Proton extrusion by leaf discs ofVicia faba L.: light- and ion-stimulated H(su+) release†

Abstract

Previous electrophysiological and tracer kinetic studies indicated that the uptake of neutral amino acids took place by means of the proton cotransport mechanism in the leaf tissue of broad bean plants. The present investigations were designed to characterize the origin of the driving force for this process, and the proton pumping activity of leaf cells ofVicia. This activity is known to be revealed when peeled broad been leaf discs, floated on a bathing solution in the light or in darkness acidify the medium. White light caused the strongest acidification. The presence of K+ and Na+ in the external solution increased the H+ secretion significantly, whereas addition of Ca++caused only an insignificant enhancement of proton extrusion. The inhibitors of photosynthetic electron transport DCMTJ (50 μM) and nitrofen (50 μM) eliminated the light-enhanced H+ release indicating the dependence on photosynthesis. The involvement of a proton pump was evidenced by the effects of the uneoupler CCCP, the SH reagent HgCl2 and the ATPase inhibitor orthovanadate. The experimental results support the conclusion that H+ extrusion byVicia leaf cells is an active electrogenic process requiring metabolic energy. In the light this energy requirement is suppliedvia photosynthetic electron transport.