Amino Acids In Xylem Sap Research Articles

Growing medium soluble carbon and nitrogen influence xylem sap and soluble solid contents in greenhouse cucumber fruits

Compelling evidence recently demonstrated that plants can take up nitrogen (N) as organic molecules. Yet, very little research addressed this issue in the context of organic horticulture, where N is provided as organic residues. Organic N and carbon (C) transported from roots to shoots could contribute significantly to the plant C and N accumulation. We posited that the type (organic or mineral) and amount of N fertilization affect the soluble organic N and C content of the growing medium, in turn influencing xylem sap N and C and fruit soluble solids content (SSC). To test this hypothesis, we collected growing medium, xylem sap, and fruit samples in a greenhouse cucumber crop grown in a peat-based growing medium and fertilized with organic (blood and feather meals) or mineral (ammonium nitrate) N fertilizers. The organic N source reduced growing medium concentrations of soluble mineral and organic N relative to the mineral source through microbial immobilization. Xylem sap C and N were positively linked to the soluble C and N contents of the growing medium, contributing to higher fruit SSC. A causal model is proposed, in which 62.6% of the variance observed in fruit SSC is explained by variation in mineral soluble N and soluble organic C in the growing medium and dissolved organic C and amino acids in xylem sap. Our results provide in situ indications that organic molecules in the growing medium are taken up by cucumber plants and contribute to fruit soluble solids in a context relevant to greenhouse horticulture.

Soil nitrogen recovery and seasonal changes of xylem sap amino acids of Amazonian tree species following pasture abandonment

We conducted this study to understand the dynamics of revegetation by examining the levels of mineral nitrogen (NO3− and NH4+) in soil and the capacity of nitrogen use by the principal species growing in secondary forest in central Amazonia. For this, we measured the nitrate and ammonium content of soil, leaves and xylem sap, nitrate reductase activity of the leaves and free amino acid contents of the xylem sap in five tree species (Vismia cayennensis, Vismia japurensis, Bellucia dichotoma, Laetia procera and Goupia glabra) over a chronosequence during recovery after pasture abandonment at two seasons. Soil ammonium was higher in the dry season and nitrate higher in the wet season and increased these with pasture abandonment age. V. japurensis, B. dichotoma and G. glabra decreased foliar ammonium due to pasture abandonment in the dry season and foliar ammonium increased in L. procera in the wet season. V. japurensis and V. cayennensis showed a decrease in nitrate reductase activity, while B. dichotoma and L. procera showed an increase. Xylem nitrate decreased in L. procera and B. dichotoma in the dry and wet seasons, respectively, and ammonium increased only in V. japurensis and V. cayennensis in the wet. Xylem arginine increased in all plant species after a period of pasture abandonment (except B. dichotoma). Tree species growing in pasture abandoned areas didn’t show the same pattern of use of nitrogen, and this can be important in order to understand the nitrogen metabolism of trees in the Amazon region during forest restoration.

Características adaptativas da associação simbiótica e da fixação biológica do nitrogênio molecular em plantas jovens de Lonchocarpus muehlbergianus Hassl., uma leguminosa arbórea nativa do Cerrado

O nitrogênio mineral afeta negativamente a simbiose e a fixação biológica do nitrogênio em plantas cultivadas. Entretanto, este efeito não é verificado em algumas espécies arbóreas, pouco estudadas até o momento. O objetivo deste trabalho foi avaliar a capacidade de Lonchocarpus muehlbergianus, espécie arbórea nativa do Cerrado, em utilizar o nitrogênio molecular, na presença do nitrogênio mineral (nitrato), característica desejável para plantas fixadoras crescendo em solos com nitrato como principal forma de nitrogênio disponível. Foram determinados o número e a massa seca dos nódulos, da parte aérea e das raízes, bem como o conteúdo de nitrato, aminoácidos e ureídeos, transportados pelo xilema e a atividade da redutase do nitrato. Foi observado que o número e a massa seca dos nódulos não foram negativamente afetados pelo nitrato. Ocorreu pequeno aumento na massa seca da parte aérea e do sistema radicular de plantas noduladas tratadas com nitrato, resultado verificado também para os teores de aminoácidos, ureídeos e atividade da redutase do nitrato. Os resultados obtidos sugerem que a espécie tem capacidade de utilizar tanto nitrogênio mineral quanto molecular, uma vez que o transporte de ureídeos, do sistema radicular para a parte aérea, não foi reduzido em plantas noduladas tratadas com nitrato.

