Detoxification of SO2 derivatives in chloroplasts ofHardwickia binata

Intact chloroplasts isolated from sulphur dioxide fumigatedHardwickia binata leaves showed inhibition of PS II electron transport activity without any significant effect on photosystem I. Sulphur dioxide exposed leaves accumulated more hydrogen peroxide than those from non-fumigated plants and this was caused by increase in superoxide radical production. Hydrogen peroxide formation was inhibited by addition of cytochrome C and superoxide disrnutase. In sulphur dioxide fumigated leaves, increase in superoxide dismutase activity showed resistance to sulphite toxicity. The localization of ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase activities in chloroplasts provide evidence for the photogeneration of ascorbate. The scavenging of hydrogen peroxide in chloroplast due to ascorbate regenerated from DHA by the system: PS I → Fd → NADP → glutathione. The system can be considered as a means for preliminary detoxification of sulphur dioxide by chloroplasts