Photosynthesis and low CO2 inducible protein synthesis in a newly isolated high CO2-preferring mutant of Chlamydomonas reinhardtii

Abstract

The effect of external CO2 concentrations on the protein synthesis in Chlamydomonas reinhardtii wild-type is compared with that of a new high CO2-preferring mutant, designated as pyr-45. Radiolabeled wild-type and pyr-45 cells exhibit up-regulation of two polypeptides (42-45 kDa) when adapted from high (5% CO2 in air) to low CO2 (0.03%), and wild-type induces three new ones (21, 36 37 kDa), but pyr-45 induces no new polypeptides. Total proteins from pyr-45 mutant cells do not crossreact with antibodies against the three low CO2-inducible polypeptides of wild type. The CO2 requirement for half maximal rates of photosynthesis decreases when pyr-45 cells are switched from high to low CO2, but not to the extent of wild-type cells. When exogenous carbonic anhydrase (CA) is added to these partially adapted cells, the CO2 requirement is further reduced, but still not completely. The up-regulation of the 42-45 kDa polypeptides under low CO2 growth conditions suggests these changes play a role in the adaptation of algal cells to limiting CO2 concentrations in the environment and in the function of the CO2 concentrating mechanism (CCM) in Chlamydomonas reinhardtii.