Changes of Ribulose Bisphosphate Carboxylase/Oxygenase Content Ribulose Bisphosphate Concentration and Photosynthetic Activity during Adaptation of High-CO2 Grown Cells to Low-CO2 Conditions in Chlorella pyrenoidosa

摘要

Changes of some photosynthetic properties of high-CO2 grown cells of Chlorella pyrenoidosa during adaptation to low-CO2 conditions have been investigated. The Km value of photosynthesis of the high-CO2 grown cells for dissolved inorganic carbon was 3.3 millimolar and decreased to 25 to 30 micromolar within 4 hours after transferring to air. In the presence of saturating CO2 concentrations the photosynthetic activity of the high-CO2 grown cells was 1.5 times as high as that of the low-CO2 grown cells. There was a significant rise of the photosynthetic activity during adaptation of the high-CO2 grown cells to air, followed by a steady decrease. The activity of ribulose 1,5-bisphosphate carboxylase/oxygenase in both the high- and low-CO2 grown cells was close to the photosynthetic activity of the cells. The concentration of ribulose 1,5-bisphosphate (RuBP) was higher in the low-CO2 adapting and low-CO2 grown cells than in the high-CO2 grown cells regardless of the photosynthetic rate. This seems to be due to an increased RuBP regeneration activity during adaptation followed by maintenance of the new higher concentration. The RuBP level always exceeded the concentration of ribulose 1,5-bisphosphate carboxylase/oxygenase RuBP binding sites in both the high- and low-CO2 grown cells at any dissolved inorganic carbon concentration.