus, “PIN” proteins supply auxin that activates the proton pump to promote expansion growth. However, the Ca2+ signal depends not only on AGP-Ca2+ but also on Ca2+ channels activated by reactive oxygen species (ROS) [2+ [2+ and a more rigid wall. However, AGPs in muro with a higher affinity for Ca2+ than pectic carboxyls effectively scavenge pectate Ca2+. This results in negatively charged carboxyl ions such that pectin macromolecules then repel each other [2+. This may account for the effect of low pH increasing wall plasticity by dissociating calcium pectate Ca2+ ions that are then captured by AGPs. That resolves the acid growth paradox.Oscillatory growth implies that a biochemical oscillator regulates the process, with protons and Ca players . It also such as , suggestso noted  the appaes (ROS)  and strees (ROS) ,69,70 ofes (ROS)  covalentes (ROS)  began thes (ROS)  soften tes (ROS) . Underlyes (ROS) . Howeveres (ROS) , which ies (ROS) , not onles (ROS) , but alses (ROS)  and hydres (ROS)  were alwes (ROS) . AGPs reROS) [2+ . Thus, pch other  and thusch other  may also


Urticaria is a common group of dermatologic disorders characterized by hives. Solar urticaria and heat urticaria are two rare types of chronic inducible urticarias. Solar urticaria is triggered by exposure to sunlight or ultraviolet radiation. Heat urticaria is triggered by exposure or contact with a heat stimulus. A 63-year-old woman is described who has both solar urticaria and heat urticaria and the features of these chronic inducible urticarias are reviewed. The woman presented with urticarial lesions that appeared both after exposure to the sun and after cooking at a stove. Additional history revealed she was previously diagnosed with diabetes, hypertension, and thyroid disease. After sun exposure, a punch biopsy of both the affected skin, as well as the normal-appearing skin, was done. Correlation of the clinical history, cutaneous examination, and biopsy examination confirmed the diagnosis of solar urticaria. Treatment of the patient’s urticarias included histamine 1 (H1) and histamine 2 (H2) antihistamines. Her symptoms resolved and did not recur provided that she took the medication as prescribed. Management of chronic urticaria includes not only treatment of the current episode but also prevention of future recurring urticarial lesions. In addition to antihistamines, treatment may include omalizumab (Xolair®) injections for persistent urticaria. Solar urticaria is an IgE-mediated hypersensitivity. It presents as hives and is caused by ultraviolet radiation or, albeit less commonly, visible light (400 to 750 nanometers). Several classifications based on either the wavelength of ultraviolet radiation or associated allergens have been proposed -3. Heat urticaria results from contact with the responsible thermal source; mast cell activation and histamine release are postulated to be involved in the pathogenesis. Clinical presentations can include either immediate and localized lesions, immediate and generalized hives, or delayed onset of wheals -6. A woman with not only solar urticaria but also heat urticaria is described. The salient features of heat and solar urticaria are summarized. An approach to the management of urticaria is summarized.A 63-year-old woman with a past medical history of diabetes, hypertension, and hypothyroidism presented for evaluation of repeat episodes of an itchy rash on her body after exposure to the sun, as well as recurrent erythema on her abdomen that appeared each time she cooked at a stove. Both of her skin conditions had been present for at least three years. She provided a photograph of periumbilical erythematous hives on her abdomen that repeatedly developed when she would cook at the countertop stove Figure . Her curIn addition, she would develop hives not only in sun-exposed but also in sun-covered areas after being outside. To demonstrate the lesions, prior to a follow-up visit she stood outside in the parking lot for 15 minutes with her pants and sandals on. Extremely pruritic, erythematous urticarial lesions developed on both covered and exposed areas of her legs and arms Figure , 3. SkinMicroscopic examination of the lesional skin biopsy showed widening of the spaces between the collagen bundles, consistent with edema. In addition, occasional eosinophils were present not only in the dermal blood vessels but also in the dermis Figure . In contLaboratory studies were performed. These included a complete blood count, comprehensive metabolic panel, serum protein electrophoresis, thyroid-stimulating hormone, thyroxine, triiodothyronine as well as tests for complement components, DNA antibodies, HIV antibodies, rheumatoid factor, ribonucleic protein antibody, scleroderma-70 antibodies, Sjogren syndrome A antibody, Sjogren syndrome B antibody, Smith antibody, and thyroid antibodies (peroxidase). All of the studies were either negative or normal except for a blood urea nitrogen/creatinine ratio of 23 , creatinine level of 1.05 mg/dL , and thyroid peroxidase antibodies of 157 IU/mL . Correlation of the clinical history, pathologic changes, and laboratory studies established not only a diagnosis of solar urticaria but also heat urticaria. Her initial management included histamine 1 (H1) and histamine 2 (H2) antihistamines, specifically fexofenadine 180 milligrams and famotidine 20 milligrams in the morning, and hydroxyzine 10 milligrams and famotidine 20 milligrams in the evenings. She tolerated this therapeutic regimen without any adverse effects. A follow-up visit showed that all symptoms and lesions resolved and did not recur even with occasional exposure to sunlight when she took the medications as prescribed. However, any variance of treatment resulted in recurrence of her urticaria, specifically when going outside. She continues to be managed on her current therapy without any additional flares of urticaria.Urticaria is a common dermatologic condition characterized by pruritic, erythematous wheals; in addition, it can be accompanied by angioedema of the subcutaneous or interstitial tissue. Urticaria can be further classified into either acute or chronic types. Acute urticaria is characterized by lesions that occur for less than six weeks and commonly has precipitating triggers. Chronic urticaria is the persistence of lesions beyond six weeks and can be further classified into chronic idiopathic urticaria or chronic inducible urticaria ,8.The