Accumulation of zeta-carotene in Chlamydomonas reinhardtii under control of the ac5 nuclear gene

The accumulation of different precursors of carotenoid biosynthesis in caro tenoid-deficient mutants of Chlamydomonas reinhardtii was studied by HPLC-a nalysis. zeta-Carotene accumulated in several ac5 mutants, this character c osegregated with mutations in the ac5 gene. Two groups of ac5 mutants diffe ring in zeta-carotene accumulation were distinguished. One (ac5-1) accumula ted zeta-carotene in the dark but not in the light. The other (ac5-2) accum ulated zeta-carotene under both dark and light conditions, ac5-2 strains ac cumulated more zeta-carotene in the dark than ac5-1 strains. Genetic data s uggested that the mutations ac5-1 and ac5-2 were allelic. Pleiotropic effec ts of mutations in the ac5 gene included decreased levels of chlorophyll a and b and acetate requirement. The results are consistent with the presence of a defective zeta-carotene desaturase in ac5 mutants.