Light-dependent volume changes and reactions in chloroplasts. I. Action of alkenylsuccinic acids and phenylmercuric acetate and possible relation to mechanisms of stomatal control.

Abstract

Light (electron flow) and energy-dependent mechanisms that control the movement of water and ions in spinach chloroplasts are known. Since these processes may be involved in stomatal control, the action of certain substances that cause their closure in plants was examined on spinach chloroplasts in vitro. Phenylmercuric acetate and alkenylsuccinic acids inhibited light-induced chloroplast swelling which occurred by an energy-independent mechanism. Light-induced shrinkage of chloroplasts, an energy-dependent mechanism, was also inhibited by the alkenylsuccinic acids, but phenylmercuric acetate exerted a stimulation of the light effect. An examination of the action of these substances on electron flow (NADP reduction) and photophosphorylation revealed that these reactions are inhibited. A scheme illustrating the relation between electron flow systems in chloroplasts to volume changes and the site of action of the substances examined is presented. An explanation for the mechanism of stomatal control based upon the regulation of chloroplast volume by light- and energy-dependent processes is proposed.