Circulating electric currents between acid and alkaline zones associated with bi carbonate assimilation in chara corallina

Walker, N.A.; Smith, F.A.

Journal of Experimental Botany 26(106): 1190-1206


ISSN/ISBN: 0022-0957
Accession: 004959996

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Some charophyte species, like some other freshwater plants, were shown to take up .**GRAPHIC**. for photosynthetic fixation. Such plants show localized deposits of CaCO3 associated with localized OH- excretion. C. corallina produces acid and alkaline regions in unbuffered external media, in the light, even when CaCo3 is not being precipitated. These regions are associated with .**GRAPHIC**. uptake and OH- efflux, respectively. Large currents were found to circulate, in the light, between acid and alkaline zones of Chara internodes, by direct measurement of the short-circuit current and measurement of potential differences in the solution around the cell. Both methods suggest currents of 0.5-1 .mu.A per zone, with local current densities of about 75 mA m-2, or local univalent fluxes of 0.75 .mu.mol m-2 s-1. These circulating currents produce mean peak-to-peak potential differences of 7 mV in the external medium. The fluxes are believed to be of .**GRAPHIC**. and H+ or OH-. While active transport of .**GRAPHIC**. is strongly indicated, passive uniport of H+ or OH- appears to be sufficient. Control systems for both fluxes would be required.