Increased nitrogen‐use efficiency in transgenic rice plants over‐expressing a nitrogen‐responsive early nodulin gene identified from rice expression profiling

Development of genetic varieties with improved nitrogen-use efficiency (NUE) is essential for sustainable agriculture. In this study, we developed a growth system for rice wherein N was the growth-limiting factor, and identified N-responsive genes by a whole genome transcriptional profiling approach. Some genes were selected to test their functionality in NUE by a transgenic approach. One such example with positive effects on NUE is an early nodulin gene OsENOD93-1. This OsENOD93-1 gene responded significantly to both N induction and N reduction. Transgenic rice plants over-expressing the OsENOD93-1 gene had increased shoot dry biomass and seed yield. This OsENOD93-1 gene was expressed at high levels in roots of wild-type (WT) plants, and its protein product was localized in mitochondria. Transgenic plants accumulated higher concentrations of total amino acids and total N in roots. A higher concentration of amino acids in xylem sap was detected in transgenic plants, especially under N stress. In situ hybridization revealed that OsENOD93-1 is expressed in vascular bundles, as well as in epidermis and endodermis. This work demonstrates that transcriptional profiling, coupled with a transgenic validation approach, is an effective strategy for gene discovery. The knowledge gained from this study could be applied to other important crops.

The Role of Amino Acids in the Long-Distance Transport of La and Y in the Xylem Sap of Tomato

This study focuses on the role of amino acids in xylem sap of tomato grown in hydroponics in a medium supplemented with a series of concentration of La and Y. Eighteen amino acids in xylem saps were identified and measured by reversed-phase high-performance liquid chromatography. The main amino acids in xylem sap samples of the tomato are histidine, tryptophan, aspartic acid, and glutamic acid. The concentration of glutamic acid in xylem sap significantly increased in the La and Y treatment compared to the control. By analyzing the correlation between concentrations of amino acids and concentrations of La and Y in the xylem saps, we considered that the glutamic acid in xylem saps seemed to participate in the long-distance La and Y translocation processes, and histidine did not relate to xylem La and Y transport of tomato. The role of other amino acids which was excreted by tomato has not been demonstrated in the long-distance transport of La and Y in the xylem.

Transport of Nitrogen Assimilation in Xylem Vessels of Green Tea Plants Fed with NH 4-N and NO 3-N

An experiment was carried out to study the transport process of nitrogen (N) assimilation from tea roots by monitoring the dynamic composition of N compounds in xylem sap after 15N-NO 3 and 15N-NH 4 were fed to the root of tea plants ( Camellia sinensis L.). Results showed that the main amino acids were glutamine, theanine, arginine, asparic acid and glutamic acid, which accounted for 49%, 17%, 8%, 7%, and 4%, respectively, of the total amino acids in the xylem sap. After the tea plants were fed with 15N-NO 3 and 15N-NH 4 for 48 h, the amount of total amino acids in xylem sap significantly increased and those fed with 15N-NH 4 had higher increment than those with 15N-NO 3. Two hours after 15N- NO 3 and 15N-NH 4 were fed, 15N abundance in glutamine, asparagine, glutamic acid, alanine, and arginine were detected and increased quickly over time. This indicated that it took less than 2 h for NO 3-N and NH 4-N to be absorbed by tea roots, incorporated into the above amino acids and transported to the xylem sap. Rapid increase in 15N-NO 3 in the xylem sap of tea plants fed with 15N-NO 3 indicated that nitrate could be directly transported to the xylem sap. Glutamine, theanine, and alanine were the main amino acids transported in xylem sap of tea plants fed with both 15N-NO 3 and 15N-NH 4.

