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

Univ.of Arkansas, Dep. of Crop, Soil, and Environmental Sciences, 276 Altheimer Drive, Fayetteville, AR 72704 USA

View larger version (15K): [in a new window]   Fig. 1 Acetylene reduction activity (ARA) following allantoin application to roots. Relative ARA was normalized for activity prior to treatment and for rates of the control treatment on a given day. Data were averaged over foliar manganese-spray treatments (n.s.) and soybean cultivars (n.s.). The * indicates that rates differed significantly within a day between control and allantoin-treated plants, as indicated by an

View larger version (38K): [in a new window]   Fig. 2 Shoot-ureide concentration response to water-deficit treatments (A.) and manganese treatment (B.) for cultivars Jackson (J) and KS4895 (KS). Within a harvest date, different letters above bars indicate that means were significantly different, as determined by an LSD (P = 0.05). In (A.), data were averaged over cultivar and manganese treatments (water x cultivar x manganese, n.s.), and in (B.), data were averaged over water treatment

View larger version (22K): [in a new window]   Fig. 3 Petiole ureide concentration (A.) and leaf ureide concentration (B.) for Jackson and KS4895 during a drying cycle for a field experiment in 1997. Except where indicated, data were averaged over foliar manganese treatments (n.s.). Within a day, * indicates that ureide concentrations differed significantly between cultivars as determined by an F-test (P 0.05). LSD bar in panel A is for comparisons of means on Day 4

View larger version (61K): [in a new window]   Fig. 4 Model of nitrogen fixation response to manganese and ureide accumulation during water deficit. In the absence of sufficient manganese, ureide breakdown is impaired, leading to an accumulation of leaf ureides. An increase in leaf ureides results in the export of ureides from leaves to nodules, along with water and sugars carried in phloem. Increased ureide concentration in nodules inhibits N2 fixation, lessens nodule respiration and sink strength, and decreases flux of water to nodules