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

Abstract

Glycolate and ammonia excretion plus oxygen exchanges were measured in the light in l-methionine-dl-sulfoximine treated air-grown Chlamydomonas reinhardii. At saturating CO(2) (between 600 and 700 microliters per liter CO(2)) neither glycolate nor ammonia were excreted, whereas at the CO(2) compensation concentration (<10 microliters per liter CO(2)) treated algae excreted both glycolate and ammonia at rates of 37 and 59 nanomoles per minute per milligram chlorophyll, respectively. From the excretion values we calculate the amount of O(2) consumed through the glycolate pathway. The calculated value was not significantly different from the component of O(2) uptake sensitive to CO(2) obtained from the difference between O(2) uptake of the CO(2) compensation point and at saturating CO(2). This component was about 40% of stationary O(2) uptake measured at the CO(2) compensation point. From these data we conclude that glyoxylate decarboxylation in air-grown Chlamydomonas represents a minor pathway of metabolism even in conditions where amino donors are deficient and that processes other than glycolate pathway are responsible for the O(2) uptake insensitive to CO(2).