Some effects of light on the interconversion of metabolites in green leaves

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Abstract
Evidence is presented that the Krebs cycle occurs in green leaves in the light as well as in the dark. When leaves are fed with various labelled metabolites (including glutamate, asparate, the major Krebs-cycle intermediates and CO2) the ratio labelled malate/labelled asparate is high in the light and low in the dark. When leaves are fed with labelled oxaloacetate more of this intermediate is reduced to malate in the light than in the dark. A high ratio of labelled malate/labelled asparate can be induced in mitochondira by exposure to reducing conditions but not by inhibition of pyruvate oxidation. These findings provide an alternative explanation to the postulated light-inhibition of pyruvate oxidation in green plants.