symptoms of chronic idiopathic  urticaria occur with no known cause. In contrast, chronic inducible urticaria is triggered in response to a specific physical or environmental stimulus. These stimuli include cold, exercise, heat, light, pressure, and vibration ,9. Chronic inducible urticaria can be further classified into either physical or non-physical urticarias. Physical urticarias include not only solar urticaria and heat urticaria, but also cold urticaria, delayed-pressure urticaria, dermographism, exercise-induced urticaria, and vibratory urticaria. Non-physical urticarias include aquagenic urticaria, cholinergic urticaria, and contact urticaria . Solar urticaria is a rare type of physical urticaria which is immunoglobulin E (IgE)-mediated. It typically presents with short-lasting, pruritic, erythematous patches and wheals that form approximately five to ten minutes after exposure to sunlight. Solar urticaria can also be associated with systemic manifestations, such as dizziness, headaches, nausea, syncope, wheezing, and rarely anaphylactic shock -3,10. Solar urticaria mainly affects women and most patients present between the ages of 20 to 40 years. The symptoms associated with solar urticaria can vary in severity and duration depending on the length of light exposure, the intensity of light, and location. Direct light exposure is required; however, in some patients, symptoms may occur even when exposed to light while wearing clothing, such as our patient ,2. The pathogenesis of solar urticaria remains to be definitively established. The specific wavelengths of light (action spectrum) that elicit an urticarial reaction varies in each patient. However, most of the urticarial reactions occur following exposure to ultraviolet radiation ranging from 280-500 nanometers ,2. Investigators have proposed that the urticaria-triggering action spectra induces a cutaneous chromophore to absorb the light. The photoproduct that is created then acts as a photoallergen. Subsequently, IgE antibodies produced to the photoallergen bind to mast cells, resulting in histamine release ,2. Originally, in 1963, six types of solar urticaria were named by determining not only the amount of energy needed to elicit an urticarial reaction with an ultraviolet light meter but also whether an intradermal injection of the patient’s serum into their own forearm prior to irradiation of the site (passive transfer) or into the forearm of a non-solar urticaria volunteer after irradiation of the site (reverse passive transfer) resulted in urticaria. The nanometer range of the action spectrum was from 285 to 500: 285 to 320 (Type I), 320 to 400 (Type II), 400 to 500 (Type III and Type IV), 280 to 500 (Type V), and 400 (Type VI). Passive transfer was present in patients with Type I and Type IV solar urticaria and reverse passive transfer was only observed in individuals with Type I solar urticaria. Patients with Type V solar urticaria were sensitive to multiple diffuse bands of radiation. Patients with Type VI solar urticaria had photosensitivity due to protoporphyrinemia, and urticarial lesions occurred upon exposure to radiation at 400 nanometers, which corresponds to the absorption peak of protoporphyrin IX . Subsequently, in 1989, solar urticaria was reclassified into two different types. Type I solar urticaria is caused by specific photoallergens present in solar urticaria patients against which IgE antibodies are directed. In contrast, Type II solar urticaria is caused by a nonspecific photoallergen - generated not only in patients with solar urticaria but also individuals without solar urticaria - that induces IgE-mediated immediate-type hypersensitivity . Fixed solar urticaria is an additional distinctive form of solar urticaria. It is characterized by repeated episodes of wheals that are localized to only specific skin sites for that individual. There are not any associated systemic symptoms in patients with fixed solar urticaria . Heat urticaria is a rare form of chronic inducible urticaria that is characterized by pruritic, erythematous, well-demarcated wheals that form after heat exposure. Associated systemic symptoms, such as headaches, nausea, tachycardia, vomiting, and weakness may occur. Heat urticaria most commonly occurs in women and the average age of onset is 20 to 45 years. The most common triggers are contact with warm objects or foods, exposure to the sun, hot air, and warm baths. The average reported threshold temperature for symptoms is 44 degrees Celsius . The pathogenesis of heat urticaria involves the activation of mast cells. Subsequently, there is a release of inflammatory mediators, such as histamine. However, the stimulus that causes the activation of mast cells remains to be determined ,6. Heat urticaria has been classified as either immediate onset or delayed onset. In immediate heat urticaria, the lesions are pruritic and appear within minutes and resolve within one to three hours. Heat urticaria can be either localized or generalized onset; in localized immediate heat urticaria, the lesions are limited to areas of the skin that came in direct contact with or was exposed to the heat stimulus. In generalized immediate heat urticaria, the lesions are diffuse and not limited to areas in contact with the heat stimulus ,6. Delayed onset heat urticaria is characterized by wheals that have a burning sensation and occur 30 minutes to two hours after heat contact and resolve within 12 to 14 hours. Delayed onset heat urticaria is a familial condition with an autosomal dominant inheritance and its initial observation is usually in children. In contrast, immediate heat urticaria typically presents in adult women and is not inherited ,6. The woman reported in this paper has both solar urticaria and heat urticaria. This is a unique presentation of multiple physical urticarias. In a comprehensive review of heat urticaria, the investigators noted 8% four of 50) of the patients with heat urticaria also experienced either cold urticaria or dermographism. They also observed that occasional episodes of generalized lesions of heat urticaria occurred after exposure to a general heat environment such as sun exposure in 50% (24 of 48) of the patients; however, the researchers were able to exclude solar urticaria in 12 of these patients when additional testing to ultraviolet A, ultraviolet B, and visible light did not result in urticarial lesions [0 of the The first-line treatment