Simultaneously with CO2 fixation in plant leaves during photosynthesis, respiration processes release part of the fixed CO2 in decarboxylation reactions. In this work the significance of internal and environmental factors in regulatory mechanisms determining integration of photosynthetic and respiratory processes was studied. It was found thet all primary and stored photosynthates serve as decarboxylation substrates, however, differences in utilization of soluble end products (mainly sucrose) and starch were observed. In photosynthesizing leaves starch is not decomposed ¿ it is used only under conditions not enabling photosynthesis (in the dark, at high temperature, in CO2-free atmosphere). In these circumstances, the amount of substrate for respiration determines, at least partly, the rate of respiratory decarboxylation; in other cases, the redox state inside the cell is more significant.

Hiie Ivanova (PhD) graduated from Tartu University as biologist. She was a researcher at the Institute of Experimental Biology of the Estonian Academy of Sciences and at the Estonian University of Life Sciences. Main field of reasearch has been regulation of photosynthetic, photorespiratory and respiratory metabolism in plants.