Short‐term resistance that persists: Rapidly induced silicon anti‐herbivore defence affects carbon‐based plant defences

Abstract

Abstract Silicon (Si) is known to alleviate diverse biotic and abiotic stresses including insect herbivory. Si accumulation in plants, notably the Poaceae, can be induced through stimulation of the jasmonic acid (JA) pathway (associated with chewing herbivores). Nevertheless, the temporal dynamics of Si accumulation as a defence response and its consequential effects on carbon‐based defences (e.g. phenolics), particularly in the short‐term, remain unclear. The model grass Brachypodium distachyon was grown in a hydroponic solution where half the plants were supplemented with 2 mM potassium silicate and half had no Si supplied. Plants were treated with methyl jasmonate (MeJA) as a form of standardised simulated herbivory. We measured Si accumulation, the phytohormones JA and salicylic acid (SA) and carbon‐based defences over 24 hr to determine the temporal dynamics of Si accumulation and the interplay between Si, simulated herbivory and plant defence machinery. MeJA‐induced Si accumulation occurred as early as 6 hr after treatment via increased JA concentrations. Si supplementation decreased SA concentrations, which could have implications on additional downstream defences. We show a trade‐off between Si and phenolics in untreated plants, but this relationship was weakened upon MeJA treatment. Further, this trade‐off did not apply to the phenolic precursor compound, phenylalanine. We provide evidence for rapidly induced Si accumulation associated with herbivory, and that increased Si accumulation impacts on phytohormones and carbon‐based defences over a 24‐hr period. Additionally, herbivory modifies the relationship between Si‐ and carbon‐based defences. Thus, in addition to its well‐documented role as a long‐term defence against herbivores, we demonstrate that, over short‐term temporal scales, Si accumulation responds to herbivore signals and impacts on plant defence machinery. A free Plain Language Summary can be found within the Supporting Information of this article.