Ureide Accumulation Research Articles

Drought-induced changes in free amino acid and ureide concentrations of nitrogen-fixing chickpea

The metabolic products of nitrogen (N) fixation in a legume can be amides or ureides. Chickpea (Cicer arientinum L.) is a cool-season legume which transports both ureides and amides from N fixation. Ureides are purine derivatives which are synthesized solely in the nodules. Drought-sensitive legumes accumulate ureides, but the regulation of these N fixation products during drought in chickpea is not yet known. The objectives of this study were (1) to measure the metabolic products of N fixation during drought and (2) to quantify the differences in N fixation among chickpea cultivars during drought by acetylene reduction activity under controlled environment conditions. Five chickpea cultivars were exposed to drought by soil dehydration. Plants were harvested at 1, 5, 10 and 15 d after drought and were analyzed for leaf and stem ureide concentrations and total N. In separate growth chamber experiments, N fixation was quantified daily. Leaf ureide and free amino acid concentrations were analyzed at 1, 5, and 15 d after drought. Drought increased ureide accumulation in drought-sensitive cultivars and decreased total N, alanine and asparagine concentrations over time. Drought-tolerant chickpea cultivars maintained ureide and amide concentrations during drought. Of the chickpea cultivars examined, Myles was the most drought tolerant and CDC Chico was the least. Further research on leaf ureides, alanine and asparagine concentrations would be valuable to determine if these metabolic products could serve as measures for screening chickpea germplasm for drought-tolerant N fixation. Key words: Ureides, N fixation, Asparagine, Acetylene reduction

Update on ureide degradation in legumes

Warm season N2-fixing legumes move fixed N from the nodules to the aerial portions of the plant primarily in the form of ureides, allantoin and allantoate, oxidation products of purines synthesized de novo in the nodule. Ureides are also products of purine turnover in senescing tissues, such as seedling cotyledons. A combination of biochemical and molecular approaches in both crop and model species has shed new light on the metabolic pathways involved in both the synthesis and degradation of allantoin. Improved understanding of ureide biochemistry includes two 'additional' enzymatic steps in the conversion of uric acid to allantoin in the nodule and the mechanism of allantoin and allantoate breakdown in leaf tissue. Ureide accumulation and metabolism in leaves have also been implicated in the feedback inhibition of N2-fixation under water limitation. Sensitivity to water deficit differs among soybean cultivars. Manganese supplementation has been shown to modify relative susceptibility or tolerance to this process in a cultivar-dependent manner. A discussion of the potential roles for ureides and manganese in the feedback inhibition of N2-fixation under water limitation is presented. The existing data are examined in relation to potential changes in both aerial carbon and nitrogen supply under water deficit.

Soybean Genotypic Difference in Growth, Nutrient Accumulation and Ultrastructure in Response to Manganese and Iron Supply in Solution Culture

The objective of this research was to characterize the physiology and cell ultrastructure of two soybean genotypes subjected to nutrient solutions with increasing concentrations of manganese (Mn) at two contrasting iron (Fe) concentrations. Genotypes 'PI227557' and 'Biloxi' were selected based on their distinctly different capacities to accumulate Mn and Fe. * Bradyrhizobium-inoculated plants were grown in hydroponic cultures in a greenhouse. Nutrient solutions were supplied with Mn concentrations ranging from 0.3 to 90 microm, at either 5 or 150 microm Fe as FeEDTA. * For both genotypes and at both Fe concentrations, Mn concentrations from 6.6 to 50 microm did not affect shoot, root and nodule mass, or leaf and nodule ureide concentration. Mn concentrations of 70 and 90 microm did not result in visible toxicity symptoms, but hindered growth and nodulation of 'Biloxi'. An Mn concentration of 0.3 microm was, however, deleterious to growth and nodulation for both genotypes, and caused an accumulation of ureides in leaves and major alterations in the ultrastructure of chloroplasts, nuclei and mitochondria, regardless of the Fe concentration. In 'PI227557', there was also a proliferation of Golgi apparatus and endoplasmic reticulum in the cytoplasm of leaf cells, and nodules showed disrupted symbiosomes lacking poly-beta-hydroxybutirate grains concomitantly with a proliferation of endoplasmic reticulum as well as arrested bacterial division. At 15 microm Fe, ferritin-like crystals were formed in the lumen of chloroplasts of 'PI227557' plants. For both genotypes, there was an antagonism between the Fe and Mn concentrations in leaves, the higher values of both microelements being detected in 'PI227557'. The absence of any detectable relationship between Fe or Mn and zinc, phosphorus and copper concentrations in leaves ruled out those micronutrients as relevant for Mn and Fe nutrition in soybeans. * The results confirmed the greater capacity of 'PI227557' for Mn and Fe accumulation than 'Biloxi' for most nutrient treatments. Hence, 'PI227557' may be a very useful genetic resource both in developing soybean cultivars for growth on low nutrient soils and in physiological studies to understand differing approaches to nutrient accumulation in plants.

