Murchie E H, Ferrario-Méry S, Valadier M H, Foyer C H
Laboratoire du Métabolisme et de la Nutrition des Plantes, INRA, Route de St Cyr, 78026 Versailles Cedex, France.
J Exp Bot. 2000 Aug;51(349):1349-56.
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. 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. NO(3)- treatment increased PEPCase V:(max) 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 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.
未转化的玉米和烟草植株以及组成型表达硝酸还原酶的烟草植株在供应充足的NO₃⁻以支持最大生长量的条件下生长。在处理前四天，对烟草植株进行缺氮处理。将离体的玉米叶片和烟草叶圆片在光照下分别用40 mM KNO₃或40 mM KCl（对照）处理。在0.3 mM和3 mM磷酸烯醇式丙酮酸（PEP）浓度下测定磷酸烯醇式丙酮酸羧化酶（PEPCase）的活性。光照诱导的PEPCase最大反应速度（Vmax）的增加在玉米中比在烟草中更大。此外，光照降低了玉米（氮充足）中苹果酸的敏感性，但在缺氮的烟草中则没有。NO₃⁻处理增加了两个物种中PEPCase的Vmax值，并降低了对苹果酸抑制的敏感性，但NO₃⁻的影响在烟草中比在玉米中更为明显。然而，玉米叶片中NO₃⁻处理组的PEPCase激酶活性高于Cl⁻处理的对照组，这表明它对叶片氮供应有反应。观察到叶片谷氨酰胺含量与PEPCase活性之间存在相关性。得出的结论是，PEPCase对N代谢产物敏感，这些代谢产物有利于增加C₃和C₄植物中回补途径的通量。
