Inhibition of N2 Fixation in Soybean Is Associated with Elevated Ureides and Amino Acids

Abstract

Decreased N 2 fixation in soybean (Glycine max) L. Merr. during water deficits has been associated with increases in ureides and free amino acids in plant tissues, indicating a potential feedback inhibition by these compounds in response to drought. We evaluated concentrations of ureides and amino acids in leaf and nodule tissue and the concurrent change in N 2 fixation in response to exogenous ureides and soil-water treatments for the cultivars Jackson and KS4895. Exogenous ureides applied to the soil and water-deficit treatments inhibited N 2 fixation by 85% to 90%. Mn fertilization increased the apparent catabolism of ureides in leaves and hastened the recovery of N 2 fixation following exogenous ureide application for both cultivars. Ureides and total free amino acids in leaves and nodules increased during water deficits and coincided with a decline in N 2 fixation for both cultivars. N 2 fixation recovered to 74% to 90% of control levels 2 d after rewatering drought-stressed plants, but leaf ureides and total nodule amino acids remained elevated in KS4895. Asparagine accounted for 82% of the increase in nodule amino acids relative to well-watered plants at 2 d after rewatering. These results indicate that leaf ureides and nodule asparagine do not feedback inhibit N 2 fixation. Compounds whose increase and decrease in concentration mirrored the decline and recovery of N 2 fixation included nodule ureides, nodule aspartate, and several amino acids in leaves, indicating that these are potential candidate molecules for feedback inhibition of N 2 fixation.Water-deficit stress is often a primary constraint of soybean (Glycine max) yields (Purcell and Specht, 2004). N 2 fixation in soybean is reportedly more sensitive to moderate water deficits than are many other plant processes including transpiration (Sall and Sinclair, 1991;Serraj and Sinclair, 1996) and leaf gas exchange (Durand et al., 1987;Djekoun and Planchon, 1991). It has been proposed that increased tolerance of N 2 fixation to water deficits would increase overall water-deficit tolerance in soybean.Despite much research effort in the area, the mechanisms influencing N 2 fixation response to limited soil water are not well understood. Accumulating evidence indicates that the decline in N 2 fixation during water deficits and genotypic differences in sensitivity to drought may be associated with levels of nitrogenous compounds, such as amino acids or ureides, in leaves or nodules of N 2 -fixing plants (Silsbury et al., 1986;Parsons et al., 1993;Oti-Boateng and Silsbury, 1993;Serraj et al., 1999a;Purcell et al., 2000;. How specific compounds regulate nodule activity is unclear, although several hypotheses have been proposed (Serraj et al., 1999b).The ureides, allantoin and allantoate, are the final products of N 2 fixation that are exported from soybean nodules to the shoot (McClure and Israel, 1979), where they are catabolized. While N 2 fixation declines in response to water deficits, shoot ureides often increase (de Silva et al., 1996; due to a decrease...

Efeito do alumínio sobre compostos nitrogenados em Urochloa spp.

“…Entretanto, esses compostos vêm sendo detectados em plantas não leguminosas e sua produção pode estar relacionada à degradação de purinas, como relatado por Todd et al (2006). Adicionalmente, o acúmulo desses compostos pode estar diretamente relacionada a aquisição de tolerância em situações estressantes, como tem sido reportado por alguns autores (SINCLAIR et al, 2003;PURCELL et al, 2004;KING;PURCELL, 2005 …”

Ureide Content of Guar under Influence of Hexaconazole and Triazophos

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Biological nitrogen fixation in soybean under water restriction and exposed to 1-methylcyclopropene

“…The effects of drought on traits related to BNF have been widely studied (King & Purcell, 2005;Hungria et al, 2006;Sinclair et al, 2007;Cerezini et al, 2014). However, despite some works on cotton, flowers, and fruits (Serek et al, 2006;De Pietro et al, 2010;Chen et al, 2015;Li et al, 2016), there is no knowledge of researches on the effect of 1-MCP on soybean, aiming to the attenuate negative effects of ethylene induced by drought stress on plant senescence, including nodules.…”

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