Inactivation of the respiratory chain in plant mitochondria by visible light: the primary target for photodamage and endogenous photosensitizing chromophores

Abstract

Among the respiratory complexes in plant mitochondria, ubiquinol-cytochrome c reductase (complex III) showed the highest in situ susceptibility to photoinactivation; in contrast, succinate dehydrogenase and reduced nicotinamide adenine dinucleotide dehydrogenase, which are photosensitive when present in mammalian mitochondria, were found to be fairly resistant to light. We also observed that the more sensitive the complexes are to light, the more vulnerable they are to photoensitization via the singlet oxygen ( 1O 2) mechanism. The spectral dependence of inactivation of complex III bore a close resemblance to the action spectrum for 1O 2 generation from mitochondrial membranes as well as to the absorption spectra of mitochondrial FeS centres. Histidine suppressed photoinactivation of complex III, whereas D 2O enhanced it. Destruction of the FeS centres by the treatment of mitochondria with mersalyl acid resulted in a drastic decrease in photosensitivity of the complex. These results suggests that photodamage to mitochondrial electron transport in plants results primarily from photo-oxidative inactivation of complex III by 1O 2 which is photoproduced largely by the FeS centres.