the present invention provides a simple , fast and cheap method for cryopreserving ( plant , including algae ) cells , genetically modified ( plant ) cells , organelles or tissue cultures . the technique is based on the protecting properties of silica matrices at low temperature (− 30 ° c . or lower down to − 196 ° c ., preferably − 70 ° c . or lower down to − 196 ° c .) that can be used as an original , simple and efficient technique for the cryopreservation of ( plant , including algae ) cells , genetically modified ( plant ) cells , organelles or tissue lines in common laboratory freezers . silicon is naturally present in soil in the form of silicates ( sio 2 · nh 2 o ). these mineral phases are weathered in water to produce monomeric orthosilicic acid ( si ( oh ) 4 ) and some disilicic acid which are taken up , transported and deposited as amorphous silica throughout the plant , particularly in the cell walls but not the vacuoles of the plant . several reports highlighted that these si species can improve plant resistance to bacterial and fungal attacks . additionally , silica species alleviate a wide range of abiotic stresses , including nutrient imbalances , salinity , heavy metal toxicity , water stress , uv radiation , heat and freezing stress . the claimed process of the invention requires neither specific apparatuses to control the cooling and / or warming rates , nor costly liquid nitrogen . the host structures maintain plant cells viability and do not impede their proliferation after a freeze - thaw cycle . the main advantage of encapsulating ( plant ) cells within a silica matrix is that entrapped cells are more resistant to biotic ( e . g . bacteria ) or abiotic stresses ( e . g . heat , water stress and heavy metals ). because silica gel is a non - toxic compound compared to typical cryo - additives , cells can be successfully cryopreserved for short or long periods of time ( longer than 2 years ). based on this technique , the development of commercial plant - derived pharmaceuticals could become a more convenient approach according to recognized and well established guidelines . therefore , the present method is based upon the unexpected protecting effect of silica matrices at low temperature ( at about − 30 ° c . or lower , down to − 196 ° c ., preferably at about − 70 ° c ., down to − 196 ° c .) which can be used as an original , simple and efficient technique for long - term cryopreservation of ( plant , including algae ) cells , genetically modified ( plant ) cells , ( plant , including algae ) cell lines , organelles ( such as e . g ., thylakoids ) or tissues , in standard laboratory freezers , as well as in centers ( such as the atcc ) dedicated for the conservation , especially cryopreservation , of cells and other biological materials . a ( plant ) cell culture ( such as , e . g ., arabidopsis thaliana ) can be successfully cryopreserved by the method according to the invention , which comprises three essential steps . the method of the invention comprises three essential and consecutive steps : the first step comprises the encapsulation of ( plant , including algae ) cells , genetically modified ( plant ) cells , ( plant , including algae ) organelles ( such as thylakoids ) or ( plant , including algae ) tissues within a porous silica matrix via a sol - gel process . the obtained matrix , silica - based sol made of one or more silica precursor and one or more cryoprotectant ( s ). the silica precursor ( s ) is ( are ) chosen from the group consisting of a polysilicic acid ( h 2 sio 3 ) n ( preferably metasilicic acid h 2 sio 3 ), a silica hydroxide , a silica alkoxide ( such as tetramethyl orthosilicate ( tmos ), tetraethyl orthosilicate ( teos ), tetrapropyl orthosilicate ( tpos ), tetrakis ( 2 - hydroxyethyl ) orthosilicate ( egms ), tetrakis ( 2 - hydroxypropyl ) orthosilicate ( pgms ) and tetrakis ( 2 , 3 - dihydroxypropyl ) orthosilicate ( glms )), a silicate ( such as sodium or potassium silicate ), silica nanoparticules , sorbitylsilane , ormosils ( organic modified silicas ), trimethoxymethylsilane , dimethoxydimethylsilane , tmos ( tetramethoxysilane ), dgs ( diglycerylsilane ), or a mixture thereof . more preferably , the silica precursor is the polysilicic acid ( h 2 sio 3 ) n , trimethoxymethylsilane , dimethoxydimethylsilane or a mixture thereof . moreover , further additives , such as silica colloids ( e . g ., ludox ®), silica co - precursors , or nanoparticles of silica can be added to the silica precursor solution . the cryoprotectant ( s ) is ( are ) preferably selected from the group consisting of dmso ( dimethyl sulfoxide ), an amino acid ( such as proline or glycine ), a zwitterionic compound ( betaine ) and a saccharide ( trehalose , sucrose ), a glycol ( such as ( poly ) ethylene glycol or ethylene glycol ) or a polyol ( or polyalcohol , such as sorbitol , maltitol , glycerol , erythritol , xylitol , arabitol ( lyxitol ), mannitol , lactitol , isomaltitol , etc ) or a mixture thereof . the concentration of the silica precursors used can vary between about 5 % and about 10 % ( wn ). the type of silica precursors may influence the efficiency of the cryopreservation process . preferably , the cryoprotectant ( s ) is ( are ) mixed with the silica precursor at a concentration between about 1 % and about 10 % ( dmso ) and between about 0 . 2 m and about 1 . 0 m ( sucrose ), respectively . the second step ( subsequent step ) involves an incubation period of the obtained mixture at room temperature , preferably in a controlled room ( at a temperature comprised between about 4 ° c . and about 20 ° c .) for a period of more than 1 hour , preferably from about 6 hours to about 48 hours or longer . the prepared hybrid gels are preferably kept in a closed flask . the last step includes the transfer of the resulting hybrid silica gels in a laboratory freezer ( at about − 30 ° c . or lower , down to − 196 ° c ., preferably at about − 70 ° c . down to − 196 ° c .) without any specific precautionary measures . the recovery of the ( plant ) cell suspension can be obtained by a quick warming of the sample vials at room temperature for a short time , for about 5 minutes to about 10 minutes . thawed silica gels are then spread on a plate containing a solid nutrient medium . the host structures maintain ( plant ) cells viability and do not impede with their proliferation after a freeze - thaw cycle . after a period of about 7 days to about 14 days , recovered hybrid silica - cell materials are transferred into a flask containing fresh liquid medium . alternatively , the cultivars are maintained on a solid nutrient medium . this method is effective , rapid and cheap and therefore , more efficient than current methods used , such as slow freezing techniques or dehydration of immobilized cells . another aspect of the present invention is related to a cryopreservation kit especially a cryopreservation kit for ( plant , including algae ) cells , genetically modified ( plant ) cells , ( plant , including algae ) organelles ( such as thylakoids ) or ( plant , including algae ) tissues that could be used in the method according to the invention and which comprises a silica matrix made of one or more silica precursor , such as polysilicic acid , and one or more cryoprotectant ( s ). the kit according to the invention can comprise these elements for the matrix according to the invention in separate vials . the silica precursor ( s ) is ( are ) preferably selected from the group consisting of a polysilicic acid ( h 2 sio 3 ) n ( preferably metasilicic acid h 2 sio 3 ), a silica hydroxide , a silica alkoxide ( such as tetramethyl orthosilicate ( tmos ), tetraethyl orthosilicate ( teos ), tetrapropyl orthosilicate ( tpos ), tetrakis ( 2 - hydroxyethyl ) orthosilicate ( egms ), tetrakis ( 2 - hydroxypropyl ) orthosilicate ( pgms ) and tetrakis ( 2 , 3 - dihydroxypropyl ) orthosilicate ( glms )), a silicate ( such as sodium or potassium silicate ), silica nanoparticules , sorbitylsilane , ormosils ( organic modified silicas ), trimethoxymethylsilane , dimethoxydimethylsilane , tmos ( tetramethoxysilane ), dgs ( diglycerylsilane ), or a mixture thereof . the cryoprotectant ( s ) is ( are ) the one described above , such as dmso ( dimethyl sulfoxide ), saccharides ( trehalose , sucrose ), amino acids ( proline or glycine ) zwitterionic compounds ( betaine ), glycols , polyols ( or polyalcohols , such as sorbitol , maltitol , glycerol , erythritol , xylitol , arabitol ( lyxitol ), mannitol , etc .) or a mixture thereof . preferably , the concentration of the silica precursors in the matrix can vary between about 5 % and about 10 % ( wn ). in a preferred embodiment , the cryoprotectant ( s )( dmso and sucrose ) is ( are ) mixed with the silica precursor at a concentration between about 1 % and about 10 % ( dmso ) and between about 0 . 2 m and about 1 . 0 m ( sucrose ), respectively . the present invention will be described in the following examples in reference to the enclosed figures as non - limiting preferred embodiments of the invention . fig1 represents the determination of optimal conditions for the cryopreservation of a . thaliana cells via the monitoring of o 2 - uptake ( dark respiration ) at 20 ° c . the metabolic activity of plant cells was evaluated after each of the three steps of the cryopreservation process . effects of the incubation time of hybrid gels at different temperatures on cell activity after cryopreservation ( a ). effects of sucrose ( b ) and dmso ( c ) concentrations on cell preservation . 100 % corresponds to the oxygen consumption of cells not having undergone any freeze - thaw cycle . the mean values ( n = 3 ) are presented with the standard deviations . fig2 represents the role of silica species in the cryopreservation of a . thaliana cells . comparison of oxygen consumption of recovered cells that were pre - incubated with either polysilicic acid ( a ) or silica nanoparticles ( b ). the mean values ( n = 3 ) are presented with the standard deviations . fig3 represents the long - term preservation of plant cells . effect of storage time of hybrid gels at − 80 ° c . on post - thaw metabolic activity . the mean values ( n = 3 ) are presented with the standard deviations . silica nanoparticles ( 5 - 15 nm ), dipotassium tris ( 1 , 2 - benzenediolato - o , o ′) silicate , murashige and skoog medium ( msmo ), sucrose , dimethyl sulfoxide ( dmso ), potassium hydroxide , oxalic acid dehydrate 99 %, ammonium molybdate tetrahydrate 99 %, 4 ( methylamino ) phenol sulfate 99 %, sodium sulfite 99 %, hydrochloric acid 37 %, sulfuric acid 95 %, kinetin and 1 - naphtalenacetic acid were purchased from sigma - aldrich . poly ( silicic acid ) s ( h 2 sio 3 ) was prepared from sodium silicate solution ( assay 25 . 5 - 28 . 5 %, merck ) as described by c . f . meunier , j . et al . ( j . mater . chem ., 2010 , 20 , 929 - 936 ). amplex red hydrogen peroxide assay kit and membrane filters of a pore size of 0 . 2 μm were obtained from molecular probes co and sartorius , respectively . photomixotrophic suspension - cultured cells derived from the leaves of arabidopsis thaliana strain l - mm1 ecotype landberg erecta were cultivated in msmo medium ( 4 . 4 g l − 1 , ph 5 . 7 ) supplemented with 3 % sucrose , 0 . 05 mg l − 1 of kinetin and 0 . 5 mg l − 1 of 1 - naphthaleneacetic acid . cells were maintained under 16 / 8 h light / dark photoperiod , at 22 ° c ., on a rotary shaker at 115 round . per . minutes ( r . p . m .) 10 ml of cell suspensions ( 3 days after the latest subculture ) were concentrated ten times in order to obtain a cell density of about 120 mg of fresh weight per milliliter . the plant cells were then transferred and mixed with 4 ml of a cryoprotecting silica sol ( between 1 m and 3 m h 2 sio 3 , between 1 % and 10 % ( v / v ) dmso , between 0 . 2 m and 1 m sucrose , about 4 . 4 g l 1 msmo powder , ph value adjusted to between 4 and 8 with 0 . 2 m koh ) which was filter - sterilized with 0 . 