Does legume nitrogen fixation underpin host quality for the hemiparasitic plant Rhinanthus minor?

The high quality of leguminous hosts for the parasitic plant Rhinanthus minor (in terms of growth and fecundity), compared with forbs (non-leguminous dicots) has long been assumed to be a function of the legume's ability to fix atmospheric nitrogen (N) from the air and the potential for direct transfer of compatible amino compounds to the parasite. Using associations between Rhinanthus minor and Vicia faba (Fabaceae) that receive N either exclusively via symbiotic associations with rhizobia supplying organic N fixed from N(2) or exclusively through the supply of inorganic nitrate to the substrate, the underlying reasons for the quality of legumes as hosts for this parasite are unravelled. It is shown that sole dependence of the host, V. faba, on N fixation results in lower growth of the attached parasite than when the host is grown in a substrate supplied exclusively with inorganic N. In contrast, the host plants themselves achieved a similar biomass irrespective of their N source. The physiological basis for this is investigated in terms of N and abscisic acid (ABA) partitioning, haustorial penetration, and xylem sap amino acid profiles. It is concluded that legume N fixation does not underpin the quality of legumes as hosts for Rhinanthus but rather the well-developed haustorium formed by the parasite, coupled with the lack of defensive response of the host tissues to the invading haustorium and the presence of sufficient nitrogenous compounds in the xylem sap accessible to the parasite haustoria, would appear to be the primary factors influencing host quality of the legumes.

Changes in the Composition of Xylem Sap during Development of the Spadix of Skunk Cabbage (Symplocarpus foetidus)

The spadix of skunk cabbage, Symplocarpus foetidus, is thermogenic and maintains an internal temperature of around 20 degrees C even when the ambient air temperature drops below freezing. This homeothermic heat production is observed only during the stigma stage, and thereafter ceases at the male stage when pollen is shed. To clarify the regulatory mechanism by which the stigma stage-specific heat production occurs in the spadix, sugars, organic acids, and amino acids in xylem sap were analyzed and compared with those of post-thermogenic plants. Interestingly, no significant difference was observed in the total volume of xylem sap per fresh weight of the spadix between thermogenic (31.2+/-24.7 microl h(-1) g(-1)) and post-thermogenic (50.5+/-30.4 microl h(-1) g(-1)) plants. However, concentrations of sugars (sucrose, glucose, and fructose), organic acids (malate and succinate), and amino acids (Asp, Asn, Glu, Gln, Gly, and Ala) in xylem sap decreased remarkably in post-thermogenic plants. Our results indicate that the composition of the xylem sap differs during the development of the spadix of S. foetidus.

Amino acid export from infected cells ofVicia fabaroot nodules: Evidence for an apoplastic step in the infected zone

In root nodules of leguminous plants, such asVicia fabaL., N2is fixed by rhizobial bacteroids within infected cells. These cells are located in the centre of the nodule, whereas the vascular system serving import and export of solutes is located in the periphery. Within the infected central tissue, metabolites may travel symplastically by using bands of interconnected uninfected cells. Structural evidence, however, speaks against symplastic movement between infected cells themselves. The present work examined the possibility of an apoplastic step in amino acid export from infected cells. Incubation experiments with dissected central tissue demonstrated the release of amino compounds by infected cells. The predominant compound released was asparagine, which is also the major amino acid in xylem sap of legumes forming indeterminate nodules. During incubation of central infected tissue, medium acidification by plasma membrane H+‐ATPase quickly turned into slight alkalization, probably caused by the released amino acids. In vivo, this process would lead to an increased apoplastic pH with consequences for processes relying on the proton gradient across the plasma membrane. Uptake of14C‐labelled amino acids by uninfected and infected cells was studied using protoplasts isolated from the central nodule tissue. Uninfected protoplasts accumulated amino acids with low specificity in a ΔpH‐dependent, bi‐phasic manner, whereas infected protoplasts did not absorb amino acids from the medium. This indicates that uninfected protoplasts not only function in metabolite transport, but also in collection of amino acids from the apoplast. Taken together, both experimental approaches demonstrate the possibility of an apoplastic export step for amino acids in the central tissue of indeterminate legume nodules.

