CHLOROPLAST RESPIRATION IN CHLORELLA-PYRENOIDOSA CALU-175 - EFFECTS OF NITROGEN DEFICIENCY, EXOGENOUS GLUCOSE, AND ELEVATED-TEMPERATURE

The rate of chloroplast respiration in Chlorella was studied with resp ect to some changes in the physiological state induced by nitrogen def iciency, heterotrophic growth, and incubation at supraoptimal temperat ure. Iodoacetamide (an inhibitor of glycolysis), salicylhydroxamate (a n inhibitor of nonmitochondrial respiration), and 2-deoxy-D-glucose (a nonmetabolizable analogue of glucose), inhibited the respiration of c hloroplasts. Treatments that inactivate photosystem II (PS II), i.e., the addition of glucose, nitrogen deprivation, or dark incubation at e levated temperatures (39-43 degrees C), drastically (8-10 times) incre ased the rate of chloroplast respiration. In the absence of CO2, no en hancement of chloroplast respiration was recorded in nitrogen-starved cells. Cycloheximide, an inhibitor of cytoplasmic protein synthesis, a nd 2-deoxy-D-glucose prevented the increase in the chloroplast respira tion rate caused by the addition of glucose or incubation at elevated temperatures. It is suggested that the inhibition of PS II, previously described in Chlorella incubated for a long time at supraoptimal temp erature, is associated with the enhancement of chloroplast respiration .