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ARS Home » Research » Publications at this Location » Publication #111917
Title: LEAF UREIDE DEGRADATION AND N2 FIXATION TOLERANCE TO WATER DEFICIT IN SOYBEAN.

Author
item VADEZ, VINCENT - UNIVERSITY OF FLORIDA
item Sinclair, Thomas

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Problem: One of the large benefits of soybean production is that the crop is able to undertake symbiotic nitrogen fixation so that no commercial nitrogen fertilizer needs to be added to the crop. However, nitrogen fixation is very sensitive to soil drying so that even modest soil drying may result in a loss of activity and decreased crop yield. The source of this sensitivity is associated with the accumulation of nitrogen fixation products in the plant. Accomplishment: Recently, it was confirmed that two pathways exist in soybean to breakdown these products of nitrogen fixation. The research reported in this paper was done in cooperation with an ARS-USDA scientist located at Gainesville, FL to determine if there was an association between breakdown pathway and sensitivity of nitrogen fixation to soil drying. A difference was, in fact, demonstrated with one pathway tending to be associated with greater drought tolerance in its nitrogen fixation. Usefulness: These results are encouraging for developing soybean cultivars with a breakdown pathway that lessens the loss of nitrogen fixation activity as soils dry.

Technical Abstract: Accumulation of ureides in leaves has been shown to be associated with N2 fixation sensitivity in soybean to soil water deficit. Consequently, ureide degradation in leaves may be a key to increasing soybean tolerance to dry soils. Previous research showed that allantoic acid degradation is catalyzed by different enzymes in cultivars Maple Arrow and Williams. The enzyme found in Williams requires manganese as a cofactor. The first objective of this study was to determine if the two degradation pathways were associated with differences in N2 sensitivity to soil water deficits. N2 fixation of Williams grown on low-Mn soil was sensitive to stress but it was relatively tolerant when grown on soil amended with Mn. N2 fixation in Maple Arrow was relatively tolerant of soil drying regardless of the Mn treatment. The second objective of this study was to expand the study of the degradation pathway to nine additional genotypes. Based on ureide degradation in the presence and absence of Mn, these genotypes also segregated for the two degradation pathways. Those genotypes with the Mn-dependent pathway had drought-sensitive N2 fixation with one exception. The genotypes not requiring Mn for ureide degradation were drought tolerant except for one genotype.