Role of Inorganic Nitrogen in Synthesis and Degradation of Protein in Maize Leaves

Supply of inorganic nitrogen in the form of nitrate, ammonium and ammonium nitrate during seedling growth, increased dry weight, protein and organic nitrogen contents of the maize primary leaves. The increase in protein was more apparent during the senescent phase of the leaf. When the leaf segments from dark grown seedlings were incubated in a nutrient solution containing no nitrogen for 24 h in light, protein inorganic nitrogen contents declined appreciably. The decline was prevented by tungstate in the absence of inorganic nitrogen and the levels increased further in the presence of NH₄ Cl and NH₄, NO₃. Methionine sulfoximine also prevented this decline in the absence of inorganic nitrogen as well as in the presence of KNO₂ and NH₄ Cl. The decline in protein content of intact leaves of relatively mature seedlings was checked by inorganic nitrogen supply. Generally, the supply of tungstate or methionine sulfoximine in light or keeping the seedlings in dark, did not abolish the protective effect of inorganic nitrogen on protein. It is suggested that inorganic nitrogen prevents protein degradation in mature leaves.