Allantoic Acid Research Articles

Catabolism of caffeine and related purine alkaloids in leaves ofCoffea arabica L.

In a study of purine alkaloid catabolism pathways in coffee,14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves ofCoffea arabica. Incorporation of label into14CO2 was determined and methanol-soluble metabolites were analysed by high-performance liquid chromatography-radiocounting. The data obtained demonstrate catabolism of caffeine → theophylline → 3-methylxanthine → xanthine. Xanthine is degraded further by the conventional purine catabolism pathway to CO2 and NH3 via uric acid, allantoin and allantoic acid. The conversion of caffeine to theophylline is the rate-limiting step in purine alkaloid catabolism and provides a ready explanation for the high concentration of endogenous caffeine found inC. arabica leaves. Although theobromine is converted primarily to caffeine, a small portion of the theobromine pool appears to be degraded to xanthine by a caffeine-independent pathway. In addition to being broken down to CO2, via the purine catabolism pathway, xanthine is metabolised to 7-methylxanthine. Metabolism of [2-14C]xanthine byC. arabica leaves in the presence of 5 mM allopurinol results in very large increases in incorporation of radioactivity into 7-methylxanthine as degradation of the substrate via the purine catabolism pathway is blocked. The identity of 7-methylxanthine in these studies was confirmed by gas chromatography-mass spectrometry analysis.

Urease Is Not Essential for Ureide Degradation in Soybean.

The hypothesis that soybean (Glycine max L. [Merrill]) catabolizes ureides to urea to a physiologically significant extent was tested and rejected. Urease-negative (eu3-e1/eu3-e1) plants were supported by fixed N2 or by 2 mM NH4NO3, so that xylem-borne nitrogen contained predominantly ureides (allantoin and allantoic acid) or amide amino acids, respectively. Seed nitrogen yield was equal on either nitrogen regime, although 35-d-old fixing plants accumulated about 6 times more leaf urea. In callus, lack of an active urease reduced growth on either arginine or allantoin as the sole nitrogen source, but the reduction was greater on arginine (73%) than on allantoin (39%). Furthermore, urease-negative cells accumulated 17 times more urea than urease-positive cells on arginine; for allantoin the ratio was 1.8. Urease-negative callus accumulated urea at 3% the rate of seedlings. To test whether urea accumulating in urease-negative seedlings was derived from ureides, seeds were first allowed to imbibe in 1 mM allopurinol, an inhibitor of ureide formation. Seedling ureides were decreased by 90%, but urea levels were unchanged. Thus, ureides are poor precursors of urea, which was confirmed in seedlings that converted no more than 5% of seed-absorbed [14C-ureido]allantoate to [14C]urea, whereas 40 to 70% of [14C-guanido]arginine was recovered as [14C]urea.

Immunoaffinity Purification and Comparison of Allantoinases from Soybean Root Nodules and Cotyledons

Allantoinase (allantoin amidohydrolase, EC 3.5.2.5) catalyzes the conversion of allantoin to allantoic acid in the final step of ureide biogenesis. We have purified allantoinase more than 4000-fold by immunoaffinity chromatography from root nodules and cotyledons of soybean (Glycine max [L] Merr.). We characterized and compared properties of the enzyme from the two sources. Seed and nodule allantoinases had 80% identity in the first 24 amino acid residues of the N terminus. Two-dimensional gel electrophoresis of the purified enzymes showed that multiple forms were present in each. Allantoinases from nodules and cotyledons had very low affinity for allantoin with a Km for allantoin of 17.3 mM in cotyledons and 24.4 mM in nodules. Both had activity in a broad range of pH values from 6.5 to 7.5. In addition, purified allantoinase from both sources was very heat stable. Enzyme activity was stable after 1 h at 70 degrees C, decreased gradually with heating to 85 degrees C, and was lost at 90 to 95 degrees C. Although these studies have revealed some differences between allantoinases in seeds and nodules, the differences were not reflected in key enzyme properties. The immunoaffinity approach enabled purification of allantoinase from soybean root nodules and simplified its purification from cotyledons, thereby allowing characterization and comparison of the enzyme from the two sources.

