Sensitivity of N2 Fixation Traits in Soybean Cultivar Jackson to Manganese
- Vincent Vadez and
- Thomas R. Sinclair *
There are large increases in leaf ureides, allantoin, and allantoic acid upon water deficit in N2 fixing soybean [Glycine max (L.) Merr.], which are likely to trigger a feedback inhibition of nodule activity. The degradation of ureides in the leaves appears to be a major factor associated with N2 fixation tolerance to water deficit. Since one of the possible enzymes responsible for allantoic acid degradation depends on Mn as a cofactor, we investigated the possibility that the previously demonstrated N2 fixation tolerance to water deficit of the cultivar Jackson may result from a superior ability to accumulate Mn. Indeed, Jackson was found in field and greenhouse experiments to have higher leaf Mn concentrations than other genotypes over a range of Mn availability. Acetylene reduction activity after treating Jackson plants grown on hydroponic solutions with ureide did not vary, however, with leaf Mn concentration. This was in contrast to a soybean line with N2 fixation sensitive to water deficit in which acetylene reduction activity following ureide treatment was greater as the leaf Mn concentration increased. In addition, ureide degradation rates in Jackson leaf samples with differing Mn concentrations were insensitive to Mn concentration. These results indicate that ureide degradation likely did not involve Mn as a cofactor and that ureide degradation in Jackson is catalyzed by an enzyme not requiring Mn as a cofactor. It was concluded that the capacity to maintain a high leaf Mn concentration in Jackson under sufficient Mn availability was a trait with no causal relationship to N2 fixation tolerance of water deficit.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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