Enzymatic and non-enzymatic lipid peroxidation in leaf development

Enzymatic and non-enzymatic lipid peroxidation has been implicated in progr ammed cell death, which is a major process of leaf senescence. To test this hypothesis we developed a high-performance liquid chromatography (HPLC) me thod for a simultaneous analysis of the major hydro(pero)xy polyenoic fatty acids. Quantities of lipid peroxidation products in leaves of different st ages of development including natural senescence indicated a strong increas e in the level of oxygenated polyenoic fatty acids (PUFAs) during the late stages of leaf senescence. Comprehensive structural elucidation of the oxyg enation products by means of HPLC, gas chromatography/mass spectrometry and H-1 nuclear magnetic resonance suggested a nonenzymatic origin. However, i n some cases a small share of specifically oxidized PUFAs was identified su ggesting involvement of lipid peroxidizing enzymes. To inspect the possible role of enzymatic lipid peroxidation in leaf senescence, we analyzed the a bundance of lipoxygenases (LOXs) in rosette leaves of Arabidopsis. LOXs and their product (9Z,11E,13S,15Z)-13-hydroperoxy-9,11,15-octadecatrienoic aci d were exclusively detected in young green leaves. In contrast, in senescin g leaves the specific LOX products were overlaid by large amounts of stereo -random lipid peroxidation products originating from non-enzymatic oxidatio n. These data indicate a limited contribution of LOXs to total lipid peroxi dation, and a dominant role of non-enzymatic lipid peroxidation in late sta ges of leaf development. (C) 2001 Elsevier Science B.V. All rights reserved .