Paraquat-Catalyzed Photodestructions in Subchloroplast Particles are Independent on Photosynthetic Electron Transport

Light dependent ethane formation and chlorophyll bleaching in isolated chloroplast lamellae are enhanced by either methylviologen or α-linolenic acid. Both ethane formation and chlorophyll bleaching are also enhanced in chloroplast particles deficient in photosynthetic electron transport, e.g. after aging, heat treatment or digitonin fragmentation. Ethane formation by subchloroplast particles from endogenous substrates in the presence of methylviologen is inhibited by superoxide dismutase or by a penicillamine copper complex exhibiting superoxide dismutase activity whereas chlorophyll bleaching is enhanced by superoxide dismutase – active substances. Maximal rates of ethane formation in subchloroplast particles are observed when more than 50% of the chlorophyll is bleached and continues after 98% chlorophyll bleaching. This result indicated that methylviologen – stimulated ethane production in subchloroplast particles is not dependent on photosynthetic electron transport but involves “activated oxygen” – species like the superoxide radical ion, generated by a light receptor derived from the pigmentsystem of photosystem I or activated after its destruction.