Contribution of primary and stored photosynthates to photorespiration and respiration in the light and in the dark

摘要

Substrates of respiration and photorespiration are compounds formed in the reactions of the photosynthetic carbon metabolism. These compounds may by divided into two groups, primary photosynthates and stored photosynthates. Primary photosynthates are products of current photosynthesis with a turnover half-time in the order of minutes. They include the metabolites of the reductive pentose phosphate cycle, of the glycolate cycle, intermediates of starch and sucrose synthesis and glycolysis. During the exposure of leaves to ~(14)CO_2 these compounds are saturated with ~(14)C within 10 min (Ivanova et al., 1993). Stored photosynthates are the end products of photosynthesis accumulating during the day in photosynthesizing leaves. These metabolites arecharacterized with turnover halftime in the order of hours and include the compounds such as starch, sucrose and vacuolar acids. Long-term exposure (2 to 3 h) of leaves to ~(14)CO_2 is required to achieve any measurable level of the specific radioactivity of carbon in these compounds. It has been shown that primary and stored photosynthates are used as substrates of both respiration and photorespiration (Parnik and Keerberg, 1995). In this paper we present data on the rates and ratio of consumption of primary and stored photosynthates in decarboxylation reactions in the light and in the dark. Six C_3-species with different ability of starch synthesis has been studied.