Ureide and amino acids in xylem sap of soybean (Glycine max L.) are affected by both nodulation and nitrogen supply from soil

To estimate the effect of nitrogen fixation on the nitrogen metabolism of soybean, changes in the concentrations of nitrogenous compounds in the xylem sap from nodulated plants of soybean (Glycine max. L. cv. T202) were compared with those from the non-nodulated isoline (T201) grown in fields. Although changes in the concentrations of 16 out of 19 amino acids in the xylem sap from non-nodulated plants were correlated with those of ureides, none of them in the xylem sap from nodulated plants showed any significant correlation with ureides. On the other hand, for some of the amino acids from the nodulated plants, the changes in the concentrations showed significant correlations with each other, in the same way as those of the non-nodulated plants. These results suggested that nitrogen fixation affects differently on the concentrations of the various nitrogenous compounds in the xylem sap and that it is possible to discriminate between ureides derived from N2 fixation and those derived from other sources.

Measurement of xylem sap amino acid concentrations in conjunction with whole tree transpiration estimates spring N remobilization by cherry (Prunus avium L.) trees

Abstract Prunus avium trees were grown in sand culture for one vegetative season with contrasting N supplies, in order to precondition their N storage capacities. During the spring of the second year a constant amount of 15N was supplied to all the trees, and the recovery of unlabelled N in the new biomass production was used as a direct measure of N remobilization. Destructive harvests were taken during spring to determine the pattern of N remobilization and uptake. Measurements of both xylem sap amino acid profiles and whole tree transpiration rates were taken, to determine whether specific amino acids are translocated as a consequence of N remobilization and if remobilization can be quantified by calculating the flux of these amino acids in the xylem. Whereas remobilization started immediately after bud burst, N derived from uptake by root appeared in the leaves only 3 weeks later. The tree internal N status affected both the amount of N remobilization and its dynamics. The concentration of xylem sap amino acids peaked shortly after bud burst, concurrently with the period of fastest remobilization. Few amino acids and amides (Gln, Asn and Asp) were responsible for most of N translocated through the xylem; however, their relative concentration varied over spring, demonstrating that the transport of remobilized N occurred mainly with Gln whereas transport of N taken up from roots occurred mainly with Asn. Coupling measurements of amino acid N in the xylem sap with transpiration values was well correlated with the recovery of unlabelled N in the new biomass production. These results are discussed in relation to the possibility of measuring the spring remobilization of N in field‐grown trees by calculating the flux of N translocation in the xylem.

Metabolismo do nitrogênio em alfafa nodulada sob supressão e ressuprimento de fósforo

