Amino acid and ureide transport in the xylem of symbiotic soybean plants during short-term flooding of the root system in the presence of different sources of nitrogen

Abstract

The transport of organic N compounds to the shoot in the xylem sap of nodulated soybean plants was investigated in an attempt to better understand the changes in N metabolism under root hypoxia (first 5 days of flooding), with different sources of N in the medium. NO 3 -is beneficial for tolerance of plants to waterlogging, whereas other N sources such as NH 4 + and NH 4 NO 3, are not. Nevertheless, in the presence of NH 4 + high levels of amino acids were transported in the xylem, consistent with its assimilation. Some increase in the transport of amino acids was also seen with NO 3 -nutrition during waterlogging, but not with N-free medium. Ureide transport in the xylem was severely reduced during waterlogging, consistent with impaired N 2 fixation under these conditions. The relative proportions of some amino acids in the xylem showed dramatic changes during treatment. Alanine increased tremendously under root hypoxia, especially with NH 4 + as N source, where it reached near 70 % of the total amino acids present. Aspartic acid, on the other hand, dropped to very low levels and was inversely related to alanine levels, consistent with this amino acid being the immediate source of N for alanine synthesis. Glutamine levels also fell to a larger or lesser extent, depending on the N source present. The changes in asparagine, one of the prominent amino acids of the xylem sap, were most outstanding in the treatment with NO 3 -, where they showed a large increase, characteristic of plants switching from dependence on N 2 fixation to NO 3 -assimilation. The data indicate that the lesser effectiveness of NH 4 + during waterlogging, in contrast to NO 3 -, involves restricted amino acids metabolism, and may result from energy metabolism being directed towards NH 4 + detoxification. Key words: Glycine max, alanine, hypoxia, N metabolism.Transporte de aminoácidos e ureídeos no xilema de plantas de soja simbióticas sob curto período de alagamento do sistema radicular com diferentes fontes de nitrogênio: O transporte de compostos nitrogenados orgânicos à parte aérea de plantas de soja, através da seiva do xilema, foi investigado para melhor entender as mudanças no metabolismo do sistema radicular sob hipoxia (primeiros 5 dias de alagamento) e com diferentes fontes de N no meio. O NO 3 -é benéfico à tolerância das plantas ao alagamento, enquanto que outras fontes de N, como o NH 4 NO 3 e o NH 4 , não são. Contudo, na presença de NH 4 + elevados níveis de aminoácidos foram transportados no xilema, demonstrando sua assimilação. Algum aumento no transporte de aminoácidos também ocorreu com a presença de NO 3 -durante o alagamento, mas não na ausência de N no meio. O transporte de ureídeos no xilema foi severamente reduzido durante o alagamento, demonstrando a inibição da fixação de N 2 nessa condição. As proporções relativas de alguns aminoácidos no xilema demonstraram mudanças drásticas durante os tratamentos. Alanina aumentou acentuadamente com o sistema radicular sob hipoxia, especialmente com NH 4 + como fonte de N, quando e...

Effect of salt on the growth and metabolism of Glycine max

“…The present data show a reduction in this amino acid under salt treatment. Puiatti and Sodek (1999), Souza and Sodek (2003) and Thomas and Sodek (2006) observed a reduction in the abundance of Asn in the xylem sap of soybean plants cultivated with nitrate and subjected to hypoxia and discussed the possibility that the reduction might involve conversion of this amino acid (or its precursor, Asp) to Ala (see Fig. 1).…”

Metabolismo do nitrogênio no sistema radicular de leguminosas em condição de hipoxia

“…In the absence of any external nitrogen supply, the amount of alanine increased during waterlogging by a factor of 11, rising from 0.60 to 6.85 nmol waterlogging. These data can explain a similar relationship between N source and Ala production found by Thomas and Sodek (2006) with respect to xylem sap Ala transport in soybean plants during waterlogging. Independent of the nitrogen treatment, the level of the GmAlaAT1 transcript in both roots and nodules showed a strong increase during hypoxia (Fig 7 C).…”

Herbivorous insect decreases plant nutrient uptake: the role of soil nutrient availability and association of below‐ground symbionts

“…Soybean xylem sap contains three forms of nitrogen: ureides (allantoin and allantoic acid), amino acids (mainly asparagine and glutamine), and nitrate (Matsumoto et al , ). Nitrogen derived from rhizobia is transformed into ureides in root nodules, and is transported through xylem vessels (Streeter, ), whereas nitrogen absorbed from the soil is mainly transported in the form of nitrate and amino acids (Thomas & Sodek, ).…”