Two soybean genotypes lacking lipoxygenase-1

The U.S. Department of Agriculture soybean germplasm collection (6,499 accessions) was screened for genotypes with greatly reduced or missing lipoxygenase-1 (L-1) [linoleate: O₂ oxidoreductase, EC 1.13.11.12] and lipoxygenase-2 and L-3 (L-2 and L-3) activity. The L-1 assay used linoleic acid dispersed in Tween-20 at pH 9.0 as the substrate (acid assay) and the L-2 and L-3 assay used linoleic acid methyl ester dispersed in ethanol at pH 7.0 as the substrate (ester assay). The spectrophotometric assay based on conjugated diene formation at 234 mm was used in the qualitative screening procedure. Two plant introductions (PI), 133226 from Indonesia and PI 408251 from Korea lacked L-1 activity. Oxygen uptake, electrophoresis and isoelectric focusing confirm the lack of detectable L-1 activity in the seed of these two genotypes. Radial diffusion against soybean seed lipoxygenase antiserum showed that the two genotypes are missing a precipitin band that normal soybean genotypes and purified lipoxygenase from soybean seed exhibit. Neither the L-1 variants nor any other accessions tested had greatly reduced activity with the ester assay.