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The role of plant silicon (Si) in the alleviation of abiotic and biotic stress is now widely recognised and researched. Amongst the biotic stresses, Si is known to increase resistance to herbivores through biomechanical and chemical mechanisms, although the latter are indirect and remain poorly characterised. Chemical defences are principally regulated by several antiherbivore phytohormones. The jasmonic acid (JA) signalling pathway is particularly important and has been linked to Si supplementation, albeit with some contradictory findings. In this Perspectives article, we summarise existing knowledge of how Si affects JA in the context of herbivory and present a conceptual model for the interactions between Si and JA signalling in wounded plants. Further, we use novel information from the model grass Brachypodium distachyon to underpin aspects of this model. We show that Si reduces JA concentrations in plants subjected to chemical induction (methyl jasmonate) and herbivory ( Helicoverpa armigera ) by 34% and 32%, respectively. Moreover, +Si plants had 13% more leaf macrohairs than −Si plants. From this study and previous work, our model proposes that Si acts as a physical stimulus in the plant, which causes a small, transient increase in JA. When +Si plants are subsequently attacked by herbivores, they potentially show a faster induction of JA due to this priming. +Si plants that have already invested in biomechanical defences (e.g. macrohairs), however, have less utility for JA-induced defences and show lower levels of JA induction overall.

Grasses are hyper-accumulators of silicon (Si), which is known to alleviate diverse environmental stresses, prompting speculation that Si accumulation evolved in response to unfavourable climatic conditions, including seasonally arid environments. We conducted a common garden experiment using 57 accessions of the model grass Brachypodium distachyon, sourced from different Mediterranean locations, to test relationships between Si accumulation and 19 bioclimatic variables. Plants were grown in soil with either low or high (Si supplemented) levels of bioavailable Si. Si accumulation was negatively correlated with temperature variables (annual mean diurnal temperature range, temperature seasonality, annual temperature range) and precipitation seasonality. Si accumulation was positively correlated with precipitation variables (annual precipitation, precipitation of the driest month and quarter, and precipitation of the warmest quarter). These relationships, however, were only observed in low-Si soils and not in Si-supplemented soils. Our hypothesis that accessions of B. distachyon from seasonally arid conditions have higher Si accumulation was not supported. On the contrary, higher temperatures and lower precipitation regimes were associated with lower Si accumulation. These relationships were decoupled in high-Si soils. These exploratory results suggest that geographical origin and prevailing climatic conditions may play a role in predicting patterns of Si accumulation in grasses.

The use of light-blocking film (LBF) is a promising strategy to reduce energy consumption in high-tech glasshouses. However, it also reduces specific light spectra which affect the physiological responses of plants. The LBF reduces 8–25% of canopy-level photosynthetically active radiation (PAR) while targeting a reduction in biologically irrelevant heat-generating light. Here, we investigated the mesophyll and stomatal responses of a Capsicum annum genotype grown in a high-tech glasshouse facility under the LBF. Our results demonstrated that LBF significantly increased the rate of stomatal closure to stimulus (exogenously applied ABA). The capsicum crops grown under LBF also exhibited significantly faster stomatal response to changes in light intensities (e.g. low to high PAR), rather than to light spectral differences (e.g. blue light that induces stomatal opening), which are potentially due to upregulated expression of photoreceptors and light harvesting genes [Phototropin 1 (PHOT1), phytochrome A (PHYA) and Ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (RBCS)] in guard cells. Moreover, capsicum leaves under LBF also exhibited faster electron physiological responses to light intensity in mesophyll rather than to red light spectrum, which determines electron transfer in mesophyll for photosynthesis. However, leaf mesophyll in LBF showed enhanced K+ and Cl− efflux, Ca2+ influx, and reduced capability in proton pumping than those under control conditions, suggesting impaired mesophyll cell ion homeostasis in LBF. We propose that the LBF significantly affected stomatal responses to the light, which is partially linked with its modified mesophyll ionic status required for optimal photosynthesis in glasshouse capsicum plants.

Atmospheric carbon dioxide (CO 2 ) concentration has increased significantly and is projected to double by 2100. To increase current food production levels, understanding how pests and diseases respond to future climate driven by increasing CO 2 is imperative. We investigated the effects of elevated CO 2 (eCO 2 ) on the interactions among wheat (cv. Yitpi), Barley yellow dwarf virus and an important pest and virus vector, the bird cherry-oat aphid ( Rhopalosiphum padi ), by examining aphid life history, feeding behavior and plant physiology and biochemistry. Our results showed for the first time that virus infection can mediate effects of eCO 2 on plants and pathogen vectors. Changes in plant N concentration influenced aphid life history and behavior and N concentration was affected by virus infection under eCO 2 . We observed a reduction in aphid population size and increased feeding damage on noninfected plants under eCO 2 but no changes to population and feeding on virus-infected plants irrespective of CO 2 treatment. We expect potentially lower future aphid populations on noninfected plants but no change or increased aphid populations on virus-infected plants therefore subsequent virus spread. Our findings underscore the complexity of interactions between plants, insects and viruses under future climate with implications for plant disease epidemiology and crop production.