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Short‐term nitrogen‐induced modulation of phospho enol pyruvate carboxylase in tobacco and maize leaves
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Edité par CCSD ; Oxford University Press (OUP) -
International audience. Untransformed maize and tobacco plants and tobacco plants constitutively expressing nitrate reductase were grown with sufficient NO−3 to support maximal growth. Four days prior to treatment the tobacco plants were deprived of nitrogen. Excised maize leaves and tobacco leaf discs were fed with either 40 mM KNO 3 or 40 mM KCl (control) in the light. Phospho enol pyruvate (PEP) carboxylase (Case) activity was measured at 0.3 mM and 3 mM PEP. The light‐ induced increase in PEPCase Vmax was greater in maize than tobacco. Furthermore light decreased malate sensitivity in maize (which was N‐replete) but not in N‐deficient tobacco. NO−3 treatment increased PEPCase Vmax values in both species and decreased the sensitivity to inhibition by malate, but effects of NO−3 were much more pronounced in tobacco than maize. PEPCase kinase activity was, however, greater in maize leaves fed NO−3 than in the Cl − ‐treated controls, suggesting that it is responsive to leaf nitrogen supply. A correlation between foliar glutamine content and PEPCase activity was observed. It is concluded that PEPCase is sensitive to N metabolites which favour increased flow through the anapleurotic pathway in both C 3 and C 4 plants.
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