@misc{oai:sucra.repo.nii.ac.jp:00010265,
 author = {青木, 直大},
 month = {},
 note = {In C4 photosynthesis, pyruvate uptake into mesophyll chloroplasts is an essential process. It has been known that [1] pyruvate is actively taken up into C4 mesophyll chloroplasts in a light-dependent manner, [2] as to a substitute for the light effect, a cation (Na+- or H+-) jump in the medium enhances pyruvate uptake in the dark, [3] C4 species can be divided into two groups, Na+-type or H+-type, due to the cation specificity, and [4] Na+/pyruvate cotransport is operating in Na+-type species. In this thesis, the mechanism of light-dependent active transport of pyruvate into mesophyll chloroplasts of C4 plants was studied. It consists of two parts.
Part 1: H+/pyruvate cotransport into mesophyll chloroplasts of H+-type C4 species and the role of phosphoenolpyruvate
Stromal pH of maize mesophyll chloroplasts was changed from 7 to 8 by illumination. A cotransport of pyruvate and H+ across the envelope of maize mesophyll chloroplasts was demonstrated in the light. 
1) The initial rate of H+ consumption in the external medium on addition of pyruvate was always quantitatively related with that of [14C]pyruvate uptake, namely one to one ratio of H+ and pyruvate uptake rates. These results indicate that pyruvate uptake in the light into mesophyll chloroplasts of H+-type C4 species is mediated by a cotransport mechanism of H+ and pyruvate.
2) H+ gradient across the envelope will be the driving force of H+/pyruvate cotransport into mesophyll chloroplasts of H+-type C4 species, since changes in the rate of pyruvate uptake under various pHs of the medium were closely correlated with the ΔpH formed across the envelope in the light.
3) Phosphoenolpyruvate (PEP) was transported together with H+ in C4 mesophyll chloroplasts via the phosphate translocator, in a manner similar to 3-phosphoglycerate transport in C3 chloroplasts
4) Both medium alkalization and stromal acidification on pyruvate addition in illuminated maize mesophyll chloroplasts were decreased in the presence of PEP. These results show that H+ influx accompanied with pyruvate import into illuminated mesophyll chloroplasts is compensated for with H+ efflux together with PEP export in H+-type C4 species. It suggests a role of PEP in maintaining the active pyruvate uptake during the photosynthesis.
Part 2: Active transport of pyruvate in the light and a possible role of Na+ gradient formation across the envelope in mesophyll chloroplasts of Panicum miliaceum L., a N a+-type C4 species
It has been thought without direct evidence that the driving force for Na+/pyruvate cotransport is Na+ gradient formed across the envelope by illumination, since Na+-jump in the dark induced pyruvate uptake in the
chloroplast. Actually, stromal pH and the amount of ATP are increased by illumination. Thus, ΔpH and/or ATP would be possible candidates of the driving force for the formation of Na+ gradient for active pyruvate transport into mesophyll chloroplasts of Na+-type C4 species. Rates of pyruvate uptake in the light and dark together with or without Na+-jump were compared under various pHs in the medium.
1) The light-dependent pyruvate uptake into mesophyll chloroplasts of P. miliaceum is correlated with stromal alkalization by illumination, but not with ΔpH formed across the envelope in the light.
2) Pyruvate uptake into mesophyll chloroplasts of P. miliaceum in the dark was not seen even in the presence of 10 mM Na+, while the activity was induced by Na+-jump or by illumination at external pH of 7.8. These induced activities showed similar patterns against the concentration of Na+. These results would indicate that illumination induces the formation of Na+ gradient across the envelope to drive Na+/pyruvate cotransport into mesophyll chloroplasts of Na+-type C4 species.
3) Pyruvate uptake due to the Na+ gradient across the envelope occurred independently of the pH in the medium. This suggests that Na+/H+ antiporter may not contribute to Na+ release from mesophyll chloroplasts of Na+-type C4 species.
4) Illumination and Na+-jump had a synergistic effect on the rate of pyruvate uptake at the medium pH from 7.4 to 8.2. At this pH range, some pyruvate uptake which was induced by H+-jump was observed even in mesophyll chloroplasts from Na+-type C4 species, but the rate was low compared with the effect of illumination and Na+-jump. Besides Na+ gradient, H+ gradient across the envelope may contribute in some extent to pyruvate uptake in alkaline pH range.
5) ATP content in mesophyll chloroplasts did not change by Na+-jump, negating a possible role of Na+-ATPase in the mesophyll chloroplast envelope of P. miliaceum., 主指導教官 : 金井龍二, text, application/pdf},
 title = {Studies on the Mechanism of Light-dependent Active Transport of Pyruvate into Mesophyll Chloroplasts of C4 Plants},
 year = {1996},
 yomi = {アオキ, ナオヒロ}
}