Internal Control of Stomatal Physiology and Photosynthesis. II. Photosynthetic Responses to Phaseic Acid

Abstract

Phaseic acid appears to act as a specific inhibitor of photosynthesis in vivo. Such inhibition is probably associated with the 'after-effects' of moisture stress and with other forms of non-stomatal influences on photosynthesis that follow manipulative treatments (leaf excision, fruit removal). This naturally occurring inhibitor was extracted from leaves of Vitis vinifera L. and applied to a variety of material (including vine foliage) under laboratory conditions. Photosynthetic activity of both excised leaves (CO2-H2O exchange; cuvette measurement) and tissue slices (oxygen electrode determinations) was strongly inhibited by buffered solutions at physiological concentrations. Phaseic acid inhibited oxygen evolution by isolated spinach chloroplasts (using ferricyanide as an electron acceptor) but had no effect on spinach leaf ribulosebisphosphate carboxylase activity. Photosynthetic regulation by phaseic acid might therefore relate to its influence over photosynthetic electron flow and generation of high energy metabolites which foster CO2 fixation.