Both rubisco and phosphoenolpyruvate carboxylase are beneficial for stomatal function in epidermal strips of Commelina benghalensis

Abstract

The relative importance of the Calvin cycle and β-carboxylation, through phosphoenolpyruvate carboxylase (PEPC), pathways was assessed in relation to stomatal opening in epidermal strips of Commelina benghalensis, using D,L-glyceraldehyde (an inhibitor of the Calvin cycle) and 3,3- dichloro-2-dihydroxyphosphinoyl-methyl-2-propenoate (DCDP, an inhibitor of PEPC) or metabolites related to the Calvin cycle or PEPC. Stomatal opening was markedly inhibited by both DCDP and D,L-glyceraldehyde. In the absence of these inhibitors, exogenous metabolites such as PEP or ribose-5-P (R-5-P) had little or no effect on stomatal opening. On the other hand, in the presence of DCDP or D,L-glyceraldehyde, metabolites related to not only PEPC (PEP or malate) but also the Calvin cycle (R-5-P or PGA) relieved the inhibition of stomatal opening. We suggest that both Calvin cycle and β-carboxylation activity are beneficial for stomatal opening, particularly when either of these pathways is restricted.