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Intra cellular ph regulation in the giant celled marine alga chaetomorpha darwinii



Intra cellular ph regulation in the giant celled marine alga chaetomorpha darwinii



Journal of Experimental Botany 31(124): 1357-1370



The vacuolar pH (pHv) and the cytoplasmic pH (pHc) of the marine giant-celled green alga C. darwinii were measured by pH microelectrode techniques on extracted vacuolar sap, and by the [14C]DMO [5',5'-dimethyloxazolidine 2,4-dione] distribution method, respectively. Equilibration of DMO occurred with a half-time of about 2 h, with an apparent PDMO of 3.6 .times. 10-5 cm s-1, but the vacuolar concentration of free, undissociated DMO was always less than the external concentration. The explanation offered for freshwater giant-celled algae of net DMO- leakage across the plasmalemma cannot apply to C. darwinii, since electrically-driven DMO- exit from the cytoplasm should be similar across the plasmalemma and the tonoplast in these cells with large, vacuole-positive potential differences across the tonoplast. pHc was accordingly computed assuming either tonoplast or plasmalemma equilibration of DMO, with correction for DMO metabolism within the cell. pHc was 8.0-8.3 in the light in artificial seawater (pHo about 8.0), was some 0.5 U lower in the dark, and was slightly lower with an external pH of 7. Vacuolar pH was 6.5-6.9, without consistent effects of illumination or of external pH of 7 rather than 8. While .DELTA.hivin.mu.H+ at the tonoplast was similar to that in giant-celled freshwater algae (although with a greater contribution from .DELTA.psi. relative to .DELTA.pH), .DELTA.hivin.mu.H+ at the plasmalemma was less than 8 kJ mol-1, i.e., less than 1/3 of the value in freshwater green algae. .DELTA.hivin.mu.Na+ was 13 kJ mol-1 at the plasmalemma. The possibility that the primary active transport process at the plasmalemma of C. darwinii (and certain other marine algae) is Na+ efflux rather than H+ efflux is discussed.

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