for urticaria is a non-sedating H1 antihistamine, such as bilastine, desloratadine, fexofenadine, levocetirizine, and loratadine. Antihistamines block the effect of histamine on either H1 or H2 receptors of endothelial or sensory nerve cells, which reduces the effect of mast cell mediators on target organs. If symptoms persist, the dosage of the H1 antihistamine can be increased by up to four times the standard dose ,15. After one to four weeks, if the symptoms are not controlled, an H2 antihistamine such as cimetidine or famotidine can be added. Another option would be to add a leukotriene antagonist, such as montelukast, to block mast cell release. Our patient was concurrently treated with both an H1 antihistamine and an H2 antihistamine; a sedating H1 antihistamine (hydroxyzine) was prescribed in the evening to enable sleep ,16. The management of chronic idiopathic urticaria may include corticosteroids. In addition to oral corticosteroids, other systemic agents such as dapsone or methotrexate can be used in severe cases of acute urticaria or chronic idiopathic urticaria. Intramuscular corticosteroids, such as triamcinolone acetonide, can be used to control episodic flares of urticaria; the injection should be made deep into a muscle, such as the gluteus maximus muscle located in the upper lateral quadrant of the buttock. However, the usage of oral or injected corticosteroids is not recommended for long-term use due to adverse effects; therefore, they should be tapered once symptoms are controlled ,15. More recently, omalizumab has been used for patients with chronic urticaria. Omalizumab is a monoclonal anti-IgE antibody that has been shown to be extremely effective for patients with chronic idiopathic urticaria, cholinergic urticaria, cold urticaria, and solar urticaria. Omalizumab is administered as a subcutaneous injection that is given once every four weeks ,16.Physical urticaria is a class of chronic inducible urticaria. Our patient had two subtypes of physical urticaria: solar urticaria and heat urticaria. Although individuals may develop multiple types of physical urticaria, we are not aware of another individual with this unique combination of physical urticarias. She was successfully managed with H1 and H2 antihistamines with clearing of the urticaria and prevention of new lesions as long as she maintained the recommended treatment. The diagnosis of a physical urticaria can often be suspected based on the clinical history; however, skin biopsy or laboratory testing or both may be helpful in establishing the diagnosis.


The Ca2+-deficient vines exhibited significant reductions in shoot length, shoot and trunk fresh weights, leaf area, chlorophyll, which eventually led to drooping, yellowing, and chlorosis of leaves. Roots were less dense and primarily dark and necrotic. Furthermore, their xylem vessels were small, polygonal, and appeared to be collapsed yet increased in number and developed lateral roots. Despite such alterations, the anatomical organization of leaves was not affected, yet they developed with more xylem vessels with thick walls and lignin in their mesophyll and vascular tissues. The chloroplasts in internodes’ chlorenchyma, phloem, and cambium underwent significant ultrastructural modifications. The concentrations of macro and micronutrients varied significantly among the roots, trunk, canes, and leaves, including the growth characteristics. These structural and growth modifications of calcium deficiency enable us to understand better the link between the symptoms and functions and for a holistic understanding of Ca2+ functionalities.This study characterized growth characteristics and cellular details employing microscopy techniques in hydroponically-grown Ca Arguably, in this context, none other than calcium (Ca2+), the third most abundant metal in nature, has been influential and distinguishable in many ways vis-à-vis the rest of the nutrients for many reasons3. For instance, it regulates almost all our bodily and plant functions by serving both as a nutrient and a messenger4. Despite its prominence and the tsunamic corpus of information accumulated over the years, its most explicit contribution to plant metabolism is yet to emerge5. The complex process of its uptake entailing transport pathways, their diverse absorption abilities, and the lack of its redistribution accounts for such ambiguity and it being an intractable element7. As a result, Ca2+ nutritional studies never yielded reliable results, leaving many obscurities in its role as an essential element6. Nevertheless, since it directed life to evolve and conserve by promoting and regulating metabolic functions, a strong socio-economical driving force to understand its precise function persists4.Next to water, the availability and plants’ ability to acquire soil mineral nutrients determine our sustainable development and global health2+ influences the growth and structure of plants, including their productivity7, we need to reveal how Ca2+ transport and function are integrated from the whole plant to the subcellular level in different species8. Progress in this endeavor requires in-depth characterization and fundamental understanding of the symptomatology of organs in different plants at the whole plant and cellular levels by conducting starvation studies under controlled conditions10. Unlike other nutrients12, the links between Ca2+ deficiency and its symptomatology in different organs, including the complex interaction among other nutrients in its absence in various crops, are paradoxical, hence the limited understanding of its functionality5. This conundrum ensues because tissue requirements for Ca2+ are genetically controlled, expressing at different extents13. Consequently, its levels vary with stages of growth, among and within plant species5, between monocots and dicots13, and among genotypes of the same species8. Such wide variations result in uneven distribution among and within the plant parts14, and heterogeneous storage across cell types15, causing Ca2+ deficiency symptoms to differ from organ to organ, species to species, and among different genotypes of the same species16.To gain a realistic understanding of how CaArabidopsis17, the logical course of action to account for such wide variations is to document Ca2+ deficiency-related responses by sifting through symptoms of various tissues at cellular levels in each species and genotype1. Symptoms, the