Some plant species accumulate selenium in their tissues in quantities far above soil concentrations, and experiments demonstrate that selenium can serve as a defence against herbivores and pathogens. However, selenium may also cause oxidative stress and reduce growth in plants. We measured growth, selenium accumulation and herbivory in four varieties of the selenium accumulator Brassica juncea to investigate the cost of accumulation as well as its benefit in reducing herbivory. We measured selenium levels, plant size and flower number in four varieties of B. juncea watered with sodium selenate or treated as controls. We also conducted no-choice herbivory trials on leaves from both treatments with the specialist herbivore Pieris rapae. The selenate treatment slightly increased leaf number over the control, but tissue concentrations of selenium and flower number were negatively correlated in some varieties. In herbivory trials, leaves from the plants in the selenate treatment lost less leaf tissue, and the majority of larvae given leaves from selenate-treated plants ate very little leaf tissue at all. In the variety with the highest selenium accumulation, leaves from selenate-treated plants that showed reduced flower production also experienced less herbivory in feeding trials. The protective advantage of greater selenium accumulation may be offset by negative effects on reproduction, and the relatively low level of selenium accumulation in this species as compared to more extreme hyperaccumulators could reflect the minimum level necessary to enhance protection from herbivory.

中文翻译：

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芥菜硒积累的防御效益和花数成本。

一些植物物种在其组织中积累的硒含量远远高于土壤浓度，实验表明硒可以防御食草动物和病原体。然而，硒也可能引起氧化应激并降低植物的生长。我们测量了四个硒积累植物芥菜品种的生长、硒积累和食草行为，以研究积累的成本及其在减少食草行为方面的效益。我们测量了用硒酸钠浇灌或作为对照处理的四种芥菜的硒含量、植株大小和花朵数量。我们还对专业食草动物菜青虫的两种处理的叶子进行了无选择食草试验。与对照相比，硒酸盐处理略微增加了叶片数量，但在某些品种中，硒的组织浓度与花数量呈负相关。在食草试验中，经过硒酸盐处理的植物叶子损失的叶子组织较少，并且大多数幼虫吃经过硒酸盐处理的植物叶子时只吃很少的叶子组织。在硒积累量最高的品种中，经硒酸盐处理的植物的叶子显示出开花量减少，在饲喂试验中也经历了较少的草食性。较高的硒积累的保护优势可能会被对繁殖的负面影响所抵消，并且与更极端的超积累植物相比，该物种的硒积累水平相对较低，这可能反映了增强对草食性的保护所需的最低水平。