Lipoxygenase in soybean seedlings catalyzes the oxygenation of phospholipid and such activity changes after treatment with fungal elicitor

Lipoxygenase (LOX) activities in the crude extracts of soybean cotyledons on phospholipid were measured by a chemiluminescence (CL) assay system. The activity of LOX on phospholipid increased at 6 h after treatment with fungal elicitor, whereas the activity in the control experiment without elicitor treatment declined with incubation. A rise of LOX activity at 6 h incubation is considered to be induced by the elicitor treatment. The LOX fraction obtained from soybean cotyledons at 6 h after elicitation by a DEAE column chromatography was reacted with 1-palmitoyl-2-linoleoyl-phosphatidylcholine substrate. The reaction product was analyzed by HPLC equipped in series with a UV (205 nm) and a CL detector. Most of the substrate was converted to a hydroperoxy compound. By the CL-HPLC analysis after transesterification of reaction product and by mass spectrum of the trimethylsilyl derivative after reduction of methyl ester confirmed that the linoleic moiety was subjected to oxygenation at 13-position. The steric analysis of menthoxyacetyl derivative prepared from hydroxy fatty acid methyl ester showed S configuration. These findings suggest that the oxygenation of membrane lipids in biological plant tissues might be initiated by the direct action of LOX.