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Plant and Cell Physiology, 1994, Vol. 35, No. 5 801-806
© 1994

Proton/Pyruvate Cotransport into Mesophyll Chloroplasts of C4 Plants

Naohiro Aoki, Jun-ichi Ohnishi and Ryuzi Kanai

Department of Biochemistry, Faculty of Science, Saitama University Urawa, 338 Japan

Light-enhanced active pyruvate uptake into mesophyll chloroplasts of C4 plants 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 C4 species 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 C4 mesophyll 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 mays L. and Coix lacryma-jobi L., but not in those from Na+-type species Panicum miliaceum L., Setaria italica (L.) Beauv. and Panicum maximum Jacq. The initial rate of H+ consumption showed good correlation with [14C]pyruvate uptake measured by silicone oil filtering centrifugation, both being inhibited by N-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 C4 species in the light.

(Received January 5, 1994; Accepted May 6, 1994)
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