When isobutyric acid (IBA) or abscisic acid (ABA) are supplied to leaf sections a similar rapid and marked decrease in the intracellular pH is observed. This acidification is accompanied by an increase in proline level which is about the same for both 3 mol m−3 IBA and 1 mol m−3 ABA treatments. Fusicoccin (FC), known to act at the proton pump level, almost completely suppresses the ABA‐induced acidification of the cell sap, whereas it only partially counteracts the acidifying effect of IBA, in particular during short periods of treatment. This effect of FC is paralleled by a similar inhibition of the induced proline accumulation: in fact, FC completely suppresses the ABA‐induced increase in proline during short treatment periods, whereas it is only effective in inhibiting the IBA‐induced proline accumulation after long treatment periods. These data seem to suggest that the ABA‐ and IBA‐induced changes in proline level might be mediated by changes in the intracellular pH.
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Pesci et al. (1985) studied this question.