Comparison of the effects of ammonia and methylamine on chloride transport and intra cellular ph in chara corallina

Smith, F.A.

Journal of Experimental Botany 31(121): 597-606


ISSN/ISBN: 0022-0957
Accession: 005013834

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Ammonium and methylammonium ions greatly increase the rate of Cl- transport in C. corallina. This effect is dependent on the pH of the bathing solution. The amine-stimulated Cl- influx is small at pH 5.5, increases to a maximum at pH 6.5-7.5, and decreases again as the pH is raised to 8.5. Increased Cl- influx is accompanied by an increase in cytoplasmic pH, as calculated from the distribution of 5,5-dimethyloxazolidine-2,4-dione. When the external pH lies between 5.5 and 7.3, cytoplasmic pH in the absence of amine is 7.65-7.70, with an increase of 0.15-0.25 in the presence of amine. As external pH is increased above 7.3, cytoplasmic pH also increases, with progressively less effect to amine. Although the relationship between Cl- influx and cytoplasmic pH is not simple, the results provide evidence in accord with the hypothesis that Cl- transport in Chara involves H+-Cl- symport, or the equivalent OH--Cl- antiport. The possible role of cytoplasmic pH as a factor involved in the regulation of membrane transport in Chara is discussed.