Light-Dependent Uptake of Pyruvate by Mesophyll Chloroplasts of a C_4 Plant, Panicum miliaceum L.

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概要

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• Light-dependent active uptake of pyruvate was reported in mesophyll chloroplasts of a C_4 plant, Panicum miliaceum [Ohnishi and Kanai (1987) Plant Cell Physiol. 28: 1]. The present study tried to clarify the energy source of this active uptake. Preillumination of the mesophyll chloroplasts increased over tenfold their pyruvate uptake in the light and dark. This indicates that light itself is not essential for the enhancement. The pyruvate uptake capacity (the initial uptake rate) of the mesophyll chloroplasts increased on illumination and reached a steady-state level after a few minutes; this rise was faster under higher light intensities. When the chloroplasts were returned to darkness, the uptake capacity decayed with a half-life of about 1 min; this was independent of the light intensity of preillumination. Illumination of the chloroplasts also increased the stromal pH from about 7 to 8 and the stromal ATP level from about 5 to 15-25 nmol・(mg chl)^<-1>. The change of the former during dark-to-light and light-to-dark transitions occurred within 2 to 5 min, while the change of the latter took place much faster within 1 min. The steady-state levels of the pyruvate uptake capacity and stromal pH were saturated at a light intensity of 3 μE・m^<-2>・s^<-1>, while the ATP level increased with a further increase in the light intensity. The former two parameters also showed similar sensitivity to the inhibition by carbonylcyanide-m-chlorophenylhydrazone, while a higher concentration of the inhibitor was needed to reduce the ATP level. Nitrite at 4 mM inhibited the light-dependent pyruvate uptake and stromal alkalization but had little effect on the stromal ATP level, while 2 mM arsenate decreased the stromal ATP without significant effects on pyruvate uptake and stromal pH. The good correlation of pyruvate uptake and stromal pH suggests that the active pyruvate uptake by the mesophyll chloroplasts is primarily driven by the pH gradient across the envelope.

• 日本植物生理学会の論文

著者

• Kanai Ryuzi

  Department Of Biochemistry And Molecular Biology Faculty Of Science Saitama University

• Ohnichi Jun-ichi

  Department of Biochemistry, Faculty of Science, Saitama University

• Ohnichi Jun-ichi

  Department Of Biochemistry Faculty Of Science Saitama University

関連論文

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