Glutathione-dependent rate limitation in the CO₂ fixation

Abstract

Glutathione is a ubiquitous tripeptide that is synthesized via two reactions dependent on photosynthetic ATP production. In this study, we used Arabidopsis mutants having low levels of glutathione to evaluate the relationship of glutathione with a key Calvin-cycle enzyme, Rubisco. Compared to wild-type plants, these mutants showed 80-90% CO₂ assimilation rates per unit leaf area and 80-90% Rubisco activation state, but they showed no significant difference in Rubisco activity per unit leaf area. Taken together, the decrease in glutathione levels reduces the Rubisco activation state but the glutathione deficiency-dependent decrease in the CO₂ fixation is attributed to any other glutathione-regulated factor than Rubisco. Since the Calvin cycle enzyme aldolase is regulated by glutathione, it is considered that low glutathione levels restrict aldolase activity and resultantly decrease the CO₂ assimilation rate. We will discuss relationship of glutathione levels to aldolase as well as Rubisco on the Calvin cycle regulation.