Light-Dependent Oxygen Uptake, Glycolate, and Ammonia Release in l-Methionine Sulfoximine-Treated Chlamydomonas

Abstract

Glycolate and ammonia excretion plus O2 exchanges were measured in the light in L-methionine-DL-sulfoximine treated air-grown C. reinhardii. At saturating CO2 (between 600 and 700 .mu.l/l CO2) neither glycolate nor ammonia were excreted, whereas at the CO2 compensation concentration (< 10 .mu.l/l CO2) treated algae excreted both glycolate and ammonia at rates of 37 and 59 nmol min-1 mg-1 chlorophyll, respectively. From the excretion values the amount of O2 consumed through the glycolate pathway was calculated. The calculated value was not significantly different from the component of O2 uptake sensitive to CO2 obtained from the difference between O2 uptake of the CO2 compensation point and at saturating CO2. This component was .apprx. 40% of stationary O2 uptake measured at the CO2 compensation point. Glyoxylate decarboxylation in air-grown Chlamydomonas apparently represents a minor pathway of metabolism even in conditions where amino donors are deficient and processes other than glycolate pathway apparently are responsible for the O2 uptake insensitivity to CO2.