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

Abstract

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.

Feedback regulation of symbiotic N2 fixation under drought stress

“…Interestingly, our work showed that there was a major interaction between Mn nutrition and the decline of nitrogen fixation under water deficit [28], in agreement with the data of Purcell, King and Ball [16]. Indeed, a Mn application allowing a leaf Mn concentration of about 21 to 32 mg⋅kg -1 delayed the decline of nitrogenase activity induced by water deficit, which appeared to be linked to an increased leaf Mn availability, leading to an enhanced rate of in situ ureide degradation.…”

“…Because of Mn's role in the ureide degradation in soybean leaves, Purcell, King and Ball [16] hypothesized that Mn might regulate nitrogen fixation under water deficit. Interestingly, our work showed that there was a major interaction between Mn nutrition and the decline of nitrogen fixation under water deficit [28], in agreement with the data of Purcell, King and Ball [16].…”

Water restriction and physiological traits in soybean genotypes contrasting for nitrogen fixation drought tolerance

“…Higher accumulation of Mn in the NFDT genotype R01-581F suggests a further attribute inherited from 'Jackson'. Manganese-dependent metabolism of ureides suggests that higher levels of Mn in leaves may help soybean to cope with accumulation of ureides in shoots under drought (Purcell et al, 2000). Although Vadez and Sinclair (2002) observed the same trend, there is evidence that the enzymatic degradation of ureides in 'Jackson' may not require Mn as a cofactor.…”

“…Climate changes are expected to reduce rainfall in subtropical areas by 20 % (IPCC, 2007), increase the frequency of drought and cause losses to soybean crop yields. Studies have indicated that the combination of three mechanisms may impair the BNF under drought: (1) limitation of oxygen supply to nodules (King and Purcell, 2001); (2) shortage of carbon supply to bacteroids due to reductions in the activity of sucrose synthase (SS) (Arrese-Igor et al, 2011); and (3) regulation of N metabolism by feedback of N compounds, mainly ureides (Purcell et al, 2000;Collier and Tegeder, 2012).…”

Manganese and zinc concentrations in maize genotypes grown on soils differing in acidity

“…Mn leaf accumulation has been shown to be related to certain aspects of drought tolerance in soybean (Purcell et al, 2000;Vadez and Sinclair, 2002;Sinclair et al, 2007) and cotton (Weil et al, 1997). Very few results have been published on the relationship between Mn status and drought tolerance in maize genotypes (De et al, 2004).…”