Effect of estrone treatment from day 30 to 45 of pregnancy on endometrial protein secretion and uterine capacity

Secretion of proteins by the endometrium of pigs during pregnancy is reported to be influenced by progesterone and estrogen. The effect of estrone treatment from d 30 to 45 of pregnancy on endometrial protein secretion and uterine capacity was tested in unilaterally hysterectomized-ovariectomized (UHO) gilts. Ten intact and 16 UHO crossbred gilts were mated and assigned to the following treatments: 1) intact controls, n = 10; 2) UHO, n = 8; and 3) UHO + estrone (E; two 150-mg implants, 60-d release, implanted on d 30 of gestation), n = 8. Gilts were killed on d 45 of pregnancy. A sample of allantoic fluid was collected from each conceptus. Blood and endometrial tissue samples were collected to evaluate estrone concentrations, and placental and endometrial tissues were incubated to evaluate protein secretion. Estrone treatment increased (P < .01) plasma and endometrial tissue estrone concentrations. Unilateral hysterectomy-ovariectomy decreased (P < .01) fetal survival. No effect of estrone was detected on the number of live fetuses, protein secretion by endometrial tissue in culture, or allantoic fluid protein, acid phosphatase, retinol binding protein, or retinol. Estrone treatment decreased uterine weight (P = .05) and allantoic fluid fructose concentrations (P < .05). After correction for allantoic fluid volume, allantoic fluid protein, retinol, and acid phosphatase activity were decreased (P < .05) in UHO-treated pigs. The UHO treatment did not affect allantoic fluid fructose concentrations. These results indicate that 1) estrone treatment from d 30 to 45 of pregnancy and at the dosage used did not alter endometrial protein secretion or fetal survival, and 2) UHO decreased the amount of endometrial proteins available to conceptuses.

Proposed physiologic functions of boron in plants pertinent to animal and human metabolism.

Boron has been recognized since 1923 as an essential micronutrient element for higher plants. Over the years, many roles for boron in plants have been proposed, including functions in sugar transport, cell wall synthesis and lignification, cell wall structure, carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid metabolism, phenol metabolism and membrane transport. However, the mechanism of boron involvement in each case remains unclear. Recent work has focused on two major plant-cell components: cell walls and membranes. In both, boron could play a structural role by bridging hydroxyl groups. In membranes, it could also be involved in ion transport and redox reactions by stimulating enzymes like nicotinamide adenine dinucleotide and reduced (NADH) oxidase. There is a very narrow window between the levels of boron required by and toxic to plants. The mechanisms of boron toxicity are also unknown. In nitrogen-fixing leguminous plants, foliarly applied boron causes up to a 1000% increase in the concentration of allantoic acid in leaves. In vitro studies show that boron inhibits the manganese-dependent allantoate amidohydrolase, and foliar application of manganese prior to application of boron eliminates allantoic acid accumulation in leaves. Interaction between borate and divalent cations like manganese may alter metabolic pathways, which could explain why higher concentrations of boron can be toxic to plants.

Evaluation of N2 fixation by stem and root nodules in sesbania rostrata during rainy and dry months

Sesbania rostrata is the most popular green manure legumes in Tamilnadu, India.S. rostrata produces both stem and root nodules. Until this time, no experiments had been performed to assess the superiority of one kind of nodule over the other. The levels of nitrogenous compounds, like nitrite, nitrate, total nitrogen, free amino acids, total soluble proteins, total allantoin, total allantoic acid, and total ureides, were determined in both the stem and root nodules during rainy and dry seasons. During the rainy season, the stem nodules possessed heavy deposition of these N-containing compounds than the root nodules. On the other hand, during the dry season, the root nodules accumulated substantial levels of these nitrogenous compounds. In a similar way, the activities of nitrogenase and nitrate reductase were higher in stem nodules during the rainy season, and the trend was reversed during the dry season, the root nodules having more nitrogenase and nitrate reductase. In consonance with the higher activities of enzymes and gorging of nitrogenous compounds, calorific values were more in the stem nodules during the rainy season. The activities of oxygen scavenging enzymes were higher in stem nodules during the dry season, possibly indicating their role in alleviation of H2O2 and O 2 - city to the nodules. As regards rhizobial population, the root nodules always contained moreRhizobia than that of the stem nodules. The efficiency of the stem and root nodules to fix more nitrogen and synthesize nitrogenous compounds is seasonal. In the dry season, the entire role of N2-fixation seemed to be borne by root noduleRhizobia only, since stem nodules during this period are hardly formed and sparsely distributed.

Amphibian allantoinase. Molecular cloning, tissue distribution, and functional expression.

