Nitrogen Fixation of Nodulation Mutants of Soybean as Affected by Nitrate

Abstract

It was previously reported that three soybean (Glycine max [L.] Merr.) nodulation mutants (NOD1-3, NOD2-4, and NOD3-7) were partially tolerant to nitrate when nitrate was supplied simultaneously with inoculation at the time of transplanting. The current study evaluated the effect of short-term nitrate treatment on nitrogenase activity (C2H2 reduction per plant and per nodule weight) and on relative abundance of ureides when nitrate application was delayed until plants were 3 weeks old and nodules were fully developed. Nitrogenase activity of the mutants was similar to that of Williams after an initial 3-week growth period, prior to nitrate treatment. Application of 5 millimolar nitrate resulted in greater inhibition of nitrogenase activity in Williams than in the three mutants. NOD1-3 was most tolerant of nitrate among the mutants tested and showed the highest relative abundance of ureides. Although C2H2 reduction activity per plant for NOD1-3 was higher than for Williams in the presence of nitrate, C2H2 reduction activity per gram of nodules was lower for NOD1-3 than for Williams in the presence and absence of nitrate. Compared to Williams, NOD1-3 had higher nodule ureide concentration and had similar glutamine synthetase activity in nodule tissue, indicating its nodules have normal nitrogen assimilation pathways. Nitrate application resulted in ureide accumulation in nodule tissue as well as in all plant parts assayed. Unexpectedly, nitrate treatment also increased the rate of ureide degradative capacity of leaves in both NOD1-3 and Williams. The data confirmed that nitrogenase activity of the selected nodulation mutants was more, but still only partially, tolerant of nitrate compared with the Williams parent.also had higher ureide concentration in its nodule tissue (13), likely due to limited growth of the mutant which may have impaired ureide utilization.Partially nitrate tolerant mutants of soybean (NOD1-3, NOD2-4, and NOD3-7) have also been selected from mutagenized Williams populations, and initial characterization of these mutants has been reported (4). The data indicated many similar characteristics of our mutants to those reported by Carroll et al. (1, 2). However, it is not known whether the nitrogenase activity of our mutants is tolerant to nitrate per se, since in the previous study (4) the effects of nitrate on infection steps and on subsequent nodule function could not be separated due to simultaneous inoculation and nitrate addition. Using "5N analysis it was determined that NOD 1-3 fixed more '5N2 than Williams, when grown on urea, and that all three nodulation mutants symbiotically fixed more N2 than wild type when the mutants were grown on nitrate (1 1). This confirmed the earlier report based on C2H2 reduction assays (4). In the present report, nitrate treatment was delayed until plant roots were well nodulated and capable of relatively high N2 fixation activity. N2 fixation was then assessed by using the in situ C2H2 reduction assay and determining the relative abundance of ureide...

Photoassimilate partitioning in hypernodulation mutant of soybean (Glycine max(L.) Merr.) NOD1-3 and its parent williams in relation to nitrate inhibition of nodule growth

“…3A, B). These results are also consistent with the findings reported in previous studies (Wu and Harper 1990). However, the response of ARA to nitrate cannot be simply explained by the higher nodule mass or number.…”

“…It was reported that the total nodule mass (dry weight) of NODl-3 was significantly higher than that of the parent even at a high level of nitrate supply (Gremaud and Harper 1989;Wu and Harper 1990). The results of the present study which included nitrate treatment (5 mM), contributed to new information indicating that the individual nodule growth estimated by the increase in the nodule diameter was also partially nitrate-tolerant in NODI-3 (Fig.…”

“…In spite of these outstanding traits for N acquisition, the values for the plant growth and seed yield of the mutant lines were lower than those of the parent lines in field experiments, irrespective of nitrogen conditions (Wu and Harper 1991;Suganuma et al 2001). Furthermore, ARA (on a g dry weight basis) of the nodules was lower for NOD 1-3 than for Williams, regardless of the presence or absence of nitrate, although ARA per plant for the mutant was higher than that of the parent lines (Wu and Harper 1990). It is also well known that the nodule size of the mutant lines is smaller than that of the parent lines, although the mutant displays a more profuse nodulation than the parents (Sato et al 1999).…”

“…Bragg were reported to be nitrate-tolerant and designated as nts (nitrate-tolerant symbiosis) mutants (Carroll et al 1985). It was, however, subsequently shown that these mutants were still sensitive to nitrate, depending on the cultivation methods or growth stages (Eskew et al 1989;Wu and Harper 1990).…”

Shoot-root control of nitrate tolerance of N2 fixation in spontaneously tolerant soybean lines: reciprocal grafting experiments

“…In the mutant type, the shoot-derived autoregulation signal would be either altered or absent, inducing a supernodulant and nitrate-tolerant (for nodulation) phenotype. In terms of nitrogen fixation, supernodulating mutants showed a low specific activity (C 2 H 2 reduction / nodule biomass), and this activity was reduced in the presence of nitrate in the same proportion as for the wild type parent (soybean: Hansen et al, 1990;Wu and Harper, 1990;pea: Jacobsen and Feenstra, 1984;com-mon bean: Buttery and Park, 1990). This last result was not always confirmed for soybean; a lower inhibition of specific activity was observed for the mutant type (Schuller et al, 1988).…”