purest, truest, and the most tangible form of physiological response in advance to a harmful stimulus caused by abiotic and biotic factors mirror the abnormal function reflecting its role in the structural décor and metabolism. Based on this portrayal, the symptomatology conceptualizes functional roles using the imagery of nutrient deficiency symptoms. Typically, mineral nutrient deficiency is predicted and rectified through foliar analysis followed by fertilization1. Concerning Ca2+, such remedial measures present a daunting task because of its unique properties18. Consequently, to better understand the physiological functionalities of Ca2+, it is necessary to utilize deficiency symptoms and structural modifications1. These visual imageries imbued with the ability to reveal physiological insights provide us with a global perspective of plant function specific to the concerned nutrient20. Thus, the most articulate approach to determine the decisive physiological roles of Ca2+ is to integrate the directness of symptomatology with growth characteristics. That is because linking nutrient deficiency symptoms with physiological functions offers the simplest yet wide-reaching means capable of explaining and predicting the Ca2+ status in crop plants with high genetic diversity1. Because of this reason, the Ca2+ deficiency symptoms, relatively appearing first and very early22, have been investigated23 and used as diagnostic criteria for plants and soils24. This knowledge is acutely needed, especially now to sustain plant productivity against climate-change-induced challenging conditions such as mineral stress, water scarceness, increased groundwater salinity, soil pests build-up, etc.5. Our recent paper10 has covered some of this information by examining the physiology and carbohydrate metabolism (enzymes involved in photosynthesis and sugar metabolism) in Ca2+-sufficient and Ca2+-deficient grapevines. This study aims to comprehend the Ca2+ deficiency symptomatology related to growth, nutrient distribution, and morpho-anatomical and ultrastructural alterations of root and shoot systems. We chose grapevine because of its global socio-economic impact25, grown under Ca2+-deficient soil conditions13.Given the challenge of deriving functional insights from the model plant, 2+-deficient vines with no difference in the stem diameter between Ca2+-sufficient and Ca2+-deficient vines  remained intact in the Cayma Fig. E. Despityma Fig. E. Anotheyma Fig. E. These yma Fig. F. They syma Fig. F. It is 2+-deficiency-induced significant increases in the levels of B in roots   Fig. A. Also, ots Fig. B. Both Cals Fig. . The cryots Fig. A, whereaots Fig. B. Primar2+ nutrition that remains a mystery is how it influences plants’ growth, structure, and productivity4. Consequently, Ca2+-deficiency disorders continue to blight the horticultural industry. To better understand the virtues of calcium nutrition, we need to understand how Ca2+ transport and function are integrated from the whole plant to the subcellular level in different species26. Against this backdrop, we present an in-depth characterization and fundamental understanding of organs’ symptomatology at the whole plant and cellular levels to enhance major fruit crops’ nutritional quality. Such information is necessary to understand the function and the mobility of Ca2+ at both the cellular and whole plant level, to further the understanding of signaling, and eventually to design more nutritional crop plants that are also more resilient to stress27.One of the crucial aspects of Ca2+ nutrition and its functions in plants’ growth and development being enigmatic3. Although occasionally, these concerns have been dealt with in different species7, such erratic and feeble attempts are not of much use in resolving such intermittently pursued issues. To move forward, we need a simple technique applicable to all plants envisaging Ca2+ activity in the cytosol and its distribution in different parts of the plant28. In this regard, examining symptomatology appears promising in gaining a piece of complete knowledge about Ca2+ functionality in different species.The conflicting results from various studies illustrate the complexity of Ca2+ is accumulated in the faster-growing organs such as the fruit, especially the leaves, after taking into the root system15. Consequently, both will be symptomatic in the absence of Ca2+, as observed in this study showing chlorosis , wherein Ca deficiency significantly decreased the fresh and dry weight of root, stem, and leaves30. The chlorosis is due to the disintegration of chloroplasts by starch accumulation32, given that Ca2+ is needed for exporting photosynthates out of leaves to other growing organs9. On the other hand, the reduced leaf area is associated with the altered morphology of mesophyll  cells leading to reduced photosynthesis in the Ca2+-deficient vines10. It does so by decreasing carboxylation efficiency, photosynthetic capacity, quantum yield33 and disrupting the PS II system29. Furthermore, since leaves are the source of photosynthates11 and Ca2+ promotes cell elongation and cell division3, the reduced capacity of Ca2+-deficient leaves resulted in inhibition of shoot length and leaf area. Conversely, stem diameter did not differ  stems and roots that showed no variation in their internal structure between Ca2+-deficient and Ca2+-sufficient plants40. More specifically, the Ca2+-sufficient cambium cells developed dense cytoplasm  plants, reflecting calcium's enzymatic role in the meristematic regions of the plants. As opposed to stem diameter, the shoot length  disoriented and destroyed due to large starch granules10. Regardless, the ultimate result of chloroplast destruction is chlorosis10, which explains the Ca2+ deficient vines’ chlorotic leaves  cuttings, uniform in size, were self-grown in hydroponic containers for 6 wk in a glasshouse at 22 °C:18 °C with 16 h:8 h photoperiod. This study complied with relevant institutional and national guidelines. The water utilized for the hydroponic system was ultra-pure grade water , which had no (0 mM) calcium. The substrate in the containers included perlites washed with ultra-pure grade water three to four times before potting the grapevines. All grapevines were irrigated with ultra-pure grade water until the treatments were imposed. The glasshouse was located at Shanghai Jiaotong University, Eastern China . All vines were provided with macro-and