Photoinduced H+ transport between chloroplasts and the cytoplasm in a protoplasmic droplet of Characeaeстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The effects of light on the membrane potential and cytoplasmic pH of isolated droplets of protoplasm from Nitella have been studied using microcapillary electrodes and pH-sensitive antimony micro-electrodes. Illumination of chloroplast-containing droplets caused a change of the membrane potential with a concomitant acidification of both the cytoplasm and the outer medium, but it had no effect on the electrical resistance of the surface membrane. Treatment of protoplasmic droplets with uncouplers (NH4Cl and CCCP) resulted in a complete inhibition of the light-induced acidification of the cytoplasm, whereas the energy transfer inhibitor DCCD had no effect. A correlation between the formation of a pH gradient across the thylakoid membrane and the acidification of the cytoplasm was explicable in terms of the assumption of restricted spatial communication between the intra-thylakoid volume and the cytoplasm in intact chloroplast. The photo-induced acidification of the boundary layer of an external medium was markedly stimulated under the action of inhibitors of H+-ATPase DCCD and DES. These findings suggest that the active extrusion of H+ from the cytoplasm into the external medium is not driven by an ATPase, although H+-conducting channels of membrane ATPase provide a pathway for a passive diffusion of protons from outside into the cytoplasm