LIGHT-INDUCED MEMBRANE-POTENTIAL CHANGES OF EPIDERMAL AND MESOPHYLL-CELLS IN GROWING LEAVES OF PISUM-SATIVUM

Light transiently depolarizes the membrane of growing leaf cells. The ionic basis for changes in cell membrane electrical potentials in response to light has been determined separately for growing epidermal and mesophyll cells of the argenteum mutant of pea (Pisum sativum L.). In mesophyll cells light induces a large, transient depolarization that depends on the external Cl- concentration, is unaffected by changes in the external Ca2+ or K+ concentration, is stimulated by K+-channel blockers tetraethylammonium (TEA(+)) and Ba2+, and is inhibited by 3-(3'-4'-dichlorophenyl)-1,1-dimethylurea (DCMU). In isolated epidermal tissue, light induces a small, transient depolarization followed by a hyperpolarization of the membrane potential. The depolarization is enhanced by increasing the external Ca2+ concentration and by addition of Ba2+, and is not sensitive to DCMU. Epidermal cells in contact with mesophyll display a depolarization resembling the response of the underlying mesophyll cells. The light-induced depolarization in mesophyll cells seems to be mediated by an increased efflux of Cl- while the membrane-potential changes in epidermal strips reflect changes in the fluxes of Ca2+ and in the activity of the proton-pumping ATPase.