Relationship between light-induced potential change and internal ATP concentration in tonoplast-free Chara cells |
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Authors: | Kikuyama, Munehiro Hayama, Tomio Fujii, Sumiko Tazawa, Masashi |
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Affiliation: | Department of Biology, Faculty of Science, Osaka University Toyonaka, Osaka 560, Japan |
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Abstract: | The effect of the intracellular concentration of ATP ([ATP]1)on the light-induced potential change (LPC) in tonoplast-freeChara cells was studied. The LPC was hardly affected by loweringthe [ATP]1 by about 1/10 or by raising it to about 10 timesthe normal cytoplasmic concentration (0.51.3 mM). Theinsensitivity of LPC to [ATP]1 excludes the possibility thatan increase in [ATP]1 due to photosynthesis may induce the LPC.However, extreme lowering of the [ATP]1 to about 12 µMcompletely inhibited LPC, although photosynthetic O2 evolutionwas not significantly inhibited. This fact supports the hypothesisthat light stimulates the putative H+pump fueled by ATP. Theuncoupling agents DNP and CCCP greatly depolarized the membrane,and inhibited LPC strongly, but they did not decrease [ATP]1.Photosynthetic O2 evolution was inhibited to some extent by2 µM CCCP and strongly inhibited by 0.1 mM DNP. Sincethe membrane resistance increased significantly, these chemicalsare believed to act on the membrane as an inhibitor of the electrogenicH+ pump not as an H+conductor. Introduction of 1 mM ATP intocells treated with uncouplers, to a large extent restored theirability to produce LPC although the membrane potential in darknesswas maintained at a low level. 1Present address: Niigata College of Pharmacy, 5829 Kamishinei-cho,Niigata 950-21, Japan.2Present address: Department of Agricultural Chemistry, Collegeof Agriculture, Kyoto University, Kyoto 606, Japan.3Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan. (Received March 9, 1979; ) |
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