micro-nutrients using a modified aerated Hoagland solution  containing 15 mM N (Ca(NO3)2·4H2O 4, KNO3 6, NH4H2PO4 1, (NH4)6Mo7O24·4H2O 0.1), 1 mM P (NH4H2PO4), 6 mM K (KNO3), 4 mM Ca (Ca(NO3)2·4H2O), 2 mM Mg (MgSO4·7H2O), 2 mM S (MgSO4·7H2O), 0.11 mM Fe (Na2Fe-EDTA), 0.05 mM B (H3BO3), 0.01 mM Mn (MnCl2·4H2O), 0.77 μM Zn (ZnSO4·7H2O), 0.31 μM Cu (CuSO4·5H2O), 0.1 μM Mo (NH4)6Mo7O24·4H2O) at pH 5.7–6.0 and renewed every 3 days. The respective salts of each nutrient are shown in parenthesis. Ca (NO3)2 was used as a source of calcium in the Hoagland solution for generating Ca2+ sufficient vines, which had a concentration of 4 mM. On the other hand, the Ca2+ starved grapevines were applied with NH4NO3 (4 mM) instead of Ca(NO3) in the Hoagland solution (NO3) to maintain the ionic balance as well as to induce calcium deficiency as per the studies by Volk et al. (2002)63. The experiment was conducted in a randomized block design, lasting for 52 days. Each treatment consisted of 12 vines, and the measurements were made on 6 plants.One-year-old homogenously rooted Thompson seedless grapevine 4. Nonetheless, its deficiency causes a severe reduction in the growth and development of plants, including the death of the plants, and the symptomatology varies from species to species, and plants have no adaptive mechanisms to calcium deficiency, unlike other nutrients such as potassium64. Consequently, calcium-deficient plants suffer the most21.The choice of no calcium and sufficient calcium was based on our preliminary experiments, which showed that of all nutrients, a lack of calcium led to the death of the vines. The deficiency of other nutrients induced physiological disorders. That is because calcium regulates almost all our bodily and plant functions by serving both as a nutrient and a messenger2+ deficiency and Ca2+ sufficiency. Leaf area was measured 52 DAT (days after treatment) using an LI-3000A leaf area scanner . More specifically, only the midvein length was measured at weekly intervals to measure the leaf area during the experiment. After that, at 52 DAT, the leaves were sampled to scan the leaf areas, and a linear regression equation was used to compute the leaf areas for the whole experiment. Since grapevine leaves attain maximum physiological activity at 40 days of age and start to decline at about 52 days65, we lasted the experiment to 52 days. Chlorophyll was measured using a SPAD-502 chlorophyll meter .The shoot length and diameter were measured weekly 10 days after imposing the treatments, i.e., Ca66, the N content was determined by Kjeltec 2300 Analyzer . The P, K, Ca, Mg, Fe, Zn, B, Cu, Mn content were measured by ICP-AES .Six vines were separated into root, trunk, cane, stem, and leaf at 52 DAT for each treatment. The separated parts were oven-dried to constant weight in an oven at 80 C and ground for nutrient analysis. According to the Kjeldahl digestion method2+ deficient and sufficient vines using a razor blade and fixed in FAA . Samples were vacuumed 1 h and stored at 4 °C until the samples were further processed using the microwave paraffin technique67. Before embedding, all steps entailing fixation were performed at 75 °C in a water bath. The fixative in the vial was replaced twice with a new pre-chilled solution for 2 min each time. The fixed samples were dehydrated with 60% ethanol for 2 min for dehydration, followed by 50% ethanol and 50% Tert-butanol for 2 min. For infiltration, the samples were first treated with 100% Tert-butanol for 7–8 min and then 50% Tert-butanol/50% paraffin for 2 min. Subsequently, the specimens were microwaved in 100% paraffin wax for 7.5 min and embedded and cooled to room temperature. After cooling, the paraffin blocks were sliced at eight μm and placed on a slide warmer at 48 °C for 24–48 h. The sections were stained with double staining of Safranine T and fast green. When staining was complete, a drop of mounting medium  was used to affix coverslips to the slides. Slides were placed under a compound microscope  attached with a digital camera to capture digital images, and the anatomical measurements were performed using the cellSens imaging software platform.Several small pieces of roots and leaf sections (1 × 1 cm) were cut from mid-laminar areas of Ca61 was adopted to examine the leaf ultrastructure. To examine the leaf ultrastructure, several 0.5 cm × 0.5 cm pieces were cut from mid-laminar areas of both leaves, using a razor blade, fixed in 0.25% glutaraldehyde in 0.2 M sodium phosphate buffer at pH 7.0. Samples were vacuumed for 1 h and stored overnight at 4 °C. The fixed tissues were washed with 0.1 M phosphate buffer and post-fixed in 2% OsO4 for 4–6 h at 4 °C. The leaf samples were dehydrated in a series of ethanol and acetone and embedded in the epoxy resin Epon-812. Ultra-thin sections (50—70 nm) transverse sections were cut with a glass knife and mounted on 200-mesh copper grids. The leaf sections were then double-stained with 2% uranyl acetate and 2.6% lead citrate and examined under a transmission electron microscope  (TEM) at 120 kV.The method described by Xie et al. (2009)t test. The data were analyzed using SPSS  statistical package.All data were subjected to analysis of variance (ANOVA). Significant differences (P < 0.05) between means were determined using a


In other terms, these cues are both causes and effects of clock molecular activation (recursion). Recently, we demonstrated that Ca2+ and Vm transitions during AP cycles in single SAN cells isolated from mice, guinea pigs, rabbits, and humans are self-similar (obey a power law) and are also self-similar to trans-species AP firing intervals (APFIs) of these cells in vitro, to heart rate in vivo, and to body mass. Neurotransmitter stimulation of β-adrenergic receptor or cholinergic receptor–initiated signaling in SAN cells modulates their AP firing rate and rhythm by impacting on the degree to which SAN clocks couple to each other, creating the broad physiologic range of SAN cell mean APFIs and firing interval variabilities. Here we show that Ca2+ and Vm domain kinetic transitions (time to AP ignition in diastole and 90% AP recovery) occurring within given AP, the mean APFIs, and APFI variabilities within the time series of APs in 230 individual SAN cells are self-similar (obey power laws). In other terms, these long-range correlations inform on self-similar distributions of order among SAN cells across the entire broad physiologic range of