Effects of Ultraviolet Radiation on the Plasma Membranes of Chara corallina. II* The Action Potential

Abstract

When cells of C. corallina were irradiated with 254 nm ultraviolet light, the action potential across the plasmalemma was unaffected in its peak height, but its duration (measured at half-peak height) was increased, more so as the dose was varied between 1500 and 6000 J m-². The action potential across the tonoplast was reduced in peak height and increased in duration by U.V. The effects were slowly reversible. The effect of 285 nm u.v., effective in depolarizing the resting potential difference, was to decrease the peak of the plasmalemma action potential while leaving the duration virtually unaffected. The results are interpreted as revealing differential effects on gating mechanisms determining the duration, and on transient membrane permeability to chloride (and possibly potassium) determining the peak, of the action potential. Because of the differential wavelength effects, these two membrane properties are postulated to be mediated by molecules which act as distinctive targets to the two wavelengths.