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

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.

硅（Silicon, Si）可对植食性昆虫产生不利影响，尤其在那些演化出大量积累硅能力的植物中。近期已有研究证实植食作用可快速诱导硅积累，但该过程为植物提供的抗虫防护水平仍不明确。本研究以硅超富集模式禾本科植物二穗短柄草（Brachypodium distachyon）为材料，将其暴露于咀嚼式植食昆虫棉铃虫（Helicoverpa armigera）的取食胁迫下，并设置三种培养条件：34天持续供硅组（+Si）、全程不供硅组（-Si）以及植食开始后供硅组（-Si→+Si）。本研究评估了各组硅处理对降低植食昆虫取食适应性的效果，并测定了硅基防御物质与酚类物质（另一类常受硅调控的防御物质）。尽管-Si→+Si组植株的硅浓度仍处于较低水平，但在施加硅后的72小时内，该组植株的抗虫性已与+Si组相当。与全程不供硅的-SI组相比，+Si组与-Si→+Si组均能降低植食昆虫的取食危害与生长发育，并增加其上颚磨损程度。植食作用发生6小时后，-Si→+Si组植株的充硅细胞密度显著升高；而在24小时内，该组的充硅细胞密度已与+Si组无显著差异，但仅+Si组出现了酚类物质含量的下降。本研究证实，短期供硅的植株可快速积累硅基抗虫防御物质，其效果与长期供硅的植株相当。