Short‐term exposure to silicon rapidly enhances plant resistance to herbivory

Abstract

Silicon (Si) can adversely affect insect herbivores, particularly in plants that evolved the ability to accumulate large quantities of Si. Very rapid herbivore-induced accumulation of Si has recently been demonstrated, but the level of protection against herbivory this affords plants remains unknown. Brachypodium distachyon, a model Si hyperaccumulating grass, was exposed to the chewing herbivore, Helicoverpa armigera, and grown under three conditions: supplied Si over 34 days (+Si), not supplied Si (-Si), or supplied Si once herbivory began (-Si+Si). We evaluated the effectiveness of each Si treatment at reducing herbivore performance and measured Si-based defenses and phenolics (another form of defense often reduced by Si). Although Si concentrations remained lower, within 72 hr of exposure to Si, -Si+Si plants were as resistant to herbivory as +Si plants. Both +Si and -Si+Si treatments reduced herbivore damage and growth, and increased mandible wear compared to -Si. After 6 hr, herbivory increased filled Si cell density in -Si+Si plants, and within 24 hr, -Si+Si plants reached similar filled Si cell densities to +Si plants, although decreased phenolics only occurred in +Si plants. We demonstrate that plants with short-term Si exposure can rapidly accumulate Si-based anti-herbivore defenses as effectively as plants with long-term exposure.

Silica nanoparticles as pesticide against insects of different feeding types and their non-target attraction of predators

“…leafworms) but not fluid feeders (e.g. aphids) is in line with a general trend found in a meta analysis 19 . Because cheweing insects tend to elicit the jasmonic acid signaling cascade while sap feeders induce the salicylic acid pathway 77 , this suggests that chewing insects specifically activate the interaction between Si and jasmonate 19 .…”

“…aphids) is in line with a general trend found in a meta analysis 19 . Because cheweing insects tend to elicit the jasmonic acid signaling cascade while sap feeders induce the salicylic acid pathway 77 , this suggests that chewing insects specifically activate the interaction between Si and jasmonate 19 . Chewing insects also induce more groups of volatiles and in higher magnitudes than phloem feeders 77 , thereby innately tend to allow plants to attract more natural enemies than other feeding guilds.…”

“…At the base of these food chains, plants uptake silicon (Si, bulk size > 1 μm) from the soil, and their ability to do so varies according to different mechanisms of uptake 16 , 17 . Si absorbed and deposited in plant epidermal tissue (cell walls, lumen, intracellular space, and trichomes/hairs) 18 as amorphous hydrated silica (SiO 2 ·nH 2 O) can increase the rigidity of the tissue, causing increased wear to the mandibles of chewing insects 19 – 25 and modification of the mouthparts of dipteran larvae 11 , along with increased alleviation of environmental stress on plants 26 . Moreover, Si enrichment in plants biochemically defends against herbivores, by priming for jasmonate-mediated inducible defenses (with defense-related enzymes and proteins) 27 .…”

Interactions between silicon and alkaloid defences in endophyte‐infected grasses and the consequences for a folivore

“…We suggest there are at least three possible reasons why Si-rich plants had lower levels of these defences. Firstly, lower levels of damage by H. armigera feeding on Si-rich plants, as reported for Brachypodium distachyon by Waterman et al (2021), might result in lower levels of defence induction. Secondly, there is a well-reported negative correlation between Si and carbon concentrations in plants (Cooke & Leishman, 2011Raven, 1983), which we also observed for perennial ryegrass in this study (Figure S3B-7).…”

“…In addition to being a constitutive defence (i.e. in place prior to herbivory), Si defences can be induced following herbivory (Johnson, Rowe, et al, 2020;Massey et al, 2007) in a short period of time (Waterman et al, 2021).…”