Relation between leaf senescence and stomatal closure: Senescence in light

Abstract

Senescence of isolated oat [cv. victory] seedling leaves, floating on water or solutions in white light, was followed by the disappearance of chlorophyll and the liberation of free amino N. In parallel, stomatal apertures were measured with a diffusion resistance porometer and borne out also by changes in fresh weight. The stomata open in the light slowly begin to close after the first day; in the dark they close at once but gradually begin to open on successive days. Abscisic acid causes closure and this is accompanied by senescence. Phenylmercuric nitrate also causes closure and again the reaction is closely paralleled by senescence. Kinetin maintains stomatal opening even more than does light alone, and this is accompanied by complete prevention of chlorophyll loss for at least 5 days. Covering the leaf surface with a film of Vaseline, especially when detergents are added, accelerates sensecence. Floating the leaf segments on hypertonic solutions of sucrose or mannitol suffices to bring the rate of senescence in light up to the rate in darkness. Apparently the effect of light in delaying senescence is primarily due to its effect on the stomatal aperture. Stomatal aperture may be the principal controlling agent in leaf senescence.