Functional characteristics of Heracleum sosnowskyi Manden. terminal buds during preparation for overwintering

Based on the study of the physiological and biochemical characteristics of Heracleum sosnowskyi buds we iden-tified functional adaptations during the preparation of plants for overwintering. The freezing point of water in the buds tissues was -12 & ocy;C in October, while maintaining high water content (more than 80%). Buds has a relatively high efficiency of respiration at low positive temperatures (2-5 & ocy;C), which favors morphogenesis processes in the shoot vegetative cone in autumn. During the preparation for overwintering the buds accumulated osmoregulators - soluble sugars, free amino acids, including proline. A relatively high level of cytokinin growth hormones was found in the buds tissues. This contributes to morphogenesis processes and increases plant cold tolerance. We found that in December the abscisic acid (a growth inhibitor and resting hormone) content increases and the level of cytokinins decrease. Heracleum sosnowskyi formed buds differing in the photosynthetic pigments content. Buds with green scale leaves accumulated the greatest amount of chlorophylls and carotenoids, while those with red-brown and yellow ones accumulated the least. The carotenoids accumulation in the green buds tissues protects the formed photosynthetic apparatus at low positive temperatures in autumn. The results on the functional state of H. sosnowskyi terminal buds in natural populations indicate the absence of deep dormancy in plants, and morphogenesis processes in meristems tissues are limited by winter temperatures.