Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
Department of Chemistry, The Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ, UK.
New Phytol. 2013 Sep;199(4):916-924. doi: 10.1111/nph.12354. Epub 2013 Jun 12.
The metal hyperaccumulator plant Noccaea caerulescens is protected from disease by the accumulation of high concentrations of metals in its aerial tissues, which are toxic to many pathogens. As these metals can lead to the production of damaging reactive oxygen species (ROS), metal hyperaccumulator plants have developed highly effective ROS tolerance mechanisms, which might quench ROS-based signals. We therefore investigated whether metal accumulation alters defence signalling via ROS in this plant. We studied the effect of zinc (Zn) accumulation by N. caerulescens on pathogen-induced ROS production, salicylic acid accumulation and downstream defence responses, such as callose deposition and pathogenesis-related (PR) gene expression, to the bacterial pathogen Pseudomonas syringae pv. maculicola. The accumulation of Zn caused increased superoxide production in N. caerulescens, but inoculation with P. syringae did not elicit the defensive oxidative burst typical of most plants. Defences dependent on signalling through ROS (callose and PR gene expression) were also modified or absent in N. caerulescens, whereas salicylic acid production in response to infection was retained. These observations suggest that metal hyperaccumulation is incompatible with defence signalling through ROS and that, as metal hyperaccumulation became effective as a form of elemental defence, normal defence responses became progressively uncoupled from ROS signalling in N. caerulescens.
金属超积累植物节节菜通过在其地上组织中积累高浓度的金属来抵御疾病，这些金属对许多病原体是有毒的。由于这些金属可能导致有害的活性氧（ROS）的产生，金属超积累植物已经开发出了高度有效的 ROS 耐受机制，这些机制可能会淬灭基于 ROS 的信号。因此，我们研究了金属积累是否通过 ROS 改变了这种植物的防御信号。我们研究了锌（Zn）积累对节节菜中病原菌诱导的 ROS 产生、水杨酸积累以及下游防御反应（如胼胝质沉积和病程相关（PR）基因表达）的影响，病原菌为丁香假单胞菌 pv. maculicola。Zn 的积累导致节节菜中超氧阴离子的产生增加，但丁香假单胞菌的接种并没有引发大多数植物典型的防御性氧化爆发。依赖 ROS 信号（胼胝质和 PR 基因表达）的防御也在节节菜中被修饰或缺失，而对感染的水杨酸产生则保留下来。这些观察结果表明，金属超积累与 ROS 防御信号不兼容，并且随着金属超积累作为一种元素防御形式变得有效，正常的防御反应在节节菜中逐渐与 ROS 信号脱钩。
