Data from: Locally and systemically induced glucosinolates follow optimal defence allocation theory upon root herbivory

1. Herbivore-induced defences in plants are considered a strategy to manage multiple interactions while saving resources. The optimal defence theory (ODT) is one of the most prominent theoretical frameworks to explain the defence allocation patterns within plants. It was recently shown that the ODT generally applies to constitutive glucosinolate (GSL) allocation in shoot and root organs. Previous studies showed that both root and shoot herbivore feeding may alter defence allocation over plant organs. For shoots, the effect depends on where the herbivores feed. It is as yet unknown whether similar principles apply to root-herbivore induced GSLs. 2. To analyse the effects of root localized herbivore feeding on GSL allocation, we conducted a pot experiment using Anomala cuprea grubs and four Brassicaceae; Brassica rapa, B. nigra, B. oleracea, and Sinapis alba. Individuals of these four plant species were grown in dedicated mesocosms. The grubs were confined either to the bottom soil, the middle section, or to the top soil. Plants grown in the same set-ups but without root herbivores served as controls. Glucosinolate levels of the leaf lamina, petiole, and stem as well as of the taproot, lateral roots, and fine roots were measured after eight days of herbivory. 3. Plant biomass reduction due to herbivory was the largest when herbivores were confined to the top soil. In the three Brassica species, taproot GSL levels increased upon herbivory independent of where the root herbivores were feeding. Glucosinolate levels in fine roots and shoots, on the other hand, hardly responded to root herbivory. Indole GSLs, which are more effective to pathogens than to herbivores, were more strongly induced than aliphatic and aromatic GSLs, especially in the taproots. Sinapis alba did not show remarkable increments in any GSL level upon herbivory. 4. These results show that locally and systemically induced defences in roots are consistent with the ODT: the taproot which is the most vulnerable and valuable to plant performance shows the highest increase in defence induction. The induced GSL profiles suggest that the response may not only target herbivores, but may also help to prevent secondary infection by microbial pathogens.1. 植物被草食动物诱导产生的防御被认为是一种在节约资源的同时调控多种生物互作的策略。最优防御理论（Optimal Defence Theory, ODT）是解释植物体内防御物质分配模式的最具影响力的理论框架之一。近期研究表明，该理论普遍适用于植物地上与地下器官的组成型硫代葡萄糖苷（glucosinolate, GSL）分配格局。既往研究显示，地上与地下草食动物的取食行为均会改变植物各器官的防御物质分配；对于地上组织而言，其防御响应模式取决于草食动物的取食位点。目前尚不清楚类似规律是否同样适用于地下草食动物诱导的硫代葡萄糖苷变化。 2. 为分析地下局部取食的草食动物对硫代葡萄糖苷分配的影响，本研究采用铜绿丽金龟（Anomala cuprea）蛴螬与4种十字花科（Brassicaceae）植物——芜菁（Brassica rapa）、黑芥（B. nigra）、甘蓝（B. oleracea）以及白芥（Sinapis alba）——开展盆栽实验。将这4种植物分别种植于专用中型实验生态系统（mesocosms）中，将蛴螬分别限定于盆钵的下层土壤、中层土壤或上层土壤；设置相同实验配置但未接种地下草食动物的组别作为对照组。经过8天的草食动物取食后，分别测定植株叶片（leaf lamina）、叶柄（petiole）、茎，以及主根（taproot）、侧根（lateral roots）与细根（fine roots）中的硫代葡萄糖苷含量。 3. 草食动物取食导致的植物生物量降低在其被限定于上层土壤时最为显著。在3种芸苔属（Brassica）植物中，无论地下草食动物的取食位点如何，主根中的硫代葡萄糖苷水平均会上升；而细根与地上部分的硫代葡萄糖苷水平则几乎未响应地下草食动物的取食。相较于脂肪族与芳香族硫代葡萄糖苷，对病原菌防御效果更佳的吲哚类硫代葡萄糖苷被更强程度地诱导，这一现象在主根中尤为明显。白芥（Sinapis alba）在取食处理后未出现任何硫代葡萄糖苷水平的显著升高。 4. 上述结果表明，植物地下部分的局部与系统性诱导防御符合最优防御理论：主根作为对植物适合度与生存最为关键且脆弱的器官，其防御诱导程度最高。诱导产生的硫代葡萄糖苷谱型提示，该响应不仅可靶向草食动物，还可能帮助植物抵御微生物病原菌的次生侵染。