Estudaram-se os efeitos da supressão e do ressuprimento de Pi sobre o metabolismo do nitrogênio, mediante a fixação biológica do nitrogênio atmosférico (N2) e atividade da GS, Fd-GOGAT e NADH-GOGAT, em plantas de alfafa, cv. Flórida 77, inoculadas com Sinorhizobium meliloti, em diferentes estádios do desenvolvimento vegetativo (V3 e V4) e reprodutivo (R6 e R8). O ensaio foi conduzido em casa-de-vegetação e as plantas cultivadas em solução nutritiva. O período de supressão de Pi por dez dias reduziu os teores de Pi nas folhas e nos nódulos em todos os estádios do desenvolvimento, ao passo que nas raízes essa redução somente foi observada nos estádios vegetativos. Após o ressuprimento de Pi por igual período, ou seja, dez dias, foi observada a recuperação nos estádios R6 e R8 para folhas, V3 e V4 para raízes e V3 para os nódulos. A supressão de Pi reduziu significativamente os teores de aminoácidos totais nas folhas e nas raízes em todos os estádios do desenvolvimento, indicando que houve alteração no processo de fixação do N2. Após o ressuprimento, os teores de aminoácidos totais nas raízes, em todos os estádios do desenvolvimento, alcançaram valores similares àqueles das plantas do tratamento-controle, ao passo que nas folhas isso só ocorreu nos estádios vegetativos. A composição de aminoácidos na seiva do xilema não foi alterada em função da supressão e do ressuprimento de Pi. As atividades da GS e Fd-GOGAT, nos nódulos, foram reduzidas apenas nos estádios V3 e R8, enquanto com o ressuprimento não houve recuperação da Fd-GOGAT. Contudo, houve a recuperação da atividade da GS em R8. Nas folhas, a atividade da GS foi significativamente alterada em todos os estádios, enquanto a da Fd-GOGAT foi alterada somente em V3 e V4. Após o ressuprimento, não houve a recuperação da atividade da GS e Fd-GOGAT em V3. A NADH-GOGAT nas folhas e nos nódulos foi significativamente reduzida nos tratamentos de supressão de Pi em todos os estádios avaliados, não havendo recuperação após o ressuprimento. A NADH-GOGAT foi muito sensível à baixa disponibilidade de Pi. A supressão do Pi parece exercer controle na atividade dessas enzimas durante os diferentes estádios do desenvolvimento.

Simultaneous collection of xylem sap from Rhinanthus minor and the hosts Hordeum and Trifolium: hydraulic properties, xylem sap composition and effects of attachment

The facultative hemiparasite Rhinanthus minor was grown alone, or with either Hordeum vulgare or Trifolium alpestre as a host. All plants were fed 5 mM nitrate. In the parasites, successful attachment led to dramatic increases in growth (particularly with barley as host) and in tissue concentrations of total N, NO3−, H2PO4− and K+, as well as moderate increases in Cl− and SO42−. Mg2+ and Ca2+ concentrations either remained unchanged, increased or decreased, depending on the host. Xylem sap was collected from leaf veins (barley) or the stem (Rhinanthus and clover), by applying pneumatic pressure to the rooted soil to raise the soil water potential so that in vivo xylem sap exuded from small incisions once the applied pressure balanced the tension exerted by transpiration. High balancing pressures were needed for unattached Rhinanthus, whereas simultaneous collection of xylem sap from attached Rhinanthus and its host, at a much lower balancing pressure, was possible only when the parasite was enclosed in polyethylene film and high transpiration abolished. From plots of xylem sap volume flow versus applied pressure, the hydraulic conductivity Lp and the overall hydraulic resistance r were obtained. The value of r was high in unattached Rhinanthus and dramatically decreased by attachment to a host, highlighting the improved access to water gained by Rhinanthus when parasitizing a host. For the parasites, attachment resulted in greatly increased concentrations and solute flow rates in xylem of K+, NO3−, H2PO4− and amino acids, and decreased concentrations of Ca2+ and Mg2+. Estimates of NO3− reduction in the parasite showed that 99% was reduced in unattached plants, 85% in those attached to clover and 52% in those attached to barley. In the parasitized hosts, ion concentrations in xylem sap were somewhat increased relative to unparasitized controls. Conversely, xylem sap amino‐acid concentrations in infected hosts were decreased. Glutamine (Gln) was the principal amino acid in xylem sap of unattached Rhinanthus, but after attachment to both hosts asparagine (Asn) predominated. In clover, Asn was the major transport amino acid, suggesting massive transfer of Asn from host to parasite. In unparasitized barley, however, Gln was the major xylem sap amino acid, but unexpectedly, in this species Asn was induced as the principal amino acid when parasitized. The results are discussed in terms of mutual host–parasite interactions.

