Light-triggered action potentials in plants

Abstract

Special attention is paid in this paper to the criteria of the light-triggered action potential, namely the all-or-none law, propagation, the occurrence of refractory periods. Such action potentials have been recorded in Acetabularia mediterranea, Asplenium trichomanes, Bryum pseudotriquetrum, Eremosphaera viridis and Concephalum conicum. In Acetabularia, action potentials are generated after sudden cessation of light stimuli of sufficient intensity. The depolarization phase of the action potential develops as a result of a transient reversal of the action of the electrogenic Cl- pump. This is a principle of the "metabolic" action potential hypothesis proposed by Gradmann. In the gametophytes of Aspleniam trichoma­nes and Bryum pseudo triquetrum, action potentials are triggered on illumination. Gutation starts 1.5-2 seconds after the passage of an action potential. The active water secretion facilitates fertilization. In the unicellular fresh water alga, Eremosphaera viridis, action potential-like responses are evoked after light termination. The process responsible for its appearance is the opening of potassium channels in the plasmalemma. The liverwort, Conocephalum conicum, generates action potentials in response to light, electrical, chemical and mechanical stimuli. Calcium and potassium channels as well as proton pumps are involved in electrogenesis of action impulses in the species. Excitation causes a significant increase in the respiration rate. The role of action impluses as mediators in a system of a metabolism control is discussed.