Ca2+ uptake and plasma membrane depolarization associated with blue light-sensitive exogenous NADH oxidation by Cuscuta protoplasts

Protoplasts isolated from the apical segments of Cuscuta reflexa exhibited blue light-sensitive PM-linked NADH oxidase activity and increased rate of Ca2+-uptake in presence of NADH in dark, which was also stimulated by blue light. Contrary to marginal inhibition by Con A treatment, the ATPase inhibitors significantly inhibited the Ca2+ uptake by the protoplasts both in dark and under blue light. The Ca2+-calmodulin antagonists, W-7 and calmidazolium, also inhibited Ca2+-uptake by protoplasts under similar conditions. The state of PM polarization was monitored by the fluorescent dye 9-amino acridine. It was observed that PM-linked NADH oxidation caused hyperpolarization of the membrane, the exposure of which to blue light resulted in membrane depolarization. The presence of Ca2+-calmodulin antagonists or Con A treatment completely abolished the blue light-induced membrane depolarization. It is argued that these actities at the PM, having some glycoproteic components, are functionally closely involved in blue light-induced signal transduction in Cuscuta