Gram Of Nodule Research Articles

Sulfuric acid leaching of ocean manganese nodules using phenols as reducing agents

Pacific Ocean manganese nodule samples were leached with dilute sulfuric acid in the presence of phenol type aromatic reducing agents. Six phenols, including hydroxybenzene, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, o-trihydroxybenzene and m-trihydroxybenzene, were tested. The results indicated that all the tested phenols were effective reducing agents that significantly increased the extraction of Mn, Cu, Ni, Co from the nodules. At a dosage of 0.25 ∼ 0.4 grams of the reducing agents and 0.925 grams of H 2SO 4 per gram of nodules, over or nearly 95% of the Mn, Cu, Ni and Co could be extracted in 10 ∼ 20 minutes from an aqueous slurry containing about 20% manganese nodule, under ambient temperature and pressure. In the absence of the reducing agents, the extraction of Cu was about 65% and that of Mn, Ni and Co was below 20%. ESCA, TLC and UV/VIS spectroscopic analyses indicated that the Mn in the nodules was reduced in the presence of phenols in the acid medium, while the phenols could be oxidized to p-benzoquinone.

Biomass allocation and nitrogenase activity in Alnus tenuifolia: Responses to successional soil type and phosphorus availability

Low soil phosphorus availability and leachates from poplar (Populus balsamifera L.) have been hypothesized to limit growth and nitrogen fixation of thinleaf alder (Alnus tenuifolia Nutt.) in primary successional forests of the Tanana River floodplain (interior Alaska). This greenhouse study isolates the effects of P availability and soil type (successional stage) on alder seedling growth and N2 fixation (acetylene reduction). We grew seedlings in soil cores collected from early-successional alder stands and mid-successional poplar stands (poplar overstories with alder understories) which had been untreated or P fertilized in a field experiment. Total nodule biomass and nitrogenase activity per plant (measured at harvest) were similar among alders in both the alder and poplar soil. Alders grew larger in poplar soil, but nitrogenase activity per gram of nodule was higher among alders grown in alder soil. Alders in fertilized soils grew larger than controls and increased biomass allocation to nodules, resulting in much higher nitrogenase activity per plant, but nitrogenase activity per gram of nodule did not differ. Fertilization had a smaller effect on total plant biomass and total nodule biomass in alders grown in poplar soil than in alder soil. Results suggest that low soil P could limit alder growth and N2 fixation in these floodplain forests, but poplar soil is unlikely to limit growth and N2 fixation relative to alder soil at natural levels of P.

Relative growth and nodulation of tropical legume species with contrasting persistence and seedling vigor

Carpon desmodium [Desmodium heterocarpon (L.) DC] has proven to be a useful perennial pasture legume for some sites in peninsular Florida. However, slow seedling growth rates have made commercial plantings vulnerable to competition from grasses and weeds and to even short periods of drought. Other, less persistent, legumes establish more dependably in the region. Three legume species with contrasting seedling vigor and plant development were evaluated in plantings of mixtures of the three legumes and bahiagrass (Paspalum notatum Flugge). Plant development was monitored to determine if nutritional limitations associated with root development or nodulation impair establishment of carpon desmodium. Every two weeks through the growing season, six plants of each legume in each of four replications were dug to determine shoot dry weight, root dry weight, nodule number, nodule dry weight, and shoot to root ratio. Nitrogenase activity was also assayed by acetylene reduction. Shoot, root, and nodule weights and nodule number were substantially lower for carpon desmodium during early seedling development than for phasey bean [Macroptilium lathyroides (L.) Urb.] or aeschynomene (Aeschynomene americana L.). Nitrogenase activities per gram of nodule were highly variable with no differences detected among species or sampling dates. Nodules were much slower to develop on carpon desmodium than on the other two species, and this delayed nodulation is suggested to be a major limitation in development of seedlings of this species.

