Nitrogen Metabolism of Soybeans

Abstract

The effects of N source (6 mm nitrogen as NOs-or urea) and tungstate (0, 100, 200, 300, and 400 FM Na2WO4) on nitrate metabolism, nodulation, and growth of soybean (Glycine max IL.1 Menf.) plants were evaluated.Nitrate reductase activty and, to a lesser extent, N03-content of leaf tissue decreased with the addition of tungtate to the nutrient growth medium. Concomitantly, nodule mass and acetylene reduction activity of NO3-grown plants Increased with addition of tungstate to the nutrient solution. In contrast, nodule mass and acetylene reduction activity of ureagrown plants decreased with increased nutrient tungstate levels. The acetylene reductin actvity of nodulated roots of NOs--grown plants was less than 10% of the activity of nodulated roots of urea-grown plants when no tungstate was added. At 300 and 400 pM tungstate levels, acetylene reduction actity of nodulated roots of NO3-grown plants exceeded the activity of comprable urea-grown plants.Addition of tungstate to the nutrient solution decreased plant growth, regardless of the N source, although the effect was more pronounced with NOs-nutrition. The Increased nodulation and decreased nitrate reductase activity noted with plants grown In the presence of tungstate and a high (6 mM) external supply of NO. suggests that N03-does not directly inhibit nodulatin but rather affects nodulation indirectly through subsequent metabolism of NO5.The inhibitory effect of NO3 on nodulation of soybean is well documented (2). Munns (6) and Trifolium subterraneum L., respectively) any better than did parent strains with nitrate reductase activity. They concluded that it was unlikely that reduction of N03-to N02 by the rhizobia played a significant role in the inhibition of nodulation by NO3-. The more marked inhibitory effect of NO3 than of urea on soybean nodulation (4) also suggested a more direct effect of N03-on nodulation. However, urea was taken up more slowly than N03 (12), and the more marked inhibition by N03 may still involve a less favorable C:N ratio. Therefore, the mechanism of inhibition of nodulation by combined N is not clear.The known inhibitory effect of tungstate on nitrate reductase activity in higher plants (5,8,10) suggested that the addition of tungstate may be a means of separating the direct and indirect effects of N03 on nodulation. The inhibition of nitrate reductase by tungstate results from the formation of a tungstate protein analog lacking nitrate reductase activity (8). Rao and Rains (10) showed that tungstate had no effect on N03 uptake in short term (3 hr) studies with barley, although it completely inhibited nitrate reductase activity.Data concerning effects of tungstate on nodulated legumes are limited. Quin and Hoglund (9) reported that 5 ,ug/g tungstate in nutrient solution slightly depressed growth and N accumulation of white clover (Trifolium repens L.) which was solely dependent on atmospheric N2 as the N source. In a field study with white clover, Davies and Stockdili (1) showed that addition of tungstate without molybdat...

The exudate from an arbuscular mycorrhizal fungus induces nitric oxide accumulation in Medicago truncatula roots

“…To further test whether NR is involved in exudate-induced NO production, DAF-2T fluorescence was measured in roots where NR activity was inhibited by treatment with tungstate (Harper and Nicholas 1978;del Giudice et al 2011) prior to fungal exudate application. The plots presented in Fig.…”

Nitrate Reductases from Wild-Type and nr1-Mutant Soybean (Glycine max [L.] Merr.) Leaves

“…The cNR and iNR activities were shown to be under different genetic control and therefore isozymes (for review, see Harper et al [14]). Tungstate, an analog of molybdate, was shown to inhibit iNR but not cNR activity (2,13,18). This finding caused Aslam (2) to suggest that Mo may not be required for cNR activity.…”

Nitric Oxide in Azospirillum and Related Bacteria: Production and Effects

“…Tungstate can compete with molybdate for incorporation into the enzyme complex and results in the inactivation of molybdate-dependent enzymes (Harper and Nicholas 1978 ;Hille 2002 ). Tungstate is widely used as a NR inhibitor in plant NO research (Mendel 2007 ) and also in bacteria culture (Betlach and Tiedje 1981 ).…”