The Role of Cu in Respiration of Pea Plants and Heterotrophically Growing Scenedesmus Cells

Abstract

In Scenedesmus about half of NADH oxidation proceeds via a cyanide-sensitive and the other half via a cyanide-insensitive respiratory pathway. In contrast, respiration is completely cyanide sensitive in pea indicating that the alternative respiratory pathway is absent. Cu deficiency in pea plants and in heterotrophically grown Scenedesmus cells interferes with respiratory activity of mitochondria. In both organisms, the cyanide-sensitive NADH oxidation was strongly decreased during cultivation in low Cu media. Cu sensitivity was also observed for the alternative respiratory pathway in Scenedesmus. These results suggest that a Cu-containing component is involved in the alternative respiratory pathway. This is the main reason why alternative respiration cannot be regarded as a compensation for low cytochrome-oxidase activities during Cu starvation. The Cu dependency of the cyanide-sensitive respiration was located at the site of cytochrome oxidase. A strong coordination of the biosynthesis of the Cu-containing cytochrome-oxidase complex was evident. When the endogenous Cu pool was low, formation of cytochrome aa3, another component of cytochrome oxidase, was also decreased.