Modulation of Isoflavonoid Composition of Rhizopus oryzae Elicited Soybean (Glycine max) Seedlings by Light and Wounding

The isoflavonoid profile of soybean was altered in different ways by stimulation of defense response upon germination. The combination of simultaneous germination and induction by Rhizopus oryzae increased the total isoflavonoid content of soybeans over 2-fold. Pterocarpans became the predominant isoflavonoids, up to 50% (w/w) of total isoflavonoids. To modulate both isoflavonoid content and composition further, the treatment was extended with wounding or light stimuli. The total isoflavonoid content could be increased over 3-fold compared to untreated beans by growing fungus-elicited soybean seedlings in light, whereas wounding was less effective. Interestingly, light altered the composition of prenylated pterocarpans by mediating the position of prenylation. The 2-prenylated pterocarpan level increased 2-fold, whereas that of 4-prenylated pterocarpan remained similar. Taken together, fungus was the most effective elicitor to alter the isoflavonoid content and composition of soybean seedlings, the impact of which can be further enhanced and mediated by additional stimuli, particularly light.