| Abstract: | Fitzsimons, P. J. and Weyers, J. D. B. 1987. Responses of Commelinacommunis L. guard cell protoplasts to abscisic acid.—J.exp. Bot. 38: 992–1001. Guard cell protoplasts (GCPs) isolated from the leaf epidermisof Commelina communis L. responded to abscisic acid (ABA) ina manner which was qualitatively and quantitatively similarto that of intact stomata. ABA inhibited swelling of GCPs underlow-CO2 conditions and swollen GCPs responded to the hormoneby shrinking. Both the absolute volume decrease and the initialrate of shrinking were commensurate with the extent and ratesof solute loss computed for ABA-treated intact, open stomata.This indicates that GCPs represent a suitable experimental systemfor studies of ABA-mediated solute fluxes. A radiotracer equilibrationmethod was developed for the rapid estimation of GCP osmoticvolume changes. Using this technique it was found that, on average,82% of the reduction in solute content caused by ABA treatmentwas due to the loss of K+. It is envisaged that electroneutralitymight be maintained during ABA-induced shrinkage of GCPs bynet inward proton movement leading to acidification of the vacuole. Key words: Abscisic acid, Commelina communis L., guard cells, protoplasts |
