Active oxygen participation in chlorophyll destruction and lipid peroxidation in SO2-fumigated leaves of spinach

摘要

Chlorophyllaand carotenoids of spinach began to be destroyed 2 to 3 hr after fumigation with 2 ppm SO2under light, whereas chlorophyllbwas undamaged during 8 hr of exposure to SO2. Pheophytinawas not affected by the fumigation.When disks excised from leaves fumigated with SO2at 2 ppm for 2 hr were illuminated, chlorophyllaand carotenoids were broken down, while they were not destroyed in darkness. The destruction of these pigments was suppressed under nitrogen. Chlorophylladestruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate (tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-2,2,2-octane (DABCO), methio-nine, histidine, benzoate and formate. Chlorophylladestruction was inhibited by phenazine methosulfate but stimulated by methyl viologen. Addition of superoxide dismutase (SOD) to the homogenate of SO2-fumigated leaves inhibited the chlorophylladestruction. The activity of endogenous SOD was reduced to 40by 2-hr fumigation before the loss of chlorophyll was observed. These results suggest that chlorophylladestruction by SO2was due to superoxide radicals (O2−).Moreover, malondialdehyde (MDA), a product of lipid peroxidation, was formed in SO2-fumigated leaves. MDA formation was inhibited by tiron, hydroquinone and DABCO but not by benzoate and formate. MDA formation was increased by D2O. These results suggest that lipid peroxidation in SO2-fumigated leaves was due to singlet oxygen1O2produced from O2