Short-term nitrogen-induced modulation of phosphoenolpyruvate carboxylase in tobacco and maize leaves
Murchie, E.H. | Ferrario-Mery, S. | Valadier, M.H. | Foyer, C.H.
Untransformed maize and tobacco plants and tobacco plants constitutively expressing nitrate reductase were grown with sufficient NO3(-) 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 KNO3 or 40 mM KCl (control) in the light. Phosphoenolpyruvate (PEP) carboxylase (Case) activity was measured at 0.3 mM and 3 mM PEP. The light-induced increase in PEPCase V(max) was greater in maize than tobacco. Furthermore light decreased malate sensitivity in maize (which was N-replete) but not in N-deficient tobacco. NO3(-) treatment increased PEPCase V(max) values in both species and decreased the sensitivity to inhibition by malate, but effects of NO3(-) were much more pronounced in tobacco than maize. PEPCase kinase activity was, however, greater in maize leaves fed NO3(-) 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 C3 and C4 plants.
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