Effect of red and blue light on acclimation of Chlamydomonas reinhardtii to CO2-limiting conditions

Abstract

Effects of red (RL) and blue (BL) light on acclimation of the unicellular green alga Chlamydomonas reinhardtii to the low level of ambient CO2 were studied. C. reinhardtii cells grown at 5% CO2 and under white light (170 μmol/(m2s)) had a relatively low activity of extracellular carbonic anhydrase (CA), a low affinity for dissolved inorganic carbon, and a low rate of photosynthesis under CO2-limiting conditions. These cells readily started acclimation to the low CO2 concentration when they were exposed to atmospheric air (∼ 0.03% CO2) under RL or BL (150 μmol/(m2 s) each). The acclimation was manifested in a significant increase in the CO2-limited rate of photosynthesis, the affinity for dissolved inorganic carbon, and the extracellular CA activity with no difference between RL-and BL-cells. Independently of light quality, the acclimation was completed for 5–7 h after cell exposure to air. As is evident from RL-and BL-dependent changes in the sum of chlorophylls and chlorophyll a/b ratio, transfer of C. reinhardtii cells to air and RL or BL triggered also the process of algal photosynthetic adaptation to light quality. However, this process did not interfere with acclimation to low CO2 because started 4 h later. On the basis of similarity in the low CO2-induced changes under RL and BL, it is concluded that acclimation of C. reinhardtii to CO2-limiting conditions does not depend on light quality.