Ureide Accumulation in Response to Mn Nutrition by Eight Soybean Genotypes with N 2 Fixation Tolerance to Soil Drying

Nitrogen fixation in soybean (Glycine max Merr.) is especially sensitive to soil drying. The basis of this sensitivity appears to be related to the fact that ureides are transported from the nodules, and the ureide concentrations increase with water deficits in leaves resulting in an apparent feedback to nodules involving ureides that inhibit activity. Therefore, sustained ureide catabolism in the leaves under water deficit appears to be critical for N fixation tolerance. Recently, eight plant introduction lines were identified that expressed substantial N fixation tolerance of water deficits. The focus of this study was to explore the basis for the tolerance previously observed in the eight lines. Specifically, the objective of this study was to evaluate in these genotypes the dependence for ureide catabolism on allantoate amidinohydrolase, which in other cultivars appears to be related to N fixation tolerance of water deficits. Since allantoate amidinohydrolase does not require Mn as a co-factor in contrast to the alternate enzyme for allantoic acid catabolism, ureide accumulation was measured in leaves of these genotypes after the plants were fed allantoic acid following growth on low Mn hydroponic solutions. This treatment confirmed that ureide accumulation was independent of Mn nutrition level in six of the eight tolerant lines. Ureide accumulation in PI 429328 was consistently the most insensitive to Mu nutrition level. Overall, these results indicated that ureide catabolism independent of Mn is active in six of the eight plant introduction lines identified to express N fixation tolerance to soil drying.

Ureide Accumulation in Response to Mn Nutrition by Eight Soybean Genotypes with N Fixation Tolerance to Soil Drying

Nitrogen fixation in soybean (Glycine max Merr.) is especially sensitive to soil drying. The basis of this sensitivity appears to be related to the fact that ureides are transported from the nodules, and the ureide concentrations increase with water deficits in leaves resulting in an apparent feedback to nodules involving ureides that inhibit activity. Therefore, sustained ureide catabolism in the leaves under water deficit appears to be critical for N2 fixation tolerance. Recently, eight plant introduction lines were identified that expressed substantial N2 fixation tolerance of water deficits. The focus of this study was to explore the basis for the tolerance previously observed in the eight lines. Specifically, the objective of this study was to evaluate in these genotypes the dependence for ureide catabolism on allantoate amidinohydrolase, which in other cultivars appears to be related to N2 fixation tolerance of water deficits. Since allantoate amidinohydrolase does not require Mn as a co-factor in contrast to the alternate enzyme for allantoic acid catabolism, ureide accumulation was measured in leaves of these genotypes after the plants were fed allantoic acid following growth on low Mn hydroponic solutions. This treatment confirmed that ureide accumulation was independent of Mn nutrition level in six of the eight tolerant lines. Ureide accumulation in PI 429328 was consistently the most insensitive to Mn nutrition level. Overall, these results indicated that ureide catabolism independent of Mn is active in six of the eight plant introduction lines identified to express N2 fixation tolerance to soil drying.

Evidence that carbon dioxide enrichment alleviates ureide-induced decline of nodule nitrogenase activity.

