Proton/Pyruvate Cotransport into Mesophyll Chloroplasts of C4Plants

摘要

Light-enhanced active pyruvate uptake into mesophyll chloroplasts of C4plants was reported to be mimicked by either of the two types of cation jump: H+-jump in maize and phylogenically related species (H+-type) and Na+-jump in all the other C4species tested (Na+-type) [Aoki, N., Ohnishi, J. and Kanai, R. (1992)Plant Cell Physiol. 33: 805].In this study, medium and stromal pH was monitored in the suspension of C4mesophyll chloroplasts. Medium alkalization lasting for 5 to 10 seconds after pyruvate addition was detected by a pH electrode and observed only in the light and only in mesophyll chloroplasts from H+-type species,Zea maysL. andCoix lacryma-jobiL., but not in those from Na+-type speciesPanicum miliaceumL.,Setaria italica(L.) Beauv. andPanicum maximumJacq. The initial rate of H+consumption showed good correlation with [14C]pyruvate uptake measured by silicone oil filtering centrifugation, both being inhibited byN-ethylmaleimide and 7-chloro-4-nitrobenzo-2-oxa-l,3- diazole to the same degree. The ratio of the rate of H+uptake to that of pyruvate uptake was always about 1. Pyruvate-induced acidification of the stroma was observed in maize mesophyll chloroplasts. These results show one to one cotransport of H+and pyruvate anion into mesophyll chloroplasts of H+-type C4species in the light.