PHYSIOLOGICAL AND HERITABLE CHANGES IN CYCLIC AMP LEVELS ASSOCIATED WITH CHANGES IN FLAGELLAR FORMATION IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA)1

ABSTRACT Synchronously dividing cells of Chlamydomonas reinhardtii Dang. (Chlorophyta) produce a single peak of cyclic adenosine monophosphate (cAMP), about sevenfold above the basal level, at the time of onset of the flagellar shortening that precedes mitosis. Cultures of a spontaneous palmelloid variant (which forms flagella‐less cell clusters) of C. reinhardtii produce up to 15 times more cAMP per gram fresh weight of cells than do cultures of normal C. reinhardtii. Revertants from the palmelloid phenotype to the normal phenotype exhibit the low levels of cAMP characteristic of normal C. reinhardtii. Thus, elevation of cAMP level and decreased ability to form or maintain flagella are closely related phenomena. We propose that flagellar assembly/disassembly is regulated by endogenous cAMP in C. reinhardtii .