Abstract

Abstract 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 sub­ chloroplast 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 photo­ system I or activated after its destruction.

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