SAN APFIs, regardless of whether autonomic receptors of these cells are stimulated or not and regardless of the type (adrenergic or cholinergic) of autonomic receptor stimulation. These long-range correlations among distributions of Ca2+ and Vm kinetic functions that regulate SAN cell clock coupling during each AP cycle in different individual, isolated SAN cells not in contact with each other. Our numerical model simulations further extended our perspectives to the molecular scale and demonstrated that many ion currents also behave self-similar across autonomic states. Thus, to ensure rapid flexibility of AP firing rates in response to different types and degrees of autonomic input, nature “did not reinvent molecular wheels within the coupled-clock system of pacemaker cells,” but differentially engaged or scaled the kinetics of gears that regulate the rate and rhythm at which the “wheels spin” in a given autonomic input context.Ca The heart is a central player within a hierarchical system of clocks operating within the autonomic neurovisceral axis that creates and synchronizes rhythmic functions ranging from milliseconds to days and beyond . The hea2+ via a criticality mechanism  that generates cyclic AMP (cAMP), leading to modulation of cAMP-gated ion channels, exchange protein directly activated by cAMP (EPAC) signaling, and protein kinase A (PKA) and Calcium/calmodulin-dependent protein kinase II (CaMKII)-dependent kinase activities, mechanisms that regulate intracellular Ca2+ levels, Ca2+ dynamics and membrane potential within SAN cells , and the extent to which Vm and Ca2+ become coupled during AP cycles in any given epoch. For more details, see The SAN cell coupled-clock system comprised a calcium “clock,” the sarcoplasmic reticulum (SR), which continuously oscillates Caechanism  and phasechanism ; the Ca2echanism . The criechanism . The “biAN cells . Variablin vitro, of SAN tissue ex vivo, or of heartbeat intervals in vivo  of isolated SAN cells  in vivo  indicate2+ and Vm domain transitions during APs are cues, which not only regulate activation states of clock molecules, but are also regulated by the activation status of the very molecules they regulate. In other terms, changes in these cues cause changes in clock molecule activation that feed back to change the characteristics of activation cues. This recursive dynamic imparts robustness to SAN cell automaticity (2+ and membrane clock molecules couple to each other throughout AP cycles is due to transitions (changes) that occur in Ca2+ and Vm domain cues throughout AP cycles (These time-dependent Camaticity . The varP cycles .2+ and Vm domains that emerge during the spontaneous diastolic depolarization (DD) phase of an AP cycle have been conceptualized as the AP “ignition phase”  that self-organize to form Ca2+ wavelets that propagate locally , resulting in Ca2+ influx that contributes to the further organization of the ensemble LCR Ca2+ signal via feed-forward electrochemical (Ca2+–Vm–Ca2+) signaling, when the diastolic Vm enters a range that cues the activation of L-type Ca2+ channels (Cav1.2). The ignition phase of the coupled-Ca2+ and Vm domain subcellular kinetic transitions culminates in the generation of cell-wide events; a marked transition in the rate of Vm depolarization, due to the activation of Cav1.2, results in the rapid AP upstroke and Ca2+ influx, which, via Ca2+-induced Ca2+ release from the SR via RyRs, generates an AP-induced cytosolic Ca2+ transient (CaT). In other terms, spontaneous, cell-wide Ca2+ signals and APs in SAN cells emerge from spatiotemporal self-organization of spontaneous subcellular Ca2+ oscillations   . SERCA2aSpatiotemporal self-organization across geometric scales (subcellular to cell-wide) is a manifestation of criticality that has been observed in excitable cells throughout nature  includin2+ signals (cues) generated by the Ca2+ clock within isolated SAN cells to the cell surface membrane proteins during APs to elicit a change in Vm manifests long-range power law correlations (are self-similar) across species (2+ and Vm domain kinetic transitions (cues) during AP cycles in single SAN cells isolated from mice, guinea pigs, rabbits, and humans are self-similar to each other during APS and self-similar to trans-species APFIs of these cells in vitro, to heart rate in vivo, and to body mass (It has recently been discovered that coupling of subcellular Ca species . Specifiody mass .2+ domain) and limit-cycle (Vm domain) mechanisms couple to each other during AP cycles (Neurotransmitter stimulation of β-adrenergic receptor stimulation (βAR) or cholinergic receptor (CR)–initiated signaling modulates the AP firing rate and rhythm of SAN cells by impacting on coupled-clock protein functions, modulating the degree to which criticality (CaP cycles . APFIs iP cycles .Vm and Ca2+ domain cues during the diastolic AP ignition (Vm and Ca2+ cues in other cells during CRs and during βARs and (2) that Ca2+ and Vm cues during APs are self-similar to APFI variabilities (and therefore self-similar to mean APFIs) regardless of the presence or absence or type of autonomic receptor stimulation. In other terms, we hypothesized that Ca2+ and Vm domain clock-coupling cues occurring during all APs are self-similar to each other, i.e., manifest long-range correlations in all isolated SAN cells within populations of cells that differ with respect to autonomic input, and that these Ca2+ and Vm cues during APs are also self-similar to the rate and rhythm of AP firing across the entire range of APFIs created by these cues in all isolated SAN cells.We hypothesized that transitions in ignition  and recoignition  of APs an = 230) of single rabbit SAN cells to which we applied CRs [carbachol (CCh)] to one subset of cells, βARs [isoproterenol (ISO)] to another subset, and no autonomic receptor stimulation to a third subset of cells. This created three populations of SAN cells having APFIs distributed across the entire physiologic range. We measured intracellular Ca2+ or membrane potential in these cells to (1) characterize the times to ignition onset and times to 90% recovery of Vm and Ca2+ parameters during APs in AP time series and (2) to determine the correlations of these Vm and Ca2+ kinetic parameters to each other during APs, to APFI variability . Thus, the data set to be analyzed consisted of 12 different kinetic parameters in each cell population ; six parameter means, three each in