The main amino acids in xylem sap of <em>Vitis vinifera</em> L. var. Cabernet Franc during the vegetative cycle. Search for an amino acid marker

<p style="text-align: justify;">Numerous studies have been carried out on the vine, must and wine, but few on sap. Main phenological stages i.e. bud burst, the flowering period, veraison and the ripening period have been well described. However, at the present time, no study is available identifying the main amino acids of the xylem sap, at the formentioned periods. Located within the « Graves de Pessac-Léognan » vineyard, the plot area studied has a clayey-chalky soil with a small amount of sand present. The cultivar Cabernet franc was grafted on the Fercal rootstock. Planted in June 1982, the vine was trained with Guyot pruning and no tillage. The density of the plantation was 5.550 vines per ha. Four rows of 21 vines were sampled.</p><p style="text-align: justify;">Analysis of xylem sap, by H.P.L.C., at the four stages, taken from several vintages, showed that the global content of amino acids varied year to year (LARCHEVÊQUE, 1998). The experiment reported on herein was carried out in order to determine both the main amino acids in the xylem sap and to identify a marker amongst them, having the same evolution as that of the global amino acid content from one phenological stage to the next. A pool of eight amino acids, all present in large quantities (about 80 p. cent of total amino acid content), was always noted : asparagine/glutamine, tyrosine, arginine, aspartic acid, glutamic acid, histidine and proline. Concentration levels of these components differed in sap, depending on the vintage, at the same phenological stage. At bud burst, as at the flowering period, the sap had a similar qualitative composition.</p><p style="text-align: justify;">It was noteworthy that aspartic acid evidenced the same evolution that of the total amino acid content (i.e. the same variation in percentage) from one phenological stage to the next. Aspartic acid should therefore be regarded as a « marker » of total amino acid content evolution during the vegetative cycle.</p>

Xylem Transfer of Organic Solutes inSantalum albumL. (Indian Sandalwood) in Association with Legume and Non-legume Hosts

Indian sandalwood (Santalum album), a commercially important root hemi-parasitic angiosperm, was partnered singly in pot culture with one of three nitrogen-fixing legumes or a eucalypt host. Xylem (tracheal) sap of stems of host and parasite and ethanolic extracts of endophytic tissue of haustoria of the parasite were analysed for amino acids, organic acids and sugars to determine which sets of solutes were available to and obtained by the parasite from different hosts. There were high concentrations of asparagine, followed by glutamate, aspartate and γ-amino butyrate in the xylem sap solutes of the three legume hosts (Sesbania formosa, Acacia trachycarpa and A. ampliceps) and much higher levels of glutamate, aspartate, glutamine and arginine in the non-legume, Eucalyptus camaldulensis. Close resemblances between Santalum and legume hosts in concentration and composition of xylem sap amino acids, and in the amino acid spectra of the corresponding parasite endophytic tissue, indicated substantial direct intake of xylem N by Santalum from these hosts. By contrast, low N levels in xylem sap of E. camaldulensis and dissimilarities between its amino acid composition and that of partnered Santalum indicated that the parasite obtained little N from the xylem sap of this host. Xylem sap of hosts contained variable amounts of sucrose. glucose and fructose, whereas that of matching parasites was dominated by fructose. Dissimilarities were also evident in the proportional amounts of xylem-borne organic acids between hosts and parasite particularly for the eucalypt: Santalum partnership. Leaf extracts of the host: parasite pairings generally showed substantial differences in sugar and organic acid balance between partner species. Similarly, where amino acid spectra of host and parasite xylem sap and corresponding haustorial endophytes were closely similar, respective leaf compositions were markedly dissimilar. This implied that substantial metabolic patterns of incoming xylem solutes were highly idiosyncratic of the species in question. Data are related to previous information showing superior growth performance and higher photosynthetic rates and foliar N concentrations in Santalum partnered with the three legumes than with the eucalypt.

Amino acid content in xylem sap of regrowing alfalfa (Medicago sativa L.): Relations with N uptake, N2 fixation and N remobilization

During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N2 and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N2 fixation and endogenous N remobilization were estimated by 15N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N2 or from NH4NO3 during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N2 fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH4NO3 grown and in N2 fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine.