The hypothesis that elevated [CO(2)] alleviates ureide inhibition of N(2)-fixation was tested. Short-term responses of the acetylene reduction assay (ARA), ureide accumulation and total non-structural carbohydrate (TNC) levels were measured following addition of ureide to the nutrient solution of hydroponically grown soybean. The plants were exposed to ambient (360 micromol mol(-1)) or elevated (700 micromol mol(-1)) [CO(2)]. Addition of 5 and 10 mM ureide to the nutrient solution inhibited N(2)-fixation activity under both ambient and elevated [CO(2)] conditions. However, the percentage inhibition following ureide treatment was significantly greater under ambient [CO(2)] as compared with that under elevated [CO(2)]. Under ambient [CO(2)] conditions, ARA was less than that under elevated [CO(2)] 1 d after ureide treatment. Under ambient [CO(2)], the application of ureide resulted in a significant accumulation of ureide in all plant tissues, with the highest concentration increases in the leaves. However, application of exogenous ureide to plants subjected to elevated [CO(2)] did not result in increased ureide concentration in any tissues. TNC concentrations were consistently higher under elevated [CO(2)] compared with those under ambient [CO(2)]. For both [CO(2)] treatments, the application of ureide induced a significant decrease of TNC concentrations in the leaves and nodules. For both leaves and nodules, a negative correlation was observed between TNC and ureide levels. Results indicate that product(s) of ureide catabolism rather than tissue ureide concentration itself are critical in the regulation of N(2)-fixation.

Leaf ureide degradation and N2 fixation tolerance to water deficit in soybean1

Accumulation of ureides in leaves is associated with the sensitivity of N(2) fixation in soybean to soil water deficit. Consequently, ureide degradation in leaves may be a key to increasing soybean tolerance to dry soils. Previous research indicated that allantoic acid degradation is catalysed by different enzymes in cultivars Maple Arrow and Williams. The enzyme found in Williams requires manganese as a cofactor. The first objective of this study was to determine if the two degradation pathways were associated with differences in N(2) sensitivity to soil water deficits. N(2) fixation of Williams grown on low-Mn soil was sensitive to stress, but it was relatively tolerant when grown on soil amended with Mn. N(2) fixation in Maple Arrow was relatively tolerant of soil drying regardless of the Mn treatment. The second objective of this study was to expand the study of the degradation pathway to nine additional genotypes. Based on ureide degradation in the presence and absence of Mn, these genotypes also segregated for the two degradation pathways. Those genotypes with the Mn-dependent pathway tended to have drought-sensitive N(2) fixation, but there was one exception. The genotypes not requiring Mn for ureide degradation were drought-tolerant except for one genotype. These results demonstrated the possibility for increasing N(2) fixation tolerance to soil water deficits in soybean by selection of lines with high ureide degradation rates, which were commonly associated with the Mn-independent pathway.

Asparagine and ureide accumulation in nodules and shoots as feedback inhibitors of N2 fixation in soybean

Inhibition of N2 fixation under water deficits has been hypothesized to result from N feedback within the plant involving ureides and/or asparagine (Asn). This study was undertaken to investigate ureide and Asn accumulation in shoots and nodules in response to treatments inhibiting nodule activity (acetylene reduction assay, ARA) such as Asn, ureide, or polyethylene glycol application to the nutrient solution of plants, boric acid on leaves, and imposition of a water deficit. ARA inhibition and nodule concentration of Asn and ureide were correlated to the ureide treatment applied (3–15 mM applied in the nutrient solution). Supplying Asn (3–9 mM applied in the nutrient solution) also induced an increase in nodule Asn and ureide concentration, which was associated with ARA inhibition. Spraying boric acid on leaves also inhibited ARA in parallel to an increase in shoot ureide and nodule Asn concentration while nodule ureide remained unchanged. By contrast, polyethylene glycol (PEG) inhibited ARA in parallel to an increase in nodule Asn and ureide concentration while shoot ureide was unchanged. The decline in ARA in response to water deficit was associated with an increase in nodule ureide, Asn and aspartate (Asp), although the increases in Asn and Asp were less than for ureides. Altogether, the results of these experiments indicated that Asn cannot be the only compound involved in the feedback inhibition of ARA. Instead ureide and Asn are probably both involved, either directly by accumulation of products that fail to be exported, or by feedback from the shoot due to an N‐compound supply that exceeds shoot requirements.

