The interaction of senescence and wounding in oat leaves. II. Chlorophyll breakdown caused by wounding in light

Abstract

The influence of wounding on the senescence of oat ( Avena sativa L.) leaf segments held in continuous white light was studied. It was noticed that leaf segments held in white light, which in general delays senescence, actually showed increased loss of chlorophyll within a few millimeters of the cut ends. When the whole segment was subjected to different types of wounding, chlorophyll loss was promoted in all cases and the loss increased with increase in the intensity of wounding. While 50% of the initial chlorophyll content was retained in the control segments after 6 days, wounding reduced that figure to as little as 24%. The increase in chlorophyll loss was already measurable by the second day. The presence of calcium and magnesium promoted the loss of chlorophyll (Chl). The action of wounding on proteolysis, however, was the opposite, for wounding synergized the effect of light in delaying proteolysis. A number of previously reported senescence-modifying substances were tested and even in presence of these substances wounding still promoted chlorophyll loss. However, these compounds differed in their effect on the protein content, some promoting proteolysis and others inhibiting it. Chl loss was not antagonized by reducing agents. The effect of wounding in light was reversed as soon as the segments were transferred from the light to darkness. Possible mechanisms for these peculiar effects are discussed.