Nitrate Reductase Activity in Wheat Seedlings as Affected by NO 3-/NH 4+ Ratio and Salinity

Abstract

Summary Nitrate reductase is considered to be a limiting factor for growth, development and protein production in plants. This enzyme is influenced by external conditions. The purpose of this study was to investigate the effect of different NO 3 -/NH 4 + ratios and salinity on NRA (nitrate reductase activity) in shoots and roots of wheat ( Triticum aestivum L. cv. Betres) seedlings. Plants were grown in a growth chamber under controlled conditions. Nutrient solution contained 4 mM N, applied as NO 3 - and NH 4 + in different ratios, and saline treatments consisted in two levels of NaCl: 1 mM and 60 mM. Wheat seedlings had most of their NRA in shoots. When NH 4 + was present in the nutrient solution NRA was almost completely inhibited in roots and decreased in shoots. Inhibition of NRA by NH4+ seems to be a direct effect on synthesis and activity of NR rather than through inhibition of NO 3 - uptake and thus by lack of substrate. Salinity significantly decreased NRA in shoots, this effect being influenced by NO 3 - in the and by NO 3 -/Cl - ratio in shoots. The effect on RNA may be due to the alteration of NO 3 - uptake, to an excessive CI - shoot content which may affect NO 3 - transport from vacuoles to cytoplasm and to the alteration of NO 3 - flux from root to shoot.