Reduced Inorganic Carbon Transport in a CO2-Requiring Mutant of Chlamydomonas reinhardii

Publisher Website
Google Scholar
Abstract
A mendelian mutant of the unicellular green alga Chlamydomonas reinhardii has been isolated that is deficient in inorganic carbon transport. This mutant strain, designated pmp-1-16-5K (gene locus pmp-1), was selected on the basis of a requirement of elevated CO2 concentration for photoautrophic growth. Inorganic carbon accumulation in the mutant was considerably reduced in comparison to wild type, and the CO2 response of photosynthesis indicated a reduced affinity for CO2 in the mutant. At air levels of CO2 (0.03-0.04%), O2 inhibited photosynthesis and stimulated the synthesis of photorespiratory intermediates in the mutant but not in wild type. Neither strain was significantly affected by O2 at saturating CO2 concentration. Thus, the primary consequence of inorganic carbon transport deficiency in the mutant was a much lower internal CO2 concentration compared to wild type. From these observations, we conclude that enzyme-mediated transport of inorganic carbon is an essential component of the CO2 concentrating system in C. reinhardii photosynthesis.