Hydroxyl– and Bicarbonate-Associated Transport Processes inChara corallina:Studies on the Light-Dark Regulation Mechanism

Lucas, W. J. and Ogata, K. 1985. Hydroxyl– and bicarbonate–associated transport processes in Chara corallintr. Studies on the light–dark regulation mechanism.—J. exp. Bot. 36: 1947–1958. Experiments were undertaken on the fresh water alga Chara corallina to investigate the nature of the coupling between the chloroplasts and the light–dependent OH− and HCO3- -associated plasmalemma transport systems. Electrophysiological experiments, in which DCMU was employed, revealed that this chemical could elicit a hyperpolarization of the membrane potential that was identical to that normally obtained by turning off the light. This DCMU–induced hyperpolarization was obtained under control (⁠+HCO3-⁠) and phosphate–decoupled conditions (⁠-HCO3--HCO3--HCO3--HCO3-⁠). Measurements of the extracellular electric potentials which are associated with the acidic (⁠HCO3-⁠) and alkaline (OH−) regions, indicated that, in the presence of control (⁠-HCO3-⁠)or phosphate–decoupled conditions, normal profiles were established under air, oxygen or nitrogen environments. These results indicate that the generation of the control signal(s) is related to events associated with chloroplast electron transport, rather than to changes in the flow or levels of carbon intermediates within the reductive pentose phosphate or photorespiratory cycles. Although the level of oxygen was found to have no effect on the light–induced activation of the OH regions, we found that in pure oxygen the dark–induced inactivation of the OH− efflux system was delayed, and that partial transport function could be maintained in the dark. The possible involvement of changes in either the ratio of oxidized to reduced ferridoxin or NADP± to NADPH, as part of this light–mediated control signal, is discussed.