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

Département de Biologie, Service de Radioagronomie, Cen de Cardarache, B.P. No. 1, F-13115 Saint-Paul-lez-Durance, France

Glycolate and ammonia excretion plus oxygen exchanges were measured in the light in L-methionine-DL-sulfoximine treated air-grown Chlamydomonas reinhardii. At saturating CO₂ (between 600 and 700 microliters per liter CO₂) neither glycolate nor ammonia were excreted, whereas at the CO₂ compensation concentration (<10 microliters per liter CO₂) 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 O₂ consumed through the glycolate pathway. 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 about 40% of stationary O₂ uptake measured at the CO₂ 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 O₂ uptake insensitive to CO₂.