the Ca2+ and Vm domains; and six parameter variabilities (SDs) around the means. To determine the degree of self-similarity among Vm and Ca2+ domain parameters, we constructed density distribution plots and applied correlation, power law, and principal component (PC) analyses to Ca2+ and Vm domain data sets separately and to the combined Ca2+ and Vm data sets. We further extended our perspectives from cell population and single-cell levels downward to the molecular scale by performing numerical modeling simulation and analyzing variabilities of ion currents and Ca2+ with respect to APFI to determine whether these ion currents and Ca2+ also obeyed a power law across autonomic states.To test these hypotheses, we studied a large population . The experimental protocols have been approved by the Animal Care and Use Committee of the NIH (protocol #457-LCS-2024). Materials and methods briefly presented here are detailed in Single, spindle-shaped, spontaneously beating SAN cells were isolated from the hearts of New Zealand rabbits  as described previously .90, and the time to ignition onset (TTIO) measured by the time at which diastolic membrane potential dV/dt accelerates to 0.15 V/s (Time series of spontaneous APs were recorded in subsets of freshly isolated SAN cells using the perforated patch-clamp technique with Axopatch 200B patch-clamp amplifier (Axon Instruments)  at 34°C 0.15 V/s , which r0.15 V/s .Vm and Ca2+ in a separate subset of cells  with an additional randomly fluctuating current around its zero-mean value, known as perturbation current or Iper  under cell membrane was also simulated during the three autonomic states. For all items, we measured variability of their peak amplitudes and amplitudes at −40 mV during DD.Variability of a2+ cues  that cana2+ cues ] subject2+ or Itot), it affected the variability of ion currents and Ca2+ the same way, and the predicted variabilities for many parameters differed substantially from that of APFI:Model simulation results are presented in (1)If variability was substantial: in the basal state and in ISO If variability was similar to or larger than APFIV; the variability of If decreased in CCh.(2)INCX variability was also substantial: at −40 mV, it was substantially larger than that of APFIV (except in CCh when Iper was added to Itot); variability of INCX peak amplitude  was similar to that of APFI in the basal state and ISO, but became reduced in CCh.(3)IKr variability was substantially less than APFIV under all conditions.(4)ICaT variability was the largest among ion currents, being similar to that of INCX, in CCh when Iper was added to Ca2+ release.(5)ICaL variability was always less than that of APFIV; at −40 mV, it was greater in ISO than in basal state and CCh.Peak (6)2+ release flux in the basal state and ISO at −40 mV was greater than or similar to APFIV; in CCh, variability of Ca2+ release flux was less than that of APFI.Variability of CaSome components exhibited power law behavior over a wide range of APFI over all conditions tested .2+ data during this time of the cycle, i.e., at −40 mV. To this end, we applied the statistical tests utilized for experimental data to simulated data (for the scenario when Iper was added to Itot).We next determined whether self-similarity across autonomic states observed for experimental data during the ignition phase is also applied to simulated ion currents or Ca2+ amplitudes during AP ignition (−40 mV) across the three autonomic states are self-similar to each other, strongly correlated to each other, as were experimentally measured parameters  it is fully determined by only Ca2+. That is why we have 100% correlation of INCX and Ca2+. ICaT strongly correlated with Ca2+ variations, because the stronger Ca2+ signal is linked to the higher DD rate and hence stronger (time-dependent) activation of ICaT. Surprisingly, IKACh amplitude was also highly correlated with Ca variations.Simulated ion currents and Carameters . These tIf and IKr at −40 mV did not depend on variations of Ca2+, but their mean values strongly depended on Ca2+ across the autonomic states. If activation and IKr deactivation are early DD mechanisms and do not seem to interplay with Ca2+ at the ignition onset at −40 mV in a given cycle.Variations in INCX, ICaT, IKr, [Ca], ICaL, IKACh, and If, all at −40 mV). Although the ranges of absolute values of these simulated parameters substantially vary, all simulated parameters are self-similar, i.e., fit by a single line (r = 0.998) with a slope of unity, resembling Poincaré relationship of experimentally measured AP parameters  cells. Absolute values of times to AP ignition onsets and to 90% recovery intervals in Ca2+ and Vm domains during APs and APFIs differed within and among individual cells in cell populations and different autonomic states and differed markedly among cells of the three populations of cells with differential autonomic receptor stimulation. Our novel finding is that although differing markedly in absolute values, Ca2+ and Vm parameters were self-similar to each other during APs and self-similar to APFIs, not only within and among different cells within each of the three populations of cells studied, but remarkably, among all cells, regardless of the autonomic receptor stimulation profile. Thus, Ca2+ and Vm domain kinetic transitions  during APs, individual APFI, and mean APFIs within AP time series manifest long-range correlations  across the entire broad range of APFIs, regardless of whether autonomic receptors of these cells are stimulated and regardless of the type of autonomic receptor stimulation.We measured membrane potential and Cavice versa, the lower the degree of order among clock molecular activation states, the lower the aggregate synchronization among clock molecular functions, the greater the variability of APFIs, and the longer the mean AP cycle interval.The degree to which molecular activation states within each clock and between clocks are synchronized during APs determines when the next AP will occur, i.e., the APFIV and mean APFIs within a cell and across the entire population of single SAN cells studied: the higher the degree of order (self-organized activation of clock molecules), the more ordered and less variable the aggregate of kinetic functions, the least variability of APFIs, and the shorter the mean APFI; Vm and Ca2+ domain intervals during APs and APFIs across diverse populations of single SAN cells that were