20 μm membrane filters and refrigerated at 4 ° c . the mixture was then incubated in a cold room ( 4 ° c .) during about 1 to 6 hours . in the meantime , gelation occurred . the resulting hybrid silica gel was finally transferred and stored in a laboratory freezer ( at about − 80 ° c .). hybrid silica matrices were quickly thawed by warming the sample vial at room temperature for about 5 - 10 minutes . thawed gels were then spread on a plate containing a solid medium ( 0 . 8 % agar , 4 . 4 g l − 1 msmo medium supplemented with 3 % sucrose , 0 . 05 mg l − 1 of kinetin and 0 . 5 mg l − 1 of 1 - naphthaleneacetic acid ) and incubated for about 7 days at 22 ° c . under 16 / 8 h light / dark photoperiod . after this period , recovered hybrid silica - cell materials were transferred into an erlenmeyer flask containing 20 ml of fresh liquid medium . the physiological functions of cells was determined from about 1 hour to about 7 days after thawing by monitoring o 2 - uptake at 20 ° c . with a clark - type oxygen - electrode ( oxy - lab manufactured by hansatech instruments , uk ). cell viability was confirmed with a vital dye staining ( fluorescein diacetate , fda ). thawed cells were incubated with 5 mm fda at room temperature for 5 minutes . micrographs were collected at 536 / 40 nm with a color camera ( dsri1 , nikon ) by illuminating the samples with a 482 / 35 nm excitation light using a fluorescent microscope ( multizoom az100 microscope purchased from nikon ). the ability of recovered cells to grow and form so - called callus tissues was also used as an indicator of cell viability . the metabolic activity ( monitoring o 2 - uptake ) of plant cells evaluated in after each of the three steps of the cryopreservation process : encapsulation ( immobilization ), incubation ( 4 ° c .) and freezing (− 80 ° c .). in figure a , the effect of the incubation step of hybrid gels at different temperatures ( 4 ° c . or 20 ° c .) was evaluated on cell activity after cryopreservation . then , the effects of sucrose ( b ) and dmso ( c ) concentrations on cell preservation were evaluated . 100 % corresponds to the oxygen consumption of cells not having undergone any freeze - thaw cycles . fig1 a provides data on the optimum incubation time of the second step of process of the invention . as reported in fig1 a , the optimum incubation time varies from about 6 hours to about 48 hours . fig1 b provides data on the optimum concentration in sucrose in the cryoprotecting silica solution of the first step of the process of the invention . as reported in fig1 b , the optimum concentration in sucrose varies from about 0 . 2 m to about 1 m . fig1 c provides data on the optimum concentration in dmso in the cryoprotecting silica solution of the first step of the process of the invention . as reported in fig1 c , the optimum concentration in dmso varies from about 1 % to 10 %. role of silica species for the cryopreservation of a . thaliana cells . the experiment was performed as presented in example 1 . plant cells were transferred and mixed with 4 ml of a cryoprotecting silica sol containing different concentrations of polysilic acid ( about 0 . 4 % to about 10 %), silica nanoparticles ( about 1 % to about 12 %). fig2 compares the oxygen consumption of recovered cells that were pre - incubated with either polysilicic acid ( a ) or silica nanoparticles ( b ). as it can be derived from fig2 , polysilicic acid used as silica precursor provides a higher metabolic activity than silica nanoparticles within the concentration range tested . as reported in fig2 a , the optimum concentration in polysilicic acid varies from about 5 % to about 10 %. the experiment was performed as presented in example 1 . fig3 represents the oxygen consumption of recovered cells after storage at − 80 ° c . for time varying from one month to 24 months . plant cells cryopreserved for two years within a silica matrix are still viable as reported in fig3 .
a method is for the cryopreservation of a cell , organelle or tissue , where the cell , organelle or tissue is encapsulated in a matrix formed of an abiotic material in presence of one or more additives with cryoprotectant effect . the method provides a faster , more effective and cheaper way to cryopreserve biological material .