Interactions between photosynthesis and respiration in the green alga Chlamydomonas reinhardtii. Characterization of light-enhanced dark respiration

The rate of respiratory O{dollar}sb2{dollar} consumption by Chlamydomonas reinhardtii cell suspensions was greater after a period of photosynthesis than in the preceding dark period. This "light-enhanced dark respiration" (LEDR) was a function of both the duration of illumination and the photon fluence rate. LEDR was insensitive to inhibition by the alternative oxidase inhibitor propyl gallate, suggesting that it was mediated by the cytochrome pathway. Mass spectrometric measurements of gas exchange indicated that the rate of respiratory O{dollar}sb2{dollar} consumption increased during photosynthesis, while respiratory CO{dollar}sb2{dollar} production a decreased, in a photon fluence rate-dependent manner. The rate of post-illumination O{dollar}sb2{dollar} consumption provided good measure of the O{dollar}sb2{dollar} consumption rate in the light. LEDR was substantially decreased by the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or glycolaldehyde, suggesting that LEDR was photosynthesis-dependent. The onset of photosynthesis resulted in an increase in cellular levels of phosphoglyceraldehyde, malate and phosphoenolpyruvate, and a decrease in whole cell ATP and citrate levels; all of these changes were rapidly reversed upon darkening. The onset of photosynthesis also resulted in an approximately 20% decrease in pyruvate dehydrogenase complex activity. Light inhibition could be prevented by prior addition of DCMU. Addition of the Calvin cycle inhibitor glycolaldehyde also prevented the light-induced inhibition of PDC activity. Light inhibition of PDC activity was 50% reversed after 5 min of darkness. These results are consistent with a decrease in the rate of respiratory carbon flow to the TCA cycle during photosynthesis, whereas the increase in respiratory O{dollar}sb2{dollar} consumption during photosynthesis may be mediated by the export of photogenerated reductant from the chloroplast. We suggest that photosynthesis interacts with respiration at more than one level, simultaneously decreasing the rate of respiratory carbon flow while increasing the rate of respiratory O{dollar}sb2{dollar} consumption.