PHOTOSYNTHESIS AND LOW CO2 INDUCIBLE PROTEIN-SYNTHESIS IN A NEWLY ISOLATED HIGH CO2-PREFERRING MUTANT OF CHLAMYDOMONAS-REINHARDTII

The effect of external CO2 concentrations on the protein synthesis in Chlamydomonas reinhardtii wild-type is compared with that of a new hig h 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-t ype induces three new ones (21, 36 37 kDa), but pyr-45 induces no new polypeptides. Total proteins from pyr-45 mutant cells do not crossreac t with antibodies against the three low CO2-inducible polypeptides of wild type. The CO2 requirement for half maximal rates of photosynthesi s decreases when pyr-45 cells are switched from high to low CO2, but n ot to the extent of wild-type cells. When exogenous carbonic anhydrase (CA) is added to these partially adapted cells, the CO2 requirement i s 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 c oncentrations in the environment and in the function of the CO2 concen trating mechanism (CCM) in Chlamydomonas reinhardtii.