Ureide degradation pathways in intact soybean leaves1

Ureides dramatically accumulate in shoots of N(2)-fixing soybean (Glycine max L. Merr.) under water deficit and this accumulation is higher in cultivars that have N(2) fixation that is sensitive to water deficit. One possible explanation is that ureide accumulation is associated with a feedback inhibition of nitrogenase activity. A critical factor involved in ureide accumulation is likely to be the rate of ureide degradation in the leaves. There exists, however, a controversy concerning the pathway of allantoic acid degradation in soybean. Allantoate amidinohydrolase was reported to be the pathway of degradation in studies using the cultivar Maple Arrow and allantoate amidohydrolase was the pathway that existed in the cultivar Williams. This investigation was undertaken to resolve the existence of these two pathways. An in situ technique was developed to examine the response of ureide degradation in leaf tissue to various treatments. In addition, the response of ureide accumulation and N(2) fixation activity was measured for intact plants in response to treatments that differentially influenced the two degradation pathways. The results from these studies confirmed that Maple Arrow and Williams degraded allantoic acid by different pathways as originally reported. The existence of two degradation pathways within the soybean germplasm opens the possibility of modifying ureide degradation to minimize the influence of soil water deficits on N(2) fixation activity.

Soybean Cultivar Differences in Ureides and the Relationship to Drought Tolerant Nitrogen Fixation and Manganese Nutrition

Water deficit in soybean [Glycine max (L.) Merr.] results in the accumulation of the products of N2 fixation (ureides) in shoots, and this may lead to feedback inhibition of N2 fixation. Manganese is required for ureide degradation in leaves, and it was hypothesized that increased leaf Mn+2 would alleviate ureide accumulation during drought, lessen feedback inhibition, and prolong N2 fixation. In a growth chamber experiment, ureides supplied through roots decreased N2 fixation in well‐watered plants, and a soybean cultivar with demonstrated tolerance of N2 fixation to water deficit (Jackson) had a lesser concentration of shoot ureides following exogenous ureide application than a cultivar sensitive to water deficit (KS4895). In a greenhouse experiment, N2 fixation in Jackson under moderate water deficit was not different from the control in the absence or presence of soil‐applied Mn+2, whereas N2 fixation in KS4895 was 30% of the control in the absence of soil‐applied Mn+2 and 111% of the control in the presence of soil‐applied Mn+2 Increased N2 fixation in KS4895 with soil‐applied Mn+2 under water deficit was associated with decreased shoot ureide concentration. In field experiments, Jackson consistently had lesser shoot ureide concentrations than did KS4895, and enzymatic degradation of ureides was greater for Jackson on one date than for KS4895. We concluded that ureides inhibit N2 fixation, that genetic variation in the ability to degrade ureides may be important in drought tolerance, and that increased leaf Mn+2 concentration promotes ureide breakdown and prolongs N2 fixation under water deficit.

Effect of exogenous NH4 +-N supply on distribution of ureide content in various tissues of alfalfa plants, Medicago sativa

The profile of ureide (allantoin and allantoic acid) accumulation in various tissues of alfalfa, Medicago sativa, was surveyed under different nitrogen nutrient conditions. In the xylem sap, the ratio of ureides to asparagine of two amide type legumes, alfalfa and Lotus corniculatus, was 14 times lower than that of a typical ureide type legume, soybean when they grew in a nitrogenfree nutrient solution. In alfalfa plants, the ureide concentration was higher in the lateral roots and in the nodules than in other tissues. In the main root the concentration of ureide increased gradually towards the root tip. This distribution of ureides, except for the nodule tissues, was similar to that of the non-nodulating soybean variety. Application of ammonium sulfate to the root system slightly increased the ureide content in various tissues of alfalfa in the short term, while the ureide content in the nodule tissues rather decreased after the treatment. The data indicated that ureide accumulation mainly occurred in roots and leaves in the case of alfalfa in the same way as in non-nodulating soybean plants, although the content was much lower than in soybean nodules.

Xanthine degradation and related enzyme activities in leaves and fruits of two coffea species differing in caffeine catabolism.