The chain of enzymes necessary to convert uric acid to its metabolic products urea and glyoxylic acid in vertebrates is truncated through the successive loss of allantoicase, allantoinase, and urate oxidase during phylogenetic evolution. Previous studies have assigned the localization of both urate oxidase and allantinase to the peroxisome in the amphibian liver. This study reports the cloning of a cDNA encoding bullfrog (Rana catesbeiana) allantoinase, an enzyme that converts allantoin to allantoic acid. The cDNA is 2112 base pairs in length containing a 1449-base pair open reading frame which corresponds to a 483-residue protein (53,296 Da). Structural analysis of the deduced protein suggested two potential transmembrane segments and the presence of a putative mitochondrial localization sequence in the amino terminus. Immunocytochemical analysis revealed that allantoinase is localized to mitochondria and not to peroxisomes. On Northern blotting, a single mRNA species was detected in the liver and kidney of frog but not in other tissues; this distribution was confirmed by immunoblotting. The hepatic- and renal-specific expression of allantoinase coincides with the distribution of urate oxidase in these tissues in the frog. The allantoinase expressed in Saccharomyces cerevisiae and in Spodoptera frugiperda (Sf9) insect cells exhibits catalytic activity and is antigenically identical to the native frog enzyme.

Ureides and Enzymes of Ureide Synthesis in Flax (Linum usitatissimum) Plants and Seeds

Xanthine oxidoreductase exhibiting a superoxide producing activity (Xanthine: O 2 Oxidoreductase, EC 1.2.3.2), uricase (Urate: O 2 oxidoreductase, EC 1.7.3.3), allantoinase (EC 3.5.2.5) and ureides were detected in leaves, stems, roots and seeds of flax plants. Allopurinol [4-hydroxypyrazolo(3,4-d)pyrimidine], an analogue of purine and tightly binding inhibitor of the xanthine oxidizing enzyme, was applied as soil drench at 0.4 mM starting 7-8 days after planting and reduced the concentration of allantoic acid in leaves and roots by 50%. No further inhibition was obtained using a higher concentration (1.6mM) of allopurinol. These findings indicate that in vivo inhibition of xanthine oxidoreductase took place and that the purine catabolic pathway is active in flax plants. However, since the higher inhibition obtained even at 1.6 mM was only 50%, and considering that no toxic effects were induced by applying 1.6 mM allopurinol, it is supposed that other route/s for ureide synthesis may be active in flax plants.

Analysis of oxonic acid, uric acid, creatine, allantoin, xanthine and hypoxanthine in poultry litter by reverse phase HPLC

A separation method has been developed to extract organic compounds from poultry manure and litter and subsequently analyze these extracts using reverse phase high-pressure liquid chromatography. Specifically, the method may be used to quantify oxonic acid, allantoin, creatine, uric acid, xanthine and hypoxanthine in poultry manure samples. In a representative sample of fresh poultry manure, oxonic acid, allantoin, creatine, uric acid and xanthine were present at concentrations of 2.4, 2.7, 3.9, 270 and 0.8 mg/g dry manure, respectively. Litter samples stored for eight or sixteen weeks showed the presence of hypoxanthine but no longer contained detectable quantities of creatine. Allantoic acid and urea, both previously shown to be present in the litter samples, could not be distinguished by the chromatographic technique. Orotic acid and uracil, although capable of being separated by the method, were not detected in any poultry litter samples.

Purification of Allantoinase from Soybean Seeds and Production and Characterization of Anti-Allantoinase Antibodies

Allantoinase catalyzes the hydrolysis of allantoin to allantoic acid, a reaction important in both biogenesis and degradation of ureides. Ureide production in cotyledons of germinating soybean (Glycine max L.) seeds has not been studied extensively but may be important in mobilizing nitrogen reserves. Allantoinase was purified approximately 2500-fold from a crude extract of soybean seeds by differential centrifugation, heat treatment, ammonium sulfate fractionation, ethanol fractionation, and fast protein liquid chromatography (Pharmacia) with Mono-Q and Superose columns. The purified enzyme had a subunit size of 30 kD. Polyclonal antibodies produced against the purified protein titrated allantoinase activity in a crude extract of seed proteins. Antibodies recognized the 30-kD band in western blot analysis of crude seed extracts, indicating that they were specific for allantoinase.

