ANNUAL CYCLE OF RESPIRATION IN THE LEAVES OF EVERGREEN PLANTS

Evergreen herbaceous plants Bergenia crassifolia (L.) Fritsch and Hede ra colhica (Koch.) were used to study seasonal changes in the respirat ion of leaves of various ages. In young and old leaves, seasonal chang es in respiration were similar, although respiration was controlled by different factors. Respiration of young leaves was determined by thei r growth. In overwintered leaves, enhancement of respiration in spring was caused by the activation of cell metabolism, as well as by the lo ading and export of assimilates from leaves. The alternative oxidase m ediated the respiration of young and old leaves during the spring seas on, and was involved in the respiration of old leaves during the autum n-winter season. The physiological roles of the alternative oxidase we re different in the spring and autumn-winter periods. A high level of carbohydrates in leaves and the lack of correlation between respiratio n and carbohydrate level suggest that compartmentation of carbohydrate pools might be a mechanism of respiration control. During winter, lea ves of evergreen plants were demonstrated to spend on respiration only 13% of their carbon with respect to total expenditures throughout the year. The physiological role of overwintering leaves in evergreen her baceous plants is not restricted to photosynthetic activity in early s pring (before the expansion of young leaves); these leaves seem to kee p a reserve of assimilates required for the growth of the next generat ion of leaves.