Cryopreservation of rare plant materials is an important approach for preserving germplasms and is a good added concept to tissue banking. The preservation of embryogenic cell suspensions is even more valuable as the tissues facilitate in producing millions of embryos, plantlets and generates transgenics en masse. Catharanthus roseus is a medicinally important plant that produces a variety of anticancerous phytocompounds and needs conservation of alkaloid producing cell lines. In this study, embryogenic tissue banking has been attempted in C. roseus by the two-step cryopreservation method combining cryoprotection and dehydration. Prior to plunging into liquid nitrogen (LN), the tissues were exposed to osmotic-and cryoprotective agents. Two osmotic agents (sugar and sorbitol) and three cryoprotective compounds, polyethylene glycol (PEG), dimethyl sulfoxide (DMSO) and glycerol were used at varying concentrations to protect cells from freezing damages. Both sucrose and sorbitol increased callus biomass post-cryopreservation; the influence of sucrose was however, more prominent. Embryogenic tissue treated in medium with 0.4 M sucrose for 2 days followed by 5% PEG for 2 h showed maximum viability before (83%) and after (55%) cryopreservation, high regrowth percentage (77%) and produced an average 9 cell colonies per Petri dish. Additionally, dehydration (1-5 h) was tested to reduce water content for improving viability and regrowth of cryopreserved embryogenic cells. Among the various tested cryoprotective conditions, the highest (72%) viability was observed following the combination of treatments with 0.4 M sucrose (2 days),10% PEG (2 h) and dehydration (2 h). Maximum regrowth percentage (88%) and 12 colonies/petri dish was noted in combination of 0.4 M sucrose + 5% PEG. The cryopreserved calli differentiated into somatic embryos (52.78-54.33 globular embryos/callus mass) in NAA (0.5 mg/l) and BAP (0.5-1.0 mg/l) added media. Plantlets were successfully regenerated from cryopreserved tissue and the 2C DNA was estimated through flow cytometry. The genome size of cryopreserved regenerant was 1.51 pg/2C, which is similar to field-grown Catharanthus plants. Vinblastine and vincristine levels were nearly the same in mother plant's and frozen (cryopreserved) leaf tissue. The post cryopreservation embryogenesis protocol may be used for continuous production of plants for future applications.
© 2022. The Author(s).