Purine metabolism and the biosynthesis of caffeine in maté leaves

Purine metabolism and the biosynthesis of purine alkaloids in leaves of maté plants were investigated by administering [8 −14C]adenine,[8 −14C]guanosine and [8 −14C]hypoxanthine to maté plants of different ages. Each precursor was incorporated into theobromine and caffeine in young leaves. No biosynthesis of these purine alkaloids took place in mature dark-green leaves. Pulse-chase experiments and the inhibitory effects of coformycin suggest that the biosynthesis of caffeine from adenine nucleotides is initiated by the reaction catalysed by AMP deaminase. The conventional pathway for the degradation of purines via allantoin and allantoic acid appeared to be operative in both young and mature leaves. No significant degradation of caffeine was detected in the tracer experiments. The levels of adenine nucleotides in young maté leaves were about five times higher than those of guanine nucleotides. Other possible pathways of purine metabolism in maté leaves are discussed.

N-carbamoyl-D-amino acid amidohydrolase from Comamonas sp. E222c purification and characterization.

N-Carbamoyl-D-amino acid amidohydrolase was purified 119-fold, with 36% overall recovery from a cell-free extract of Comamonas sp. E222c. The purified enzyme was homogeneous as judged by SDS/PAGE. The relative molecular mass of the native enzyme was 120,000 and that of the subunit was 40,000. The purified enzyme hydrolyzed various N-carbamoyl-D-amino acids to D-amino acids, ammonia and carbon dioxide. N-Carbamoyl-D-amino acids having hydrophobic groups served as good substrates for the enzyme. The Km and Vmax values for N-carbamoyl-D-phenylalanine were 19.7 mM and 13.1 units/mg, respectively, and those for N-carbamoyl-D-p-hydroxyphenylglycine were 13.1 mM and 0.56 units/mg, respectively. The enzyme strictly recognized the configuration of the substrate and only the D-enantiomer of the N-carbamoyl amino acid was hydrolyzed. The enzyme activity was not significantly affected by N-carbamoyl-L-amino acids and ammonia. The enzyme was sensitive to thiol reagents and did not require metal ions for its activity. The enzyme did not hydrolyze N-carbamoyl-beta-alanine or N-carbamoyl-DL-aspartate suggesting that the enzyme is different from the N-carbamoylamide-hydrolyzing enzymes involved in the pyrimidine degradation pathway. The enzyme did not hydrolyze allantoin and allantoic acid, which are intermediates in purine degradation, N-carbamoylsarcosine and citrulline, suggesting that it is a novel N-carbamoylamide amidohydrolase.

Stability of allantoin and identification of its degradation compounds

The stability of allantoin was studied in pH 3.0, 6.0, and 8.0 buffer solutions at 50 degrees C for 55 d. Allantoin was determined by high performance liquid chromatography (HPLC) with a cation exchange mode and colorimetry. The known degradation compounds, allantoic acid and glyoxylic acid, were simultaneously determined by ion chromatography. Urea was determined by HPLC with an ion pair mode. In the stability studies on pH 6.0 and 8.0 solutions, new degradation compounds of allantoin were identified as two growing unknown peaks in the HPLC chromatogram. Isolation of these compounds by preparative HPLC and 1H, 15N and 13C-NMR spectra revealed that they were condensates of allantoin and glyoxylic acid, which also reacted positively in phenylhydrazine colorimetry. The amounts of these compounds were calculated from the determination results of other allantoin related compounds in the buffer solutions and were estimated as the biggest amount among all other compound. As they were found to be stable in an alkaline solution, conditions for hydrolysis in the colorimetric determination of allantoin were further examined. It was found that the longer hydrolysis gave more than 90% recovery in the colorimetry.

Analysis of apoplastic solutes in the cortex of soybean nodules

Various techniques were used to extract solutes from the free space of intact soybean [Glycine max (L.) Merr.] nodules. A variety of solutes (carbohydrates, amino acids, organic acids, ions) was found, but the major solute obtained with all methods was allantoic acid. Most work was done with a technique involving vacuum infiltration of intact detached nodules with water. This approach provided rapid sampling of the apoplastic solutes, and the results indicated that solutes were not derived from the xylem and phloem of ruptured vascular bundles. Infiltration of intact nodules with Fast Green showed dye penetration only to the barrier in the inner cortex, indicating that infected tissues did not contribute to solute composition. Although allantoic acid was the only ureide which could be detected in solute samples, no evidence was obtained for the presence of allantoinase in the cortical apoplast. The results suggest the transport of allantoic acid by an apoplastic route in nodules or the release of allantoic acid to the cortical apoplast in response to treatments which disrupt ureide export. Calculated values for solute concentrations in the cortical apoplast were in the hundred millimolar range, suggesting that apoplastic solutes may represent a significant osmotic component in the nodule cortex.

