ZINC-MICROELEMENT OF REFERENCE IN APPLE NUTRITION
This paper aims to present the risk of being exposed apple trees to zinc deficiency, within an bifactorial experience with fertilizers. Mobile Zn content in soil, on one hand and total zinc content in plant material (leaves) on the other hand, as mobile phosphates content in soil, represents agrochemical indices for assessing the probability of zinc deficiency. These indices determined during two years of experimentation, can be quantified in two synthetic indicators IRPM mobile phosphates reaction index in soil, used for chernozems, that express and explain the influence of pH and available phosphorus content (P-AL ppm) on Zn mobility in soil and its availability to plants; and ICZn zinc deficiency index, which takes into consideration the value of mobile Zn content in soil, being more significant in order to predict the probability of zinc deficiency appearance. Folowing the fertilization of experimental variants, we analyzed the data obtained during two consecutive years of experience, and noticed that available phosphorus content in soil increased gradually, while mobile Zn, although increasing quantity, it lies within suboptimal limits. Together these values and soil pH, which has the tendency to rise up to 8.00, the two indices calculated ICZn and IRPM, clearly indicates that the probability of deficiency in zinc appearance is medium to large, ICZn take values between 1.39 and 3.13, while IRPM take values between 0.117 and 0.232.
Zinc deficiency up-regulates expression of high-affinity phosphate transporter genes in both phosphate-sufficient and -deficient barley roots.
Phosphate (P) is taken up by plants through high-affinity P transporter proteins embedded in the plasma membrane of certain cell types in plant roots. Expression of the genes that encode these transporters responds to the P status of the plants, and their transcription is normally tightly controlled. However, this tight control of P uptake is lost under Zn deficiency, leading to very high accumulation of P in plants. We examined the effect of plant Zn status on the expression of the genes encoding the HVPT1 and HVPT2 high-affinity P transporters in barley (Hordeum vulgare L. cv Weeah) roots. The results show that the expression of these genes is intimately linked to the Zn status of the plants. Zn deficiency induced the expression of genes encoding these P transporters in plants grown in either P-sufficient or -deficient conditions. Moreover, the role of Zn in the regulation of these genes is specific in that it cannot be replaced by manganese (a divalent cation similar to Zn). It appears that Zn plays a specific role in the signal transduction pathway responsible for the regulation of genes encoding high-affinity P transporters in plant roots. The significance of Zn involvement in the regulation of genes involved in P uptake is discussed.
New Sweet-Tasting C21-Pregnane Glycosides from Pericarps of Myriopteron extensum.
Ten novel C21 pregnane glycosides, extensumside C-L (1-10), were isolated as highly sweet-tasting substances from the edible pericarps of Myriopteron extensum (Wight) K. Schum by sensory-guided fractionation and purification. Their structures were determined through 1D and 2D NMR, such as HSQC, HMBC, 1H-1H COSY, HSQC-TOCSY, and ROESY, as well as other spectroscopic analysis combined with chemical evidence. These compounds shared the same aglycone, 3β,16α-dihydroxy-pregn-5-en-20-one, and contained the deoxysugar chain and the glucose chain which were linked to C-3 and C-16 of the aglycone, respectively. The sweetness potency was evaluated by a human sensory panel test and preliminary structure-taste relationship was discussed. The sweetness intensities of these compounds are between 50 and 400 times greater than that of sucrose. Furthermore, quantitation analyses of compounds 1, 3, 4, and 6 in different parts of M. extensum indicated that the concentrations of these sweet components in the pericarps are obviously higher than those in stems and roots.