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.

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Aspergillus oryzae and Rhizopus oryzae were compared for inducing the production of prenylated stilbenoids in peanut seedlings. The fungus was applied at two different time points: directly after soaking (day 1) or after 2 days of germination (day 3). Aspergillus- and Rhizopus-elicited peanut seedlings accumulated an array of prenylated stilbenoids, with overlap in compounds induced, but also with compounds specific to the fungal treatment. The differences were confirmed to be due to modification of prenylated stilbenoids by the fungus itself. Each fungus appeared to deploy different strategies for modification. The content of prenylated stilbenoids modified by fungi accounted for around 8% to 49% (w/w) of total stilbenoids. The contents of modified prenylated stilbenoids were higher when the fungus was applied on day 1 instead of day 3. Altogether, type of fungus and time point of inoculation appeared to be crucial parameters for optimizing accumulation of prenylated stilbenoids in peanut seedlings.