The photoregulation of H+ extrusion by hypocotyl segments of Cucumis sativus L. was studied. Irradiation with red light (to give Pfr) enhanced H+ efflux in the presence of Mg2+ and K+. This effect of red light was decreased by far red irradiation (to give Pr). The acidification was inhibited by sodium orthovanadate. These results imply that H+ extrusion is coupled to plasma membrane ATPase activity. In vivo pretreatment with filipin, which interferes with phytochrome association with membranes, reduced both photoregulation of ATPase activity and H+ extrusion. A similar effect was found after preirradiation with red light before a prolonged dark period at 4 °C, a treatment which is assumed to lower phytochrome levels.
- Cucumis sativus