not physically connected to each other.Self-similar or fractal-like beating rate variability among cardiac cells in culture has been previously identified in a number of studies but only when cells were confluent or electrically connected to each other. This behavior has been attributed to influences of tonic or phasic resetting of membrane potential or to mechanical factors via cell-to-cell connections . Our novThus, self-similar distributions of order that have been demonstrated to occur in other instances throughout nature  also exi2+, cAMP signaling, and PKA and CaMKII-dependent clock protein phosphorylation are the cues that regulate the activation kinetics of molecules that control pacemaker functions in single SAN cells  some degree of disorder that stems from its key constituent proteins operating  intrinsically within their conformational flexibilities and heterogeneity. The balance of order/disorder is linked to molecule interactions  that allow them to operate cooperatively as an ensemble or system with various degrees of synchronization  that is reflected in respective variability of the output function of the system, i.e., APFIV in our case.Both voltage and Ca2+ regulatory functions during AP cycles across the entire physiologic range of AP cycles to reflect a concordance in the degrees of activation of molecules that drive these regulatory functions. Importantly, Ca2+ and Vm cues not only regulate the synchronization clock of molecular activation states but are also regulated by the degree of synchronized activation of molecules determined by these cues (recursion). Because membrane and Ca2+ clocks become coupled in the context of the electrochemical signal that waxes and wanes to cause the AP cycle, the extent of self-organized molecular activation within each clock indirectly affects self-organization of molecular activation of the other clock operating within the coupled-clock system. And because scaling of mean APFIs among all cells is self-similar to APFIV among cells, AP firing variability and mean APFI are determinants of the Ca2+ and Vm cues that determine kinetic intervals during an AP: a recursive, feed-forward process.Thus, we interpret the experimentally measured concordant behavior of surface membrane and Ca2+ and Vm cues during an AP determine not only the characteristics of that AP but also when the next AP will occur and the mean APFI within an AP time series.Changes in Ca2+ influx and indirectly reduces Ca2+/CaMKII-AC–dependent phosphorylation of Ca2+ cycling proteins, reducing the SR Ca2+ cycling kinetics and increasing the variability of LCR periods.A prolongation of the mean APFIs, itself, contributes to the concurrent increase in the APFIV at a long mean APFI: because an increase in mean APFI reduces net Ca2+ and M clock activation: as the mean AP interval shortens, less time elapses between APs, and therefore at shorter intervals, less time is required than at longer intervals for molecules to retain (remember) the synchronizing influences imparted by the preceding AP. This causes the relationship of mean APFI to APFIV of isolated SAN cells to be non-linear  are more effective than longer periods , because during very long AP cycles, Ca2+ activation states of some molecules become more unsynchronized. At very short times following a large voltage oscillation , many molecules of a given molecular species in relatively inactivated state may not optimally respond to activation cues . As the time following a prior activation increases, although a subpopulation of molecules of given species may regain full ability to respond to activation cues, substantial variability in the activation status of other molecules of that species still may exist, limiting the number of molecules that can respond to (be recruited by) an activation cue. Our results provide novel clues to the cellular basis for the observation that an AP occurrence, itself, influences the range of APFIs that immediately follow it  a direct effect, due to cAMP or phosphorylation-dependent activation of clock proteins and (2) an indirect effect by altering the APFI, which alters the cell Ca2+ activation cues that are directly modulated by autonomic receptor stimulation. Specifically, βARs and CRs, respectively, not only reduce or increase mean APFI, but also, respectively, shift variability within distributions of Ca2+ and Vm functions in the same direction : components contributing to DD  exhibit a larger cycle to cycle variability, whereas components contributing to generation of all-or-none AP characteristics exhibit less variability (peak ICaL and IKr). This result is in accord with the idea of order/disorder transitions during AP cycle . This self-acceleration ignition mechanism results in the power law behavior predicted by the model.However, our simulations also provided some unexpected, interesting results: via INCX . There iIf also followed a power function over a broad range of APFIs, albeit in a noisy manner manifesting some extremely long APFIs in CCh. The current that fluctuated most with respect to variabilities in APFI turned out to be ICaT, the peak amplitude of which also reflects DD dynamics. When DD is rapidly accelerating (as it does at shorter cycles), ICaT peak quickly activates and achieves a higher peak amplitude, and vice versa, when DD is slower at longer APFIs, ICaT becomes inactivated over time without achieving a peak. In log–log plots, this forms a straight line for almost the entire range of APFIs (power law behavior), except extremely long APFIs when variations in  slow DD dynamics have almost no effect on ICaT peak. Thus, simulations of biophysical components within the pacemaker cell system exhibited a power law behavior over a wide range of APFIs that encompasses the broad range of APFIs measured experimentally.Peak Observation of model simulations through analytic lenses applied to experimental data indicated that (as was the case for the experiment data) the simulated variables are self-similar to each other across a broad range of APFIs within the three autonomic states .ICaL model was adopted from the Kurata model .EL and VM designed the project. DY, AL, IZ, YY, TV, and BZ performed the experiments and analyzed the results. DY, CM, and ST did the statistical analyses. DY and VM performed the numerical simulation. DY and EL wrote the manuscript with the support from YY and VM. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.