Effects of applied nitrogen upon aspects of nitrogen metabolism and transport in developing nodulated winged bean plants

Nodulated winged bean [Psophocarpus tetragonolobus (L.) DC., cv. UPS 122] were grown under constant environmental conditions and supplied with mineral nutrient solution in which nitrogen was absent or was present as nitrate (12 mg N week‐1 plant‐1).Nitrate treatment dramatically promoted plant growth, increased fruit weight 1.6 fold, was necessary for tuberisation and enhanced nodulation. The in vitro accumulation of 14C into asparagine and aspartate components of excised nodules supplied with exogenous 14CO2 and [14C]‐D‐glucose was greater for nitrate‐treated plants, whilst accumulation into ureides was reduced by nitrate treatment. Levels of amino acids in xylem sap were greater for plants supplied with a complete nutrient solution, than those grown without applied nitrate, particularly for asparagine, glutamine and proline. Xylem ureide levels were greater for plants grown in the absence of supplementary nitrate.Nitrogen accumulated in leaf, stem and petiole, and root nodule tissues for utilisation during fruit development; peak nitrogen levels and time of anthesis were retarded for plants grown without applied nitrate. The shoot ureide content increased during fruiting, coincident with decreases in the total nitrogen content, indicating that ureide pools are not utilised during the early reproductive phase. However ureide reserves, particularly allantoin, were utilised during the later stages of pod fill.Enzyme activity which metabolised asparagine was found throughout the plant and was identified as K+‐dependent asparaginase (EC 3.5.1.1) and an aminotransferase. Apart from temporal differences in developmental profiles of enzyme activity, the activity of these enzymes and of allantoinase (EC 3.5.2.5) in developing tissues were similar for both treatments. The main differences were greater asparaginase and asparagine:pyruvate aminotransferase activities in root tissues and fruit of nitrate‐supplied plants; allantoinase activity in the primary roots of plants grown without nitrate decreased during development, whilst activity in developing tubers (nitrate‐supplied plants) increased.

Adaptation d'une méthode d'analyse des acides aminés, par chromatographie liquide haute performance, dans les sèves xylémiques

Modified procedure for the high-performance liquid chromatographic analysis of amino acids in xylem sap. Pre-column o-phthaldialdehyde derivatization followed by high-performance liquid chromatography was used for the determination of amino acids in xylem sap. The pre-column derivatization conditions have been reviewed. To reduce analysis time and to improve peak separation, the solvent composition and the gradient programme were modified. The amino acids of tomato xylem sap were identified using α-aminobutyric acid as internal standard. The reproducibility of this new method was tested and its field of application is discussed.

Identification of a new, naturally occurring, non proteic amino acid in xylem sap of pisum sativum

The xylem sap of nitrogen-fixing Pisum Sativum cv Homesteader has been examined by capillary gas chromatography and by gas chromatography mass spectrometry in both electron-impact and chemical ionization modes following the formation of N-heptafluorobutyryl isobutyl ester derivatives. One of the compounds thus detected had a mass of 389 and contained chlorine, one carboxylic acid group and a nitrogen atom. High-resolution mass spectrometry indicated that there were no other hetero atoms present in the molecule. The composition was determined to be C4H8NO2Cl. This composition can be explained only in terms of a chloroamino butyric acid.

Effects of Vesicular-arbuscular Mycorrhizae and Nitrogen Source on Growth and Transport Amino Acid Composition of Pittosporum tobira

Abstract Pittosporum tobira plants were inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae or provided with an inoculum filtrate (nonVAM) and fertilized with 1 of 5 NH4+/NO3− ratios. Colonized plants had more branching, greater fresh weight, and higher visual grades than nonVAM plants, especially when grown at 50%–75% NO3−-N. Colonized plants also had higher concentrations of transport amino acids in xylem sap compared to nonVAM plants. Results suggest that colonization by Glomus mosseae may affect N metabolism in P. tobira.