Uptake of glycine by excised pulvini of Mimosa pudica in relation to proton pump activity

Abstract

Uptake of [3H]‐glycine by sections of Mimosa pudica L. pulvini is pH dependent (maximum at pH 5.5) and exhibits biphasic saturation kinetics in the range of concentrations tested (1–75 mM). Effects of compounds which increase [fusicoccin (FC)] or decrease (uncouplers, ATPase inhibitors) the proton‐motive force were tested both on the pH variations induced in the incubation medium and on glycine uptake by the pulvinar tissues: there is a close relationship between the time required for the effect of these compounds on the acidification (for FC) and the pH rise (for the inhibitors) of the medium and that needed respectively for promotion and inhibition of glycine uptake. Experiments with sulfhydryl‐reacting compounds show that N‐ethylmaleimide induces a large rise in pH in the incubation medium and strongly inhibits glycine uptake, whereas p‐chloromercuribenzenesulfonic acid has less effect on these processes. These results argue for a proton‐glycine symport mechanism in the pulvinar tissue and thus support the previously postulated involvement of a proton pump in the regulation of pulvinar movement.