Changes of Ribulose Bisphosphate Carboxylase/Oxygenase Content, Ribulose Bisphosphate Concentration, and Photosynthetic Activity during Adaptation of High-CO(2) Grown Cells to Low-CO(2) Conditions in Chlorella pyrenoidosa

Abstract

Changes of some photosynthetic properties of high-CO(2) grown cells of Chlorella pyrenoidosa during adaptation to low-CO(2) conditions have been investigated. The K(m) value of photosynthesis of the high-CO(2) 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 CO(2) concentrations the photosynthetic activity of the high-CO(2) grown cells was 1.5 times as high as that of the low-CO(2) grown cells. There was a significant rise of the photosynthetic activity during adaptation of the high-CO(2) grown cells to air, followed by a steady decrease. The activity of ribulose 1,5-bisphosphate carboxylase/oxygenase in both the high- and low-CO(2) grown cells was close to the photosynthetic activity of the cells. The concentration of ribulose 1,5-bisphosphate (RuBP) was higher in the low-CO(2) adapting and low-CO(2) grown cells than in the high-CO(2) 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-CO(2) grown cells at any dissolved inorganic carbon concentration.