Light-dependent Redistribution of Ions in Isolated Spinach Chloroplasts

Abstract

The Mg²⁺, K+ and Cl- contents of chloroplast pellets collected after centrifugation in light and dark conditions have been determined in a specific reaction medium at pH 7.8 and 6.6. It was found that the light-induced proton uptake by chloroplasts was electrically balanced mainly by Mg²⁺ efflux and to a lesser extent by K⁺ efflux. Unlike results in other studies, Cl^- influx was rather small.

A model for the ionic relations of envelope-free chloroplasts is considered. Light-induced changes in the ionic contents calculated from the model are in agreement with our observations. An attempt is made to apply similar considerations to another set of reported data.