Correlation between cell enlargement in pea internode segments and decrease in the pH of the medium of incubation: II. Effects of inhibitors of respiration, oxidative phosphorylation and protein synthesis

Abstract

Inhibitors of respiration (CO), oxidative phosphorylation (2,4-dinitrophenol [DNP] and carbonyl cyanide m-chlorophenyl-hydrazone [CCCP]), RNA (actinomycin D [Act D]) and protein synthesis (cycloheximide [CHI] also inhibit, in the excised pea internode test, both auxin- or fusicoccin-stimulated cell enlargement and the progressive decrease of pH in the incubation medium. The inhibition of the “pH effect” is not due to an inhibitor-induced extrusion of buffering substances from the tissues. In the segments prepared from the growing part of the distal internode the markedly greater effect of fusicoccin (FC), as compared to indole-3-acetic acid (IAA), on growth stimulation and on the pH decrease is accompanied by a correspondingly greater increase of respiration. In segments from fully grown internodes, IAA has almost no effect on growth, respiration, and lowering of the pH in the medium, while FC still stimulates respiration and induces the pH decrease effect. These data are interpreted as further support for the hypothesis that the effect of growth-promoting substances on cell enlargement is mediated by their capacity to induce a metabolism-dependent change of H + concentration at the level of the cell wall.