The regulation of ammonia uptake inChara australis

Abstract

The regulation of ammonia uptake was investigated in internodal cells of the freshwater alga Chara australis. Ammonia uptake was estimated by monitoring (i) its depletion from the bathing solution, (ii) the uptake of radiolabelled methylamine, an analogue of ammonia, and (iii) depletion of ammonia in the unstirred layer with the microelectrode ion-flux estimation technique (MIFE). Distribution of methylamine ( 14 CH 3 NH 3 + ) between the vacuole and cytoplasm was estimated with efflux analysis. When cells were bathed continuously in solutions containing ammonia or methylamine, the uptake rates of both amines decreased over 12 to 48 h despite the continuing existence of a large electrochemical gradient favouring influx of the NH 4 + and CH 3 NH 3 + cations