Relationship between light-induced potential change and internal ATP concentration in tonoplast-free Chara cells

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The effect of the intracellular concentration of ATP ([ATP]_i) on the light-induced potential change (LPC) in tonoplast-free Chara cells was studied. The LPC was hardly affected by lowering the [ATP]_i by about 1/10 or by raising it to about 10 times the normal cytoplasmic concentration (0.5-1.3 m_M). The insensitivity of LPC to [ATP]_i excludes the possibility that an increase in [ATP]_i due to photosynthesis may induce the LPC. However, extreme lowering of the [ATP]_i to about 1-2 μ_M completely inhibited LPC, although photosynthetic O_2 evolution was not significantly inhibited. This fact supports the hypothesis that light stimulates the putative H^+-pump fueled by ATP. The uncoupling agents DNP and CCCP greatly depolarized the membrane, and inhibited LPC strongly, but they did not decrease [ATP]_i. Photosynthetic O_2 evolution was inhibited to some extent by 2 μ_M CCCP and strongly inhibited by 0.1 m_M DNP. Since the membrane resistance increased significantly, these chemicals are believed to act on the membrane as an inhibitor of the electrogenic H^+ pump not as an H^+ conductor. Introduction of 1 m_M ATP into cells treated with uncouplers, to a large extent restored their ability to produce LPC although the membrane potential in darkness was maintained at a low level.
日本植物生理学会の論文