Genotypic lipoxygenase variation in soybean seeds and response to nitrogen nutrition

Decreasing the lipoxygenase content of soybean (Glycine max (L.) Merr.) seed is a prerequisite for its increased use in human foods. These investigations aim to analyse the variation of lipoxygenase contents in relation to the genotype or the nitrogen nutrition of the plant. Four genotypes from a divergent selection for N 2 fixation and the recurrent parent, Weber, were grown in pots, and two Bradyrhizobium japonicum strains (G.49 and SMGS1) were used. Dinitrogen fixation was estimated in situ using the acetylene-reduction assay. The lipoxygenase activity was determined polarographically on seeds taken from plants grown under controlled conditions in the presence or absence of symbiotic N 2 fixation. The large genotypic variation observed for the lipoxygenase contents was enhanced by high N 2 fixation. The variation range of lipoxygenase contents, which was obtained through the combination of the genotypic variation and the N 2 fixation activity, was relatively large with a ratio of 2 on a seed dry-weight basis and a ratio of 2.6 when the total proteins were considered. Decreased lipoxygenase content and increased total protein content can thus be considered in parallel in a genetic context, together with more efficient N 2 fixation.