Ion Transport and the Effects of Acetic Acid in White Clover

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Abstract
Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transport and the effects of acetic acid in white clover. I. Phosphate absorption.—J. exp. Bot. 39: 79–88. The effect of acetic acid on phosphate absorption by white clover tissue has been examined. At 1·0 mol m3 acetic acid phosphate absorption by roots of intact plants was stimulated by 36% (P < 0.001). At 5.0 and 10 mol m−3 acetic acid there was marked inhibition of absorption by both suspension cultures of cells and the roots of intact plants. The inhibition was pH dependent with decreasing pH causing increased inhibition. Acetic acid caused changes in the membrane electropotential (ΔE) with concentrations of 2·0 mol m−3 or less causing persistent polarization whereas at 5·0 mol m−3 and higher concentrations the polarization was followed by a greater depolarization. Intracellular pH as measured by the fluorescence of fluorescein was lowered by acetic acid. Calculations indicate that for white clover roots the proton motive force (pmf) appears to provide sufficient energy for phosphate absorption. It is proposed that acetic acid influences phosphate absorption through its dependence on proton cotransport and that changes in J E affect the rate of phosphate absorption because of the dependence of the pmf on ΔE.