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Effects of Sulfite on Metabolism in Isolated Mesophyll Cells from Papaver somniferum ¹

Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720

Exposure (30 minutes) of leaf-free mesophyll cells from the C-3 plant, Papaver somniferum, to concentrations of sulfite (SO₂ + HSO₃^– + SO₃^–) up to 20 millimolar stimulated the rate of CO₂ incorporation as much as 30%. The sulfite rapidly affects the metabolism of newly incorporated CO₂. Ammonia incorporation into glutamine and subsequent transamination reactions were stimulated during the short term exposure periods while glycolate metabolism apparently was inhibited by bisulfite at two points in the pathway. The results further indicate that glycolate is the major precursor of glycine in these cells. Prolonged periods of exposure (24 hours) to sulfite had somewhat different effects on carbon metabolism: the high concentrations (10 to 20 millimolar) severely inhibited all aspects of cellular metabolism while lower concentrations (1 millimolar) appeared to inhibit ammonia incorporation but stimulated synthesis of sucrose and starch.