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Metabolism of glycolic acid-1- 14 C in barley leaves with or without added CO 2

1971; Canadian Science Publishing; Volume: 49; Issue: 2 Linguagem: Inglês

10.1139/b71-049

1480-3305

Imre A. Tamàs, R. G. S. Bidwell,

Microbial Community Ecology and Physiology

Detached primary leaves of barley (Hordeum vulgare L. var. Dayton) were supplied with glycolate-1 - 14 C in light or darkness with or without CO 2 , and the radioactivity of soluble metabolites and evolved CO 2 was measured at intervals. The results of these experiments suggest that exogenously supplied glycolate is metabolized by two distinct pathways in illuminated leaves. It may be converted to sucrose outside the chloroplasts, presumably via the glycolate pathway. Alternatively glycolate carbon, through some product of its metabolism, enters the chloroplasts and becomes incorporated into intermediates of the Calvin cycle, from which photorespired CO 2 is derived. Endogenous glycolate, originating from Calvin cycle intermediates, may leave the chloroplasts and become a substrate for sucrose synthesis. Exchange of carbon therefore appears to take place between the Calvin cycle inside and the glycolate pathway outside the chloroplasts. This exchange gives a net flow of carbon out of the chloroplasts during photosynthetic CO 2 fixation. However, at low external CO 2 concentration the flow of carbon from the glycolate pathway into the Calvin cycle in chloroplasts is greatly enhanced, providing substrate for CO 2 production. Exogenous glycolate apparently does not directly enter the site of CO 2 production in light. However, it is converted to CO 2 in darkness, without the participation of the Calvin cycle.