Abstract
Rates and products of photosynthetic 14CO2 fixation by division synchronized cultures of Euglena gracilis strain Z were determined over the cycle. Rate of 14CO2 fixation doubled in a continuous manner throughout the light phase followed by a slight reduction of photosynthetic capacity in the dark phase. Greater 14C incorporation into the nucleic acid-polysaccharide fraction occurred with mature cells. Products of 14CO2 fixation varied markedly over the cycle: although with mature cells 14C-labeled sucrose was not detected, with dividing cells this was the main sugar labeled; in young cells 14C maltose was formed. Cells removed at end of dark phase accumulated 14C in glycolate, whereas at other stages over the cycle less 14C was present in glycolate, and this was accompanied by a rapid incorporation of 14C into glycine and serine. Glycerate was an early and major product of photosynthesis with cells at the mature stage of the cycle.
Changes in ribulose 1,5-diphosphate carboxylase activity paralleled changes in photosynthetic rate, but activity was not great enough to account for the observed rates of CO2 fixation at most stages of the division cycle investigated.
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