Beyond strengthening the leaf surface: Silicon enhances herbivore-associated plant defense responses

Upon damage, plants activate the production of toxic defense compounds that can poison or reduce the growth of insect attackers. Several studies have shown that plants supplemented with silicon (Si) have increased tolerance against both abiotic and biotic stresses including herbivores. This tolerance has been mainly associated with the accumulation of Si bodies in plant tissues, but the effect of Si on other plant resistant mechanisms has been explored only in a few systems. This research tested the effect of Si supplementation on herbivore-induced plant defenses responses.  We measured the levels of plant defensive proteins and the density of trichomes in corn, soybean and tomato plants fed by the fall armyworm (FAW) larvae Spodoptera frugiperda. Our results show that tomato plants supplemented with silicon produce a significantly greater number of glandular trichomes and had higher levels of polyphenol oxidase activity upon feeding by the FAW larvae compared with non-supplemented controls. In corn, Si-treated plants also had higher levels of trypsin inhibitor activity upon FAW feeding but the density of trichomes did not change. We conclude that Si boosts defenses upon insect herbivory in both Si-accumulators and none Si-accumulator plants. Si fertilization has the potential to be incorporated as an agricultural practice to improve plant health reducing the use of pesticides and potentially increasing yield. This research was funded by the United States Department of Agriculture (USDA), Penn State University College of Agricultural Sciences, the Entomological society of America and Monsanto Research grant.