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 C hlamydomonas reinhardtii accumulates protoporphyrin IX (PP), which giv es a brown-yellow color to the colony. In chl1-mutant cells, protochlo rophyllide (Pchlde) accumulation is decreased, while delta-aminolevuli nic acid (ALA)-synthesizing activity is increased A double mutant chl1 mod-u-25 was isolated whose cells accumulate 20 times more PP than th ose 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 conte nt in comparison with the wild strain. The ALA-synthesizing enzymes fr om the single (chil1) and double (chl1 mod-u-25) mutants as well as fr om the wild strain are equally sensitive to heme inhibition. In the do uble mutant protoheme synthesis is unimpaired Some peculiarities of ch lorophyll biosynthesis regulation in the chl1 mod-u-25 double mutant o f C. reinhardtii are discussed