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Photo-induced pH Changes in the Vicinity of Isolated Peperomia metallica Chloroplasts

D. REMIŠ, A. A. BULYCHEV and G. A. KURELLA
Journal of Experimental Botany
Vol. 39, No. 202 (May 1988), pp. 633-640
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23691970
Page Count: 8
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Photo-induced pH Changes in the Vicinity of Isolated Peperomia metallica Chloroplasts
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Abstract

Photo-induced pH changes of the external medium in a region immediately adjacent to the surface of individual isolated Peperomia metallica chloroplasts have been measured using antimony pH-microelectrodes. The pH changes induced by continuous illumination were composed of two phases: an initial alkalization (phase I) and a subsequent acidification (phase II) of the medium. Both phases were severely suppressed by DCMU and protonophorous uncouplers but they showed different sensitivity towards DCCD, NH4Cl and some other agents. Phase I was selectively inhibited by DCCD and was partially restored upon addition of ATP to DCCD-poisoned chloroplasts. Phase II was inhibited by 1.0 mol m-3 NH4Cl. It appears from these data that phases I and II of light-induced pH changes are determined by different processes. It is suggested that the pH increase (phase I) is due to a photosynthetic CO2 fixation and the pH decrease (phase II) is caused by a light-dependent extrusion of protons from intact chloroplasts.

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