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 degrees C. Whereas nonconditional mutants required acetate for growth at both 25 and 35 degrees C, the conditional mutants have normal photoautotrophic growth at 25 degrees C. The conditional mutants consisted of two classes: (a) Temperature-sensitive mutants died under all growth conditions at 35 degrees C, but (b) temperature-sensitive, acetate-requiring mutants were capable of heterotrophic growth at 35 degrees 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.