Induced changes in permeability of plant cell membranes to water

The half-time for THO equilibration was three times longer for a living carrot (Daucus carota L.) cylinder than for a dead one. Furthermore, the energy of activation of THO flux was more than twice as high for the living cylinder. Passage through living membranes thus constitutes a rate-limiting step for THO flux in carrot tissue.CO(2) increased the half-time (t((1/2))) for THO equilibration. Treatment with abscisic acid or with tertiary butanol decreased t((1/2)). In neither case was the selective permeability of the membrane destroyed.p-Chloromercuribenzoate and carbonyl cyanide m-chlorophenylhydrazone, if supplied together with abscisic acid or tertiary butanol, abolished their action. If abscisic acid or butanol was first allowed to act alone, its effect was stable to subsequent treatment with the inhibitors. p-Chloromercuribenzoate and carbonyl cyanide m-chlorophenylhydrazone at concentrations at which they affected abscisic acid and butanol action, did not influence THO flux in control tissue. At considerably higher concentrations, however, 2, 4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone raised t((1/2)). The CO(2) effect was very rapidly reversible. Full reversal of the butanol effect required 3 hours, and that of abscisic acid required 4 days.