Plasmalemma Transport of OH in Chara corallina: III. FURTHER STUDIES ON TRANSPORT SUBSTRATE AND DIRECTIONALITY.

The identity of the plasmalemma-transported species that develops the alkaline bands of Chara corallina was investigated. The effect of fusicoccin on the rate of HCO(3) (-) assimilation, and on the time-dependent alkaline band pH buildup following low pH flushing, was found to be small, with no stimulatory effect. Computer simulation of the flushing experiments showed that in the experimental situation the alkaline band transport system was slowed down, rather than speeded up, by low pH flushing. A detailed theoretical examination of the maximum rate of proton production from water showed that measured alkaline band fluxes are too large to be explicable in terms of an H(+) influx system. The experimental and theoretical results indicate that the plasmalemma transport of OH(-) ions is responsible for the measured negative external electric potential and alkalinity flux which are associated with the alkaline band phenomenon. Consequently, HCO(3) (-) influx across the characean plasmalemma must be charge-balanced by the efflux of OH(-) ions.