Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 3, 1997
Publication Date: N/A
Interpretive Summary: Plants respond to stress induced by pathogens and wounding through a variety of mechanisms. The basic work reported in this manuscript identifies a stress-induced biochemical pathway in soybeans that leads to the compound 4-hydroxynonenal (HNE). HNE is also well known in animals as an indicator of oxidative stress and has been implicated in a number of maladies. Also, HNE has been identified as a "signal" that triggers a cascade of biochemical events. This work will be useful to other scientists enabling them to pursue research related to HNE and suggests strategies to alleviate pathologies attributed to HNE in animals. The effects of HNE on plants are not yet determined, but the compound is known from previous research to inhibit fungal growth.
Technical Abstract: In previous work with soybean, Glycine max, it was reported that the initial product of 3Z-nonenal (NON) oxidation is 4-hydroperoxy-2E- nonenal (4-HPNE), and a hydroperoxide-dependent peroxygenase catalyzes the formation of 4-hydroxy-2E-nonenal. In the present work, we have attempted to purify the 4-HPNE-producing oxygenase from soybean. Chromatography on various supports had shown that oxygen uptake with NON substrate consistently coincided with lipoxygenase-1 activity. Compared with oxidation of lipoxygenase's preferred substrate, linoleic acid, the activity with NON was about 400- to 1000-fold less. Rather than obtaining the expected 4-HPNE, 4-oxo-2E-nonenal (4-ONE) was the principal product of NON oxidation, presumably arising from the enzyme-generated alkoxyl radical of 4-HPNE. In further work, a precipitous drop in activity was noted upon dilution of lipoxygenase-1 concentration; however, activity could be enhanced by spiking the reaction with 13S-hydroperoxy-9Z,11E-octadecadienoic acid. Under these conditions, the principal product of NON oxidation shifted to the expected 4-HPNE. 4-HPNE was demonstrated to be 83% of the 4S-hydroperoxy-stereoisomer. Therefore, lipoxygenase-1 is also a 3Z-alkenal oxygenase, and it exerts the same stereospecificity of oxidation as it does with polyunsaturated fatty acids. Two other lipoxygenase isozymes of soybean were also found to oxidize NON to predominately the 4S- hydroperoxy-stereoisomer.