Temperature-Sensitive, Photosynthesis-Deficient Mutants of Chlamydomonas reinhardtii

Mutants of the unicellular, green alga Chlamydomonas reinhardtii were recovered by screening for the absence of photoautotrophic growth at 35°C. Whereas nonconditional mutants required acetate for growth at both 25 and 35°C, the conditional mutants have normal photoautotrophic growth at 25°C. The conditional mutants consisted of two classes: (a) Temperature-sensitive mutants died under all growth conditions at 35°C, but (b) temperature-sensitive, acetate-requiring mutants were capable of heterotrophic growth at 35°C when supplied with acetate in the dark. The majority of mutants within the latter of these two classes had defects in photosynthetic functions. These defects included altered pigmentation, reduced whole-chain electron-transport activity, reduced ribulosebis-phosphate carboxylase activity, or pleiotropic alterations in a number of these photosynthetic components. Both nuclear and chloroplast mutants were identified, and a correlation between light-sensitive and photosynthesis-deficient phenotypes was observed.