Blue light-sensitive plasma membrane bound exogenous NADH oxidase in Cuscuta reflexa

Protoplasts isolated from Cuscuta reflexa exhibited a higher rate of exogenous NADH oxidation as compared to NADPH in the dark. NAD(P)H oxidation was monitored by measuring the rate of oxygen consumption and this oxidase system was sensitive to blue light. Both NADH oxidase and its blue light sensitivity were inhibited by -SH group reacting agents. The corresponding changes occurring in H+-extrusion activity and intracellular ATP levels were also monitored. Stimulation of NADH oxidation under blue light corresponded to increased rate of H+-extrusion and intracellular ATP level, the converse was also true under NADH oxidase inhibitory conditions. These observations suggested a close functional association between blue light-sensitive plasma membrane bound redox activity and H+-ATPase in this tissue. Further, concanavalin A binding of protoplasts resulted in a loss in NADH oxidase activity and its blue light sensitivity suggesting apoplastic location and glycoprotein nature of the blue light sensitive NADH oxidase system in Cuscuta.