Free radical metabolism, pigment degradation and lipid peroxidation in leaves during senescence

Abstract

Synopsis Various lines of evidence suggest that the controlled increase in the production of oxygen radicals is an important factor involved in phytohormone metabolism, selective changes in membrane permeability, degradation of photosynthetic pigments and unsaturated membrane lipids, oxidative modification and subsequent proteolytic degradation, and other events occurring in ageing and senescing leaves. Increased lipid peroxidation, appearance of chlorophyll allomerised products, as well as fluorescent ‘lipofuscin-like’ pigments have been documented in different systems of leaf senescence. On the other hand, the accumulation of peroxidised products may result from the alteration to native structural organisation and energy dissipation reactions of the photosynthetic apparatus. Although there are contradictory and incomplete data on the activity of the systems involved in the metabolism of oxygen radicals, it seems that senescing leaves retain, at least in part, their defence potential against both activated oxygen species and toxic lipid peroxidation products. This provides the plant with the ability to successfully dismantle its photosynthetic apparatus during senescence in a relatively safe manner.