BOTH RUBISCO AND PHOSPHOENOLPYRUVATE CARBOXYLASE ARE BENEFICIAL FOR STOMATAL FUNCTION IN EPIDERMAL STRIPS OF COMMELINA-BENGHALENSIS

The relative importance of the Calvin cycle and beta-carboxylation, th rough phosphoenolpyruvate carboxylase (PEPC), pathways was assessed in relation to stomatal opening in epidermal strips of Commelina benghal ensis, using D,L-glyceraldehyde (an inhibitor of the Calvin cycle) and ichloro-2-dihydroxyphosphinoyl-methyl-2-propenoate (DCDP, an inhibito r of PEPC) or metabolites related to the Calvin cycle or PEPC. Stomata l 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, metabol ites related to not only PEPC (PEP or malate) but also the Calvin cycl e (R-5-P or PGA) relieved the inhibition of stomatal opening. We sugge st that both Calvin cycle and beta-carboxylation activity are benefici al for stomatal opening, particularly when either of these pathways is restricted. (C) 1997 Elsevier Science Ireland Ltd.