The degradation of xanthine was studied in young and aged leaves and in immature and mature fruits of Coffea arabica and Coffea dewevrei, which differ with respect to caffeine catabolism. Radioisotope feeding experiments showed that leaves degraded xanthine more readily than fruits but that mature fruits and aged leaves were less efficient than younger tissues. In all cases, a significant part of the recovered radioactivity was in the ureides. Xanthine dehydrogenase was characterized as the enzyme responsible for xanthine degradation, and its activity and that of uricase were consistent with the results obtained in the radioisotope feeding experiments. Activities of allantoinase and allantoate amidohydrolase could not be detected. Considerable levels of endogenous allantoin and allantoic acid were found in fruits and leaves. Therefore, ureide accumulation might be a consequence of low enzyme activity. There was no positive correlation between urease activity and the data from the radioisotope feeding experiments.

Nitrate levels and stages of growth in hypernodulating mutants of Lupinus albus. II. Enzymatic activity and transport of N in the xylem sap

The enzymatic study and transport of N in the xylem sap was carried out with a view to observing the influence of different nitrate levels and growth stages of the plant in chemically treated mutants of Lupinus albus. Several stresses induce a reduction in plant growth, resulting in the accumulation of free amino acids, amides or ureides, not only in the shoot, but also in the roots and nodules. Although enzyme activity is decisive in avoiding products that inhibit nitrogenase by ammonium, little is known about the mechanism by which the xylem carries these products. However, this process may be the key to the function of avoiding the accumulation of amino acids in the cells of infected nodules. The behaviour of the enzymes nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPC), glutamine synthetase (GS) and nitrogen compounds derived from fixation, such as N-<FONT FACE="Symbol">a</font>-amino, N-ureides and N-amide in mutant genotypes were observed. The NR enzyme activity was highly influenced by the application of nitrate showing much higher values than those in the non-application of nitrate, independently of genotype, being that the NR, the best evaluation period was in the tenth week. The L-62 genotype characterized with nitrate- resistance, clearly showed that the enzyme PEPC is inhibited by presence of nitrate. The L-135 genotype (nod- fix-) showed GS activity extremely low, thus demonstrating that GS is an enzyme highly correlated with fixation. With regard to the best growth stage for GS, Lupinus albus should be evaluated in the seventh week.

Involvement of ureides in nitrogen fixation inhibition in soybean

The sensitivity of N2 fixation to drought stress in soybean (Glycine max Merr.) has been shown to be associated with high ureide accumulation in the shoots, which has led to the hypothesis that N2 fixation during drought is decreased by a feedback mechanism. The ureide feedback hypothesis was tested directly by measuring the effect of 10 mM ureide applied by stem infusion or in the nutrient solution of hydroponically grown plants on acetylene reduction activity (ARA). An almost complete inhibition of ARA was observed within 4 to 7 d after treatment, accompanied by an increase in ureide concentration in the shoot but not in the nodules. The inhibition of ARA resulting from ureide treatments was dependent on the concentration of applied ureide. Urea also inhibited ARA but asparagine resulted in the greatest inhibition of nodule activity. Because ureides did not accumulate in the nodule upon ureide treatment, it was concluded that they were not directly inhibitory to the nodules but that their influence mediated through a derivative compound, with asparagine being a potential candidate. Ureide treatment resulted in a continual decrease in nodule permeability to O2 simultaneous with the inhibition of nitrogenase activity during a 5-d treatment period, although it was not clear whether the latter phenomenon was a consequence or a cause of the decrease in the nodule permeability to O2.

Ureide concentration of field‐grown soybean in response to drought and the relationship to nitrogen fixation

Ureides accumulate in soybean (Glycine max [L.] Merr.) petioles during drought under greenhouse conditions despite decreased N2 fixation and ureide production. Field experiments with water‐deficit treatments were established to examine the possibility of ureide accumulation under natural drought‐stress conditions. Tissue ureide concentration of drought tolerant ‘Jackson’ were compared with either ‘Hutcheson’ or ‘Biloxi’. For mild water‐deficit conditions, petiole ureide levels were greater than a well‐watered treatment at ten sampling dates for Hutcheson compared to three dates for Jackson. At only two dates were there significant differences between genotypes in petiole ureide concentration, in which case petiole ureide concentration of Hutcheson was greater than Jackson. Under more severe water‐deficit conditions, there were greater and more consistent increases in petiole ureide concentration for Jackson and Biloxi. Jackson, however, had lower petiole ureide concentration than Biloxi throughout the measurement period for both well‐watered and water‐deficit treatments. Ureide catabolism in leaves during reproductive development was found to be negatively associated with petiole ureide concentration of Hutcheson (r=‐0.37, P=0.01), but not in Jackson (r=‐0.12, P=0.44). These results indicated that increased ureide accumulation in response to water deficits experienced under field conditions was negatively associated with drought tolerance of N2 fixation in these cultivars, and that petiole ureide accumulation may result from decreased ureide catabolism.

