Red and blue light-stimulated proton efflux by epidermal leaf cells of the Argenteum mutant ofPisum sativum

Abstract

Light stimulates leaf expansion in dicotyledons by increasing apoplastic acidification, cell wall loosening and solute accumulation for turgor maintenance. Red and blue light enhance growth via different photosystems, but the cellular location and modes of action of these systems is not known. Here, the effect of red and blue light was studied on transport processes in epidermal cells of expanding leaves of the Argenteum mutant of Pisvm sativum. Both red and blue light caused extracellular acidification by isolated epidermal tissue, which was stimulated by extracellular K+ and inhibited by DCCD at 0.1 mol m(-3). Acidification induced by red compared with blue light showed different saturating kinetics in fluence rate-response curves. Under near saturating light conditions the effects of red and blue light were additive. The red light-induced acidification was inhibited by far-red light while the blue light-induced acidification was not. Light caused a hyperpolarization of the membrane potential in epidermal strips, and stimulated Rb-86(+) uptake by epidermal protoplasts. These results show that phytochrome and an additional blue light-photoreceptor function in isolated epidermal cells to promote proton efflux, hyperpolarization, and cation uptake.