Osmotic stress is a major factor reducing the growth and yield of many horticultural crops worldwide. To reveal reliable markers of tolerant genotypes, we need a comprehensive understanding of the responsive mechanisms in crops. In vitro stress induction can be an efficient tool to study the mechanisms of responses in plants to help gain a better understanding of the physiological and genetic responses of plant tissues against each stress factor. In the present study, the osmotic stress was induced by addition of mannitol into the culture media to reveal biochemical and genetic responses of tea microplants. The contents of proline, threonine, epigallocatechin, and epigallocatechin gallate were increased in leaves during mannitol treatment. The expression level of several genes, namely DHN2, LOX1, LOX6, BAM, SUS1, TPS11, RS1, RS2, and SnRK1.3, was elevated by 2–10 times under mannitol-induced osmotic stress, while the expression of many other stress-related genes was not changed significantly. Surprisingly, down-regulation of the following genes, viz. bHLH12, bHLH7, bHLH21, bHLH43, CBF1, WRKY2, SWEET1, SWEET2, SWEET3, INV5, and LOX7, was observed. During this study, two major groups of highly correlated genes were observed. The first group included seven genes, namely CBF1, DHN3, HXK2,SnRK1.1, SPS, SWEET3, and SWEET1. The second group comprised eight genes, viz. DHN2, SnRK1.3, HXK3, RS1, RS2,LOX6, SUS4, and BAM5. A high level of correlation indicates the high strength connection of the genes which can be co-expressed or can be linked to the joint regulons. The present study demonstrates that tea plants develop several adaptations to cope under osmotic stress in vitro; however, some important stress-related genes were silent or downregulated in microplants.

Currently, the preservation of the biodiversity of cultivated plants and species of natural flora is an urgent task for scientific institutions. At the same time, biotechnological methods in the preservation of the plant gene pool are of particular importance. The article presents the results of research on the maintenance and study of the in vitro collection of subtropical fruit, berry, and flower-and-ornamental crops, as well as species of natural flora included in the Red Books of the Russian Federation and the Krasnodar Territory. The work on creating an in vitro plant collection began at the Subtropical Scientific Center of the Russian Academy of Sciences in 2010. Currently, the collection includes more than 113 plant species, which belong to 39 species and 83 varieties from 22 families. The most representative collections are from the following families: Amaryllidaceae J.St.-Hil., Asteraceae Giseke, Orchidaceae Juss., and Rosaceae Juss. The majority of the in vitro collection (73 %) consists of flower crops, while 14.7 % consists of endangered and rare species of natural flora, and the remaining 12.3 % consists of subtropical fruit and berry crops culture. The purpose of our research is to study and preserve the plant collection in vitro. The factors influencing the timing of subcultivation and the duration of deposit have been identified. It has been established that the content of osmotic substances (mannitol, sorbitol) and ABA in the nutrient medium, as well as low air temperature (+7…+15 ℃) and low illumination (500-1000 lux) affect the duration of plant cultivation. The genetic stability of plant material stored in the in vitro collection was assessed, and it was found that the ISSR and IRAP primers used in the study provided stable and reliable data that confirmed the similarity between cultivars and plants from their natural habitats. Keywords: plant collection, in vitro conditions, subtropical crops, species, osmotic substances, deposition Acknowledgements: The research was part of State Assignment FRC SSC RAS FGRW-024-0008. № 1023110900223-6-4.1.1 and FGRW-2024-0003, № 124022000093-1.