[On the induction of nitrate- and nitrite-reductase in synchronized Chlorella cultures]

Nitrate- and nitrite-reductase (E.C. 1.6.6.1. and E.C. 1.6.6.4.) activities were determined during the light-dark changes in two completely synchronized Chlorella strains. A sharp increase of both enzyme activities during the first light hour was found in Chl. vulgaris forma tertia, a smaller one in Chl. pyrenoidosa. The rise in enzyme activity could only be inhibited by actidione but not by antibiotics which inhibit plastidic protein synthesis. It can therefore be concludet that light causes a de novo synthesis of both enzymes on cytoplasmic ribosomes. It is assumed that light effects a release of substances to the cytoplasm, probably formed during CO2-fixation, which can effect a cytoplasmic protein synthesis.