Enhanced Nodulation and Nitrogen Fixation by a Revertant of a Nodulation-Defective Bradyrhizobium japonicum Tryptophan Auxotroph

In greenhouse studies, the symbiotic properties of a prototrophic revertant (TA11 NOD) of a nodulation defective tryptophan auxotroph of Bradyrhizobium japonicum were compared with those of the normally nodulating wild-type strain, B. japonicum I-110 ARS. Strain I-110 ARS was the parent of auxotrophic mutant TA11. Plants inoculated with TA11 NOD contained significantly more nitrogen per plant than did plants inoculated with wild-type bacteria (275.9 +/- 35 versus 184 +/- 18 mg). Also, plants that received the revertant were larger, averaging 8.4 +/- 0.9 g (dry weight) versus 6.4 +/- 0.6 g for those that received the wild-type bacterial strain. Additionally, plants that received the NOD strain had 56% more nodules and 41% more nodule mass than did control plants. With both inocula, average nodule size and amount of nitrogen fixed per gram of nodule were about the same. These data indicated that the improvement in nitrogen fixation observed with the TA11 NOD resulted from an increase in the overall nodule number. The physiological basis for this increase in nodulation is not known, but enhanced tryptophan catabolism does not appear to be involved.

Nitrogen Fixation of Nodulation Mutants of Soybean as Affected by Nitrate

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 (C(2)H(2) 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 C(2)H(2) reduction activity per plant for NOD1-3 was higher than for Williams in the presence of nitrate, C(2)H(2) 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.

Effect of Oxygen and Malate on NO3− Inhibition of Nitrogenase in Soybean Nodules

Soybean (Glycine max cv Hodgson) nitrogenase activity (C(2)H(2) reduction) in the presence or absence of nitrate was studied at various external O(2) tensions. Nitrogenase activity increased with oxygen partial pressure up to 30 kilopascals, which appeared to be the optimum. A parallel increase in ATP/ADP ratios indicated a limitation of respiration rate by low O(2) tensions in the nodule, and the values found for adenine nucleotide ratios suggested that the nitrogenase activity was limited by the rate of ATP regeneration. In the presence of nitrate, the nitrogenase activity was low and less stimulated by increased pO(2), although the nitrite content per gram of nodules decreased from 0.05 to 0.02 micromole when pO(2) increased from 10 to 30 kilopascals. Therefore, the accumulation of nitrite inside the nodule was probably not the major cause of the inhibition. Instead, inhibition by nitrate could be due to competition for reducing power between nitrate reduction and bacteroid or mitochondrial respiration inside the nodule. This is supported by the observation of decrease in ATP/ADP ratios from 1.65, in absence of nitrate, to 0.93 in the presence of this anion at 30 kilopascals O(2). Furthermore, the inhibition was suppressed by the addition, to the plant nutrient solution, of 15 millimolar l-malate, a carbon substrate that is considered to be the major source of reductant for the bacteroids in the symbiosis.

The effects of soybean cultivar, rhizobium strain and nitrate on plant growth, nodule mass and acetylene reduction rate

The effects of twelve strains ofBradyrhizobium japonicum and ten cultivars of soybean (Glycine max (L.) Merr.) on plant and nodule weights, and acetylene reduction rates (33 to 41 days) were measured in the presence and absence of 6mM nitrate. No interactions between strains and cultivars were observed. Strain by nitrate interactions were found for plant and nodule weights, and acetylene reduction rates per gram of nodule. Cultivar by nitrate interactions were found for nodule weights, acetylene reduction rates per plant and per gram of nodule. Blackhawk with all strains, and all cultivars with strains 110 and CB 1809, seemed to be able to grow as well in the absence of nitrate (utilizing nodule fixation) as in its presence.

Influence of 5-Methyltryptophan-Resistant Bradyrhizobium japonicum on Soybean Root Nodule Indole-3-Acetic Acid Content

Bradyrhizobium japonicum mutants resistant to 5-methyltryptophan were isolated. Some of these mutants were found to accumulate indole-3-acetic acid (IAA) and tryptophan in culture. In greenhouse studies, nodules from control plants inoculated with wild-type bradyrhizobia contained 0.04, 0.10, and 0.58 mug of free, ester-linked, and peptidyl IAA g (fresh weight) of nodules, respectively. Nodules from plants inoculated with 5-methyltryptophan-resistant bradyrhizobia contained 0.94, 1.30, and 10.6 mug of free, ester-linked, and peptidyl IAA g (fresh weight) of nodules, respectively. This manyfold increase in nodule IAA content indicates that the Bradyrhizobium inoculum can have a considerable influence on the endogenous IAA level of the nodule. Further, these data imply that much of the IAA that accumulated in the high-IAA-containing nodules was of bacterial rather than plant origin. These high-IAA-producing 5-methyltryptophan-resistant bacteria were poor symbiotic nitrogen fixers. Plants inoculated with these bacteria had a lower nodule mass and fixed less nitrogen per gram of nodule than did plants inoculated with wild-type bacteria.

