Lipoxygenase-induced defense of soybean varieties to the attack of the velvetbean caterpillar (Anticarsia gemmatalis Hübner)

The genetic elimination of lipoxygenase isozymes (LOX) and the Kunitz trypsin inhibitor (KTI) from soybean seeds is a way to overcome the problems associated with the undesirable beany flavor of soybean products. Although the role of the lipoxygenases in higher plants has not yet been established conclusively, several studies have indicated the physiological relevance of the lipoxygenase pathway induction in plants under biotic and abiotic stress conditions. To elucidate the effect of seed lipoxygenase and KTI elimination on soybean defense against injury, a biochemical assessment of the lipoxygenase pathway in soybean leaves subjected to the attack of Anticarsia gemmatalis (Lepdoptera:Noctuidae) was carried out in a commercial cultivar and three lines derived from this cultivar, which differ on the presence and absence of LOX and the protease inhibitor KTI. The soybean plants responded to the attack of the insect via the LOX pathway, by increasing LOX activity and protease inhibition in their leaves. Since jasmonic acid seems to activate transcription of genes encoding for protease inhibitors, the soybean plant responded to the injury via the LOX pathway, preferentially producing jasmonate and protease inhibitors. There was no association between the lack of LOX and KTI from the seeds and the leaf defense against injury, indicating that the loss of the genes for both proteins from soybean seeds does not interfere with the plant ability to respond to the attack of A. gemmatalis via this pathway.