Fluxes of (86)Rb (+) in "isolated" guard cells of Vicia faba L.

Steady-state (86)Rb(+) fluxes and contents were measured in stomatal guard cells of Vicia faba L., using "isolated" epidermal strips in which all cells other than the guard cells had been killed by a brief ultrasound treatment. Flux experiments were carried out for a range of stomatal apertures, achieved by incubation in light or dark, or on solutions containing different concentrations of RbCl (1-30 mM). At pH 5.5 the efflux curve of (86)Rb(+) could be fitted to the sum of two exponential terms and it was possible to calculate compartmental contents and fluxes. The data indicate that steady-state stomatal opening is achieved by regulation of both influx and efflux. Salt accumulation was not always adequate to contribute the observed osmotic requirement for opening, and this may indicate that some other solute accounts for the discrepancy.