Effect of NO3 on N2 fixation and nitrogenous solutes of xylem in two nodulated West African geocarpic legumes, Kersting's bean (Macrotyloma geocarpum L.) and Bambara groundnut (Vigna subterranea L.)

Nodulation, nitrogen (N2) fixation and xylem sap composition were examined in sand cultured plants of Bambara groundnut (Vigna subterranea L.) and Kersting's bean (Macrotyloma geocarpum L.) inoculated with Bradyrhizobium strain CB756 and supplied via the roots for a 4 week period from the third week onwards with different levels of (15N)-nitrate (0–15 mM). The separate contributions of nitrate and N2 to plant nitrogen were measured by isotope dilution. Increasing levels of nitrate inhibited nodule growth (measured as dry matter or nodule N) of both species parallel with decreased dependence on symbiotically-fixed N. Specific nodule activity (N2 fixed g nodule dry−1 d−1 of nodules) was reduced progressively with time in V. subterranea at higher (5 or 15 mM) levels of NO3, but this was not so for M. geocarpum. Root xylem bleeding sap of both species showed ureides (allantoin and allantoic acid) as predominant (>90%) solutes of nitrogen when plants were relying solely on atmospheric N. Levels of ureide and glutamine decreased and those of asparagine and nitrate in xylem increased with increasing level of applied nitrate. Relative levels of xylem ureide-N were positively correlated (R2=0.842 for M. geocarpum and 0.556 for V. subterranea), and the ratio of asparagine to glutamine in xylem exudate negatively correlated (R2=0.955 for M. geocarpum and 0.736 for V. subterranea) with plant reliance on nitrogen fixation. The data indicate that xylem sap analyses might be useful for indirect field assays of nitrogen fixation by the species and that Kersting's bean might offer some potential as a symbiosis in which N2 fixation is relatively tolerant of soil N.

Re‐evaluation of the role of ureides in the xylem transport of nitrogen in Arachis species

There are conflicting reports in the literature of the possible role of the ureides, allantoin and allantoic acid, in the nitrogen economy of Arachis species. Therefore, xylem sap composition in food peanut (Arachis hypogaea L.), and two forage peanuts (A. pintoi L. and A. glabrata Benth.) has been studied in detail. Xylem saps were collected from peanuts grown under different nutritional regimes and environmental conditions in the glasshouse and field in Australia, Malaysia and Indonesia, and the N‐containing solutes analysed. The relative amounts and concentrations of ureides in these peanut exudates were compared with those of soybean (Glycine max [L.] Merr.) – a species known to export ureides in its xylem stream as the major product of N2 fixation.Xylem concentrations of ureides in soybean were high in N2‐fixing plants (2.9 to 3.7 μmol ml−1), representing 60 to 88% of xylem solute nitrogen, but it contributed only 9% (0.7 μmol ml−1) if plants were unnodulated and supplied nitrate. In all species of peanut, concentrations of ureides measured in xylem sap were generally much smaller (0.02 to 0.37 μmol ml−1; 1–7% of xylem nitrogen) and were unaffected by peanut species or cultivar, rhizobial strain, plant size, growth rate, or stage of development, and were not related to N2 fixation (less than 0.1% of currently fixed nitrogen exported as ureides) or the assimilation of nitrate. Apparently high levels of ureides in sap from some field‐grown plants were shown to be due to interference with the ureide colorimetric assay by some contaminating compound rather than represent increased ureides per se.

Effect of rust infection on levels of uricase, allantoinase and ureides in susceptible and hypersensitive bean leaves

The enzymatic activities involved in two sequential steps of purine catabolism and ureide biosynthesis, i.e. uricase, catalase and allantoinase, were determined in susceptible and hypersensitive bean leaf tissue after infection with Uromyces phaseoli. Uricase increased to approx. two times more than the control value 20–22 h after inoculation of the hypersensitive cv. K.W. 765 (reaction grade 2 ++) close to pathogen penetration and first haustoria formation and, 1 day later, in the susceptible cvs Golden Gate Wax, Pinto 111 (reaction grade 6) and in the hypersensitive cv. K.W. 814 (reaction grade 1). Afterwards, the highest increases in uricase activity (up to 10 times the control), mainly localized in fractions of leaf homogenate sedimenting at 2000 g and 15000 g , were detected in c.v. K.W. 765 during lesion development, indicating that a peroxisome-associated enzyme was involved. Lower increases (up to two to three times the control) were observed in the susceptible cultivars during stroma differentiation (flecks) and uredospore formation. Catalase linked to the particulate fractions increased in susceptible cultivars to the same extent as uricase from 2 to 6 days after inoculation. Also in cv. K.W. 765 it increased during lesion development, but very much less than uricase, with the consequence that a possible toxic action, due to unscavenged H 2O 2 production, could arise during hypersensitivity expression. An enhancement of allantoinase two or three times the control values during stroma differentiation was detected in susceptible cultivars. By contrast, allantoinase activity was unchanged during local lesion formation in cv. K.W. 765, indicating that the activation of this enzyme is specifically involved during the establishment of a biotrophic relationship between Phaseolus vulgaris and Uromyces phaseoli. In the susceptible cultivar, an increase in allantoic acid during the late stages of infection (uredospores differentiation) was observed. Both allantoin and allantoic acid were enhanced during lesion development in the hypersensitive cultivar. The results are consistent with the interpretation that the enhanced purine catabolism in rust-infected bean leaves is connected both to a nutritional benefit for the parasite in the compatible relationship, and to a toxic effect for the host in the incompatible one.