Host-genetic control of nitrogen fixation in the legume-Rhizobium symbiosis: complication in the genetic analysis due to maternal effects

In pea cv. Afghanistan a recessive gene sym 6 prevents the full expression of nitrogenase activity in root nodules, induced byRhizobium leguminosarum strain F 13. In contrast, nitrogenase activity is fully expressed in pea cv. Iran. A comparison of the reciprocal hybrids of these two plants showed that the size of the plant was determined by the mother plant (maternal effect). Therefore the shoot weight and the total amount of nitrogen fixed are not suitable as parameters for a genetic analysis. The % nitrogen of the shoot and the specific activity of the nodules per gram of nodules are more reliable, but for practical purposes the specific activity of the nodules expressed per gram of shoot tissue can be used.

Proteolytic Activity in Soybean Root Nodules

Root nodules were harvested from chamber-grown soybean (Glycine max L. Merrill cv Woodworth) plants throughout development. Apparent nitrogenase activity (acetylene reduction) peaked before seeds began to develop, but a significant amount of activity remained as the seeds matured. Nodule senescence was defined as the period in which residual nitrogenase activity was lost. During this time, soluble protein and leghemoglobin levels in the host cell cytosol decreased, and proteolytic activity against azocasein increased. Degradative changes were not detected in bacteroids during nodule senescence. Total soluble bacteroid protein per gram of nodule remained constant, and an increase in proteolytic activity in bacteroid extracts was not observed. These results are consistent with the view that soybean nodule bacteroids are capable of redifferentiation into free-living bacteria upon deterioration of the legume-rhizobia symbiosis.

The effect of ammonium nitrate on the synthesis of nitrogenase and the concentration of leghemoglobin in pea root nodules induced by Rhizobium leguminosarum

The effects of NH 4NO 3 on the development of root nodules of Pisum sativum after infection with Rhizobium leguminosarum (strain PRE) and on the nitrogenase activity of the bacteriods in the nodule tissue were studied. The addition of NH 4NO 3 decreased the nitrogenase activity measured on intact nodules. This reduction of nitrogen fixation did not result from a reduced number of bacteroids or a decreased amount of bacteroid proteins per gram of nodule. The synthesis of nitrogenase, measured as the relative amount of incorporation of [ 35S]sulfate into the components I and II of nitrogenase was similarly not affected. The addition of NH 4NO 3 decreased the amount of leghemoglobin in the nodules and there was a quantitative correlation between the leghemoglobin content and the nitrogen-fixing capacity of the nodules. The conclusion is that the decrease of nitrogen-fixing capacity is caused by a decrease of the leghemoglobin content of the root nodules and not by repression of the nitrogenase synthesis.

Ineffectiveness of viomycin-resistant mutants of Rhizobium meliloti.

Under clearly defined conditions one-step acquisition of viomycin resistance by a normally effective strain of Rhizobium meliloti resulted in one-step acquisition of ineffectiveness in nitrogen fixation, which probably occurred with a one-gene change in the R. meliloti genome. Two-step mutants retained their ability to produce root nodules but such nodules also were ineffective. Increased sensitivity of the viomycin-resistant mutants to glycine and D-alanine was not noted. Bacteroids were not seen in nodules formed by the viomycin-resistant mutants on their homologous host plant. Nitrogenase activity was not detected, by acetylene reduction, in detached ineffective nodules, whereas effective nodules formed 10.6 μmoles of ethylene per hour per gram of nodules. Growth of the effective parent strain in a low concentration of viomycin resulted in elongation and swelling of the cells so that they appeared as artificially produced bacteroids. Viomycin-resistant mutants did not undergo this transformation. Antigens could be readily extracted by hot- and cold-saline extraction of wet packed cells of both resistant and sensitive cultures but antigenic differences, which may have indicated cell wall differences, were not noted.