Nitrate reductase and molybdenum cofactor in annual ryegrass as affected by salinity and nitrogen source

Abstract

The influence of salinity on the activity of nitrate reductase (NR, EC 1.6.6.1) and the level of the molybdenum cofactor (MoCo) as affected by the source and concentration of nitrogen was studied in annual ryegrass (Lolium multiflorum cv. Westerwoldicum). Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS m−1, containing nitrogen (0.5 or 4.5 mM) in the form of NH4NO3 or NaNO3 Salinity‐treated (11.2 dS m−1) plants produced less biomass and more organic nitrogen while accumulating more NO−3 than control plants. Increased nitrogen concentration in the irrigation solutions enhanced biomass and organic nitrogen production as well as NO−3 accumulation irrespective of the electrical conductivity. Salinity inhibited shoot growth and increased shoot NR activity of plants receiving 4.5 mM NH4NO3 or NaNO3. Similar effects were observed in roots of plants grown in 4.5 mM NaNO3. Nitrate added to a complementation medium containing ryegrass MoCo and the NR apoprotein of Neurospora crassa mutant nit‐1 stimulated the activity of the reconstituted NR (NADPH‐nitrate reductase, EC 1.6.6.3). Increased salinity and nitrogen in the nutrient solutions caused an increase of MoCo content in roots and shoots. Similar results were observed for NR activity in the shoots. The increase of MoCo in response to salinity was more pronounced than that of NR, especially in the roots. We conclude that the pool size of MoCo in ryegrass is not constant, but varies in response to nutritional and environmental factors.

Growth Properties and Ion Distribution in Different Tissues of Bread Wheat Genotypes (Triticum aestivum L.) Differing in Salt Tolerance

“…1986). Our results supported the findings that salinity reduced shoot growth more than root growth and moderate salinity increases root biomass (Sagi et al. 1997, Kurth et al.…”

Effects of salinity on flowering, morphology, biomass accumulation and leaf metabolites in an edible halophyte

“…Halophytes are equipped with well-defined adaptive mechanisms that enable them not only to withstand periodical high salinity, but also to complete their entire lifecycles at high salinities (Flowers et al 2010). The tolerance of halophytes to salinity relies mainly on the controlled uptake of ions and the vacuolar compartmentalization of Na + , K + and Cl − with the achievement of an osmotic balance between vacuoles and cytoplasm by synthesis of osmotically active metabolites (Sagi et al 1997; Flowers and Colmer 2008). Conversely, the increased synthesis of these organic compounds and the active transport of toxic ions across the vacuolar membrane have a considerable energetic cost, resulting in growth retardation and ultimately in the reduction of productivity (Greenway and Munns 1980; Zhu 2001).…”

Pre-mature senescence in the oldest leaves of low nitrate-grown Atxdh1 mutant uncovers a role for purine catabolism in plant nitrogen metabolism

“…The catalytic center of NR and XDH1, plant 435 molybdoenzymes, requires Moco. Preferential allocation of Moco to NR supports nitrate assimilation in 436 the presence of high nitrate over AtXDH1 activity (Sagi et al, 1997. While 437 not examined here directly, the enhanced AtXDH1 activity and decreased NR activity in old leaves and 438 vice versa in young leaves, as well as the enhanced AtXDH1 activity and decreased NR activity in nitrate 439 starved plants and vice versa in leaves of high nitrate supplied plants, supports this notion (Fig.…”

“…For nitrate reductase activity the samples were extracted in a buffer containing 3 mM EDTA, 3.6 mM 517 dithiothreitol (DTT), 0.25 M Tris-HCl (pH 8.48), 3 mg L-Cys, 3 mM NaMoO4 and protease inhibitors 518 including aprotenin (10μg ml -1 ) and pepstatin (10μg ml -1 ) and the activity was detected as previously 519 described (Sagi et al, 1997). 520…”