Catabolism of adenine nucleotides in suspension-cultured plant cells

Profiles of the catabolism of adenine nucleotides in cultured plant cells were investigated. Adenine nucleotides, prelabelled by incubation of suspension-cultured Catharantus roseus cells with [8-14C]adenosine, were catabolized rapidly and most of the radioactivity appeared in 14CO2. Allantoin and allantoic acid, intermediates of the oxidative catabolic pathway of purines, were temporarily labelled. When the cells, prelabelled with [8-14C]adenosine, were incubated with high concentrations of adenosine, the rate of catabolism of adenine nucleotides increased. The results suggest that the relative rate of catabolism of adenine nucleotides is strongly dependent on the concentration of adenine nucleotides in the cells. Studies using allopurinol, coformycin and tiazofurin, inhibitors of enzymes involved in purine metabolism, suggest that participation of AMP deaminase and xanthine oxidoreductase in the catabolism of adenine nucleotides in plant cells. AMP deaminase was found in extracts from C. roseus cells and its activity increased significantly in the presence of ATP. In contrast, no adenosine deaminase or adenine deaminase activity was detected. Qualitative differences in the catabolic activity of AMP were observed between suspension-cultured cells from different species of plants.

Distribution and Metabolism of Xylem-Borne Ureido and Amino Compounds in Developing Soybean Shoots

Pulse-chase feeding (30-120 minutes) of (14)C-labeled nitrogenous compounds to cut transpiring shoots was used to investigate the early fate of the major xylem-borne solutes in N(2)-fixing soybean (Glycine max) plants at the V(4) growth stage. By comparison with the foliar distribution of [(14)C]inulin (a xylem marker), it was determined that the phloem supply of allantoin, allantoic acid, asparagine, glutamine, aspartate, and arginine, respectively, provided about 20, 10, three, two, five, and 20 times the (14)C delivered to the developing trifoliolate in the xylem stream. Recovery of unmetabolized asparagine, aspartate, and arginine in this indicator trifoliolate, and significant declines in the percentage of (14)C from allantoic acid and allantoin recovered in the first trifoliolate, provided some support for the direct xylem-to-phloem transfer of these compounds, but did not preclude the involvement of indirect transfer. Data on stem retention and foliar distribution, expressed as a function of the relative xylem sap composition, indicated that ureides provide the major sources of nitrogen to all plant parts. There was no consistent distinction in distribution patterns between pairs of similar anionic and neutral compounds. The extent of xylem-to-phloem transfer among the ureido or the amino compounds was inversely related to its prominence in xylem sap.

Sesbaniaspp.,Aeschynomene indicaandCrotalariaspp. are amide-exporters

Abstract Extract Leguminous plants consist of two groups, amide-exporting and ureide-exporting plants. The former legumes export a large fraction of fixed-N in the form of amides (asparagine and glutamine), and the latter legumes in the form of ureides (allantoic acid and allantoin). Another characteristic of the nodules is the enrichment in 15N. There are two types of legumes: one characterized by the enrichment with 15N in N2-fixing nodules, in contrast to the other where the enrichment does not occur. The first investigation by Shearer et al. (1982) suggested that the nodules exporting fixed-N in the form of ureides were enriched in 15N unlike those exporting it in the form of amides. Soybeans, mungbean, and cowpea belong to the former group and groundnut, alfalfa, white clover to the latter. Although pea and faba bean were first classified into the latter group (Shearer et al. 1982), a recent investigation (Yoneyama 1988) showed that these nodules were also enriched in 15N.