Abstract
Environmental factors controlling silicon (Si) accumulation in terrestrial plant are key drivers to alleviate plant biotic stresses, including insect herbivory. While there is a general agreement on the ability of Si-enriched plant to better resist insect feeding, recent studies suggest that Si also primes biochemical defense pathways in various plant families. In this review, we first summarize how soil parameters and climate variables influence Si assimilation in plants. Then, we describe recent evidences on the ability of Si to modulate plant volatile emissions, with potential cascade effects on phytophagous insects and higher trophic levels. Even though the mechanisms still need to be elucidated, Si accumulation in plants leads to contrasting effects on the levels of the three major phytohormones, namely jasmonic acid, salicylic acid and ethylene, resulting in modified emissions of plant volatile organic compounds. Herbivore-induced plant volatiles would be particularly impacted by Si concentration in plant tissues, resulting in a cascade effect on the attraction of natural enemies of pests, known to locate their prey or hosts based on plant volatile cues. Since seven of the top 10 most important crops in the world are Si-accumulating Poaceae species, it is important to discuss the potential of Si mobility in soil-plant systems as a novel component of an integrated pest management.
Highlights
Through its high abundance and relative high mobility in terrestrial environments, silicon (Si) is an ubiquitous element in the soil-plant system [1,2,3]
Plants characterized by high concentration of Si show higher expression of genes encoding for defensive enzymes, including phenylalanine ammonia lyase, lipoxygenase and polyphenol oxidase [18,19]
Si [90]: Using wild type (WT) and silicon-deficient mutant OsLsi1 rice plants, they showed that the expression levels of jasmonic acid (JA) dependent genes (OsLOX, OsAOS2, OsCOI1a, OsCOI1b and OsBBPI) were much higher in Si-treated WT plants after infestation by C. medinalis, including transcripts encoding proteins involved in JA signaling, and defenses-related enzymes (catalase (CAT), superoxide dismutase (SOD) polyphenol oxidase (PPO) and peroxidase (POD)
Summary
Through its high abundance and relative high mobility in terrestrial environments, silicon (Si) is an ubiquitous element in the soil-plant system [1,2,3]. Si accumulates as amorphous hydrated silica (SiO2 ·nH2 O) in the plant epidermal cells [7,8,9], increasing the hardness and abrasiveness of plant tissues, impacting oral parts of phytophagous insects and reducing food intake [10,11]. There is evidences that Si, in non-accumulator species, induces changes in plant nutritional quality and reduce performance of insect herbivore [16]; Silicon is involved in the biochemical response of plants against the attack of a phytophagous insect [17]. Plants characterized by high concentration of Si show higher expression of genes encoding for defensive enzymes, including phenylalanine ammonia lyase, lipoxygenase and polyphenol oxidase [18,19] This results in higher levels of defensive compounds, such as phenolics or phytoalexins [20,21]. This research was conducted between December 2018 and September 2019 and the resulting references were selected or rejected based on the abstracts of the published papers
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