Responses ofCommelina communisL. Guard Cell Protoplasts to Abscisic Acid

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Abstract
Fitzsimons, P. J. and Weyers, J. D. B. 1987. Responses of Commelina communis L. guard cell protoplasts to abscisic acid.—J. exp. Bot. 38: 992–1001. Guard cell protoplasts (GCPs) isolated from the leaf epidermis of Commelina communis L. responded to abscisic acid (ABA) in a manner which was qualitatively and quantitatively similar to that of intact stomata. ABA inhibited swelling of GCPs under low-CO2 conditions and swollen GCPs responded to the hormone by shrinking. Both the absolute volume decrease and the initial rate of shrinking were commensurate with the extent and rates of solute loss computed for ABA-treated intact, open stomata. This indicates that GCPs represent a suitable experimental system for studies of ABA-mediated solute fluxes. A radiotracer equilibration method was developed for the rapid estimation of GCP osmotic volume changes. Using this technique it was found that, on average, 82% of the reduction in solute content caused by ABA treatment was due to the loss of K+. It is envisaged that electroneutrality might be maintained during ABA-induced shrinkage of GCPs by net inward proton movement leading to acidification of the vacuole.