Light-induced changes in membrane potential in Spirogyra

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Spirogyra cells exhibited changes in membrane potential when they were exposed to light. Cells made chloroplast-free did not show any light-induced potential change (LPC) upon illumination with white light and also monochromatic red (680 nm) and far red (720 nm) light. LPC was observed when the cell contained only a small fragment of chloroplast, whether the cell had a nucleus or not. The magnitude of LPC depended on the amount of chloroplast in the cell. DCMU at 10^<-5> M, CCCP at 10^<-5> M and DNP at 10^<-4> M at pH 5.5 suppressed LPC, while CCCP at 1-5×10^<-6> M, NH_4Cl at 5×10^<-2> M and DNP at 10^<-4> M at pH 7.0 stimulated LPC. PMS at 10^<-4> M stimulated LPC and could induce LPC which was completely inhibited by DCMU. These facts suggest that LPC is related to noncyclic and cyclic electron flows. The influences of light and dark conditions and various metabolic inhibitors (DCMU, DNP, CCCP, NH_4Cl) on ATP level have been investigated. No significant difference in the ATP level was observed between cells in the light and dark. DNP at 10^<-4> M (pH 5.5) and CCCP at 5×10^<-6> M decreased the ATP level significantly, while DCMU and NH_4Cl only slightly. Good correlation was not found between the total ATP level and LPC in Spirogyra. LPC occurred even when the external medium contained only a single salt such as KCl, NaCl or CaSO_4. LPC was also recorded in chloroplasts in situ and in vitro. The mode of LPC of chloroplasts was quite different from that of the cell. On illumination, the chloroplast potential changed very rapidly and transiently in the positive direction then recovered spontaneously to almost the original potential level. Possible causes of LPC are discussed in relation to the electrogenic ion pump.
日本植物生理学会の論文

Light-induced changes in membrane potential in Spirogyra

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