Correlation between proton extrusion and stimulation of cell enlargement effects of fusicoccin and of cytokinins on leaf fragments and isolated cotyledons

Abstract

Fusicoccin (FC), a diterpene glucoside which stimulates growth of pea internode segments and of leaf fragments, is shown to induce in isolated cotyledons from germinating squash and radish seeds, an effect on cell enlargement markedly greater than that of benzyladenine (BA) and kinetin. The stimulation of cell enlargement induced in leaf fragments by FC, and in cotyledons by FC or by the cytokinins, is accompanied by a proportional rapid decrease in the pH of the medium, similar to the one previously observed when the pea internode segments are treated with auxin or with FC. This apparent proton extrusion accompanying growth stimulation by auxins, cytokinins and FC, is markedly reduced by the phosphorylation uncouplers carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP) and by the protein synthesis inhibitors cycloheximide (CH) and puromycin (PUR). A comparison of these results with those of a parallel investigation shows that the effects of growth stimulators and of the inhibitors on cell enlargement and on proton extrusion are accompanied by corresponding changes in the negative transmembrane electric potential. A model is proposed for the interpretation of the interrelationship between these effects.