OSMOTIC STRESS CAUSED BY MANNITOL AND ITS EFFECT ON PHYSIOLOGICAL AND BIOCHEMICAL PARAMETERS OF TEA (CAMELLIA SINENSIS (L.) KUNTZE) MICRO-SHOOTS IN VITRO

Drought-induced osmotic stress is a major limiting factor in tea cultivation. With a moisture deficit, the growth of unproductive shoots is observing, with the apical meristem stopped in growth. The tea plant enters the dormant stage, during which mass formation of generative organs is observing, which leads to a decrease in yield and quality of raw materials. This period lasts from 20, in some cases up to 30 days. Breeders are facing with the task of comprehensively studying the mechanisms of response of tea plants to moisture deficiency and identifying reliable markers for assessing drought-tolerant genotypes. In this regard, targeted induction of osmotic stress in vitro is an effective tool for studying these processes and will help to reveal the physiological and biochemical reactions of plant tissues to a stress factor. In our studies, microshoots of tea of the best-zoned variety ‘Kolhida’ served as plant material, which vegetatively propagated in culture in vitro for 2 years. To study the changes caused in them by stress at the biochemical and physiological levels, a selective medium was used, where mannitol was used as an osmotic agent at a concentration of 200–300 mM. It was found that the content of 200 mM mannitol in the nutrient medium contributed to the accumulation of proline, threonine, epigallocatechin and epigallocatechin gallate in the leaf apparatus of tea microshoots. At the same time, the indicated concentration of mannitol led to a deficiency in the moisture content in the leaves and a significant change in the permeability of cell membranes, and also caused an increase in the relative electrical conductivity of tissues. Decreases in caffeine, chlorophylls, and alphaalanine were observed in the leaves. It has been established that the increased content of threonine, proline, epigallocatechin and epigallocatechin gallate in tea leaves in response to the presence of mannitol in the nutrient medium can serve as markers for the isolation of drought-resistant tea genotypes.