REGULATION OF BIOSYNTHESIS OF CHLOROPHYLL PRECURSORS IN MUTANTS OF THE GREEN-ALGA CHLAMYDOMONAS-REINHARDTII

The chlorophyll-deficient nuclear gene chl1 mutant of the green alga Chlamydomonas reinhardtii accumulates protoporphyrin IX (PP), which gives a brown-yellow color to the colony. In chl1-mutant cells, protochlorophyllide (Pchlde) accumulation is decreased, while delta-aminolevulinic acid (ALA)-synthesizing activity is increased A double mutant chl1 mod-u-25 was isolated whose cells accumulate 20 times more PP than those of the parent strain and form dark-brown colonies. The regulatory mutation mod-u-25 increases two-fold the ALA-synthesizing activity and results also in an enhancement of the Pchlde and chlorophyllide content in comparison with the wild strain. The ALA-synthesizing enzymes from the single (chil1) and double (chl1 mod-u-25) mutants as well as from the wild strain are equally sensitive to heme inhibition. In the double mutant protoheme synthesis is unimpaired Some peculiarities of chlorophyll biosynthesis regulation in the chl1 mod-u-25 double mutant of C. reinhardtii are discussed