Soybean nodulation and N2 fixation response to drought under carbon dioxide enrichment

The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two short‐term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 μmol CO2 mol–1. Under drought‐stressed conditions, elevated [CO2] resulted in a delay in the decrease in N2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2]. The total non‐structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought‐induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation.

Processes Contributing to N2‐Fixation Intensitivity to Drought in the Soybean Cultivar Jackson

Previous research has shown that N2 fixation in soybean [Glycine max (L.) Merr.] is sensitive to drought and begins to decrease at relatively high soil water contents. The fact that N2 fixation rates decrease with soil water deficits in advance of other physiological processes causes an important constraint on soybean performance. Recent evidence, however, indicates possible genetic variation within soybean for this trait. The cultivar Jackson reportedly has N2 fixation activity that was relatively drought insensitive. The objective of this research was to investigate the physiological basis of this unique response in Jackson in comparison with the drought‐sensitive cultivar Biloxi. Experiments were carried out with plants grown in pots in a greenhouse and exposed to drought by soil dehydration. The drought tolerance of N2 fixation in Jackson was confirmed, as well as in one of its parents, ‘Volstate’. Interestingly, Jackson as either the rootstock or scion in grafting studies conferred drought tolerance. Enriching the atmosphere with oxygen around the nodules resulted in a complete recovery of nodule activity in moderately drought‐stressed plants and in partial recovery as the stress severity increased. Elevated oxygen also induced a substantial stimulation of acetylene‐reduction rates in Jackson well‐watered plants. Finally, Jackson was found to have lower levels of ureides in petioles in well‐watered plants than in a sensitive cultivar, and the accumulation of ureides under drought was much less in Jackson. These results demonstrated that N metabolism, physiology, and genetic background are important in accounting for unique behavior of N2 fixation in Jackson under water‐deficit conditions.

Changes in ureide synthesis, transport and assimilation following ammonium nitrate fertilization of nodulated Soybeans

Abstract The effect of ammonium nitrate fertilization on ureide synthesis, xylem transport and assimilation was examined in four week old nodulated soybean plants. In nodules the activity of 5‐phosphoribosylpyrophosphate amidotransferase, a key enzyme of ureide biosynthesis, declined 75%, while enzymes of purine oxidation (xanthine dehydrogenase and uricase) showed no response to nitrogen treatment. Xylem sap concentrations of allantoin and allantoate, as compared to untreated controls, were reduced by about 85% and 65%, respectively. Despite the substantial decline in ureide synthesis and transport, allantoate concentration in leaves of ammonium nitrate treated plants increased by about three‐fold. No ureide accumulation was observed in leaf tissue following a suppression of ureide formation in nodules by allopurinol, an inhibitor of xanthine dehydrogenase. In the pathway of ureide assimilation in leaves, application of inorganic nitrogen had no effect on activity of allantoinase, but caused a 50% drop i...

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.

INFLUENCE OF RHIZOBIAL INOCULATION AND MICRONUTRIENTS APPLICATION ON THE PRODUCTION OF NITROGEN TRANSPORTING COMPOUNDS IN GREENGRAM (Vigna radiata L. WILCZEK)

Seed inoculation with rhizobial strains have significantly enhanced the production and accumulation of nitrogen transporting compounds (Ureides) over untreated control in CO 5 greengram. Among the plant parts, maximum ureide production was observed at nodules and was effectively translocated to flowers and pods through root, stem and leaves. Among the strains inoculated better effect was recorded by GG 2 followed by the other tuo strains. Maximum translocation and accumulation of ureides were recorded in leaves, stem, root and flowers at 45 DAS, whereas in pods it was found to accumulate at 60 DAS. Incorporation of Fe at 0.5 mM and Mo at 0.5 μM enhanced ureide production in the different parts of greengram.