Pike Sharon M, Zhang Xue-Cheng, Gassmann Walter
Department of Plant Microbiology and Pathology, University of Missouri, Columbia, Missouri 65211-7310, USA.
Plant Physiol. 2005 Jun;138(2):1009-17. doi: 10.1104/pp.104.047142. Epub 2005 May 20.
The hypersensitive response (HR) is defined as rapid cell collapse at the infection site and often accompanies plant resistance. The physiological processes leading to HR are not well understood. Here, we report an electrophysiological characterization of bacterial HR caused by a single avirulence gene in the absence of other bacterial signals. We used dexamethasone (dex)-inducible transgenic Arabidopsis (Arabidopsis thaliana) plants containing the avrRpt2 gene from Pseudomonas syringae pv tomato. Membrane depolarization in these plants began 1 to 1.5 h after dex application, hours before electrolyte leakage. Progressive depolarization was a sensitive early indicator of HR that occurred only in Arabidopsis leaf cells expressing both avrRpt2 and a functional RPS2 gene. Hyperpolarization of fully depolarized membranes by fusicoccin, a fungal toxin that activates the H(+)-ATPase, indicates that depolarization did not result from a nonfunctional pump or leaky membranes. Depolarization and electrolyte leakage were inhibited in RPS2 plants by the calcium channel blocker LaCl(3), highly correlating these events and suggesting that Ca(2+) entry into cells is required for both. Also correlated were inhibition of depolarization, electrolyte leakage, and HR following salicylic acid pretreatment. In salicylic acid-pretreated RPS2 seedlings, avrRpt2 transcript was produced after dex treatment. However, AvrRpt2 protein accumulation was greatly reduced, suggesting a possible mechanism for inhibition of HR in plants with induced resistance. This experimental system is a very sensitive assay that lends itself to the dissection of physiological processes leading to HR in plants, and provides a baseline for future research within a genetic framework.
过敏反应（HR）被定义为感染部位细胞的快速坏死，且常伴随植物抗性。导致过敏反应的生理过程尚未完全明晰。在此，我们报告了在无其他细菌信号情况下，由单个无毒基因引发的细菌过敏反应的电生理特性。我们使用了含丁香假单胞菌番茄致病变种avrRpt2基因的地塞米松（dex）诱导型转基因拟南芥植株。在施加dex后1至1.5小时，这些植株的膜电位开始去极化，早于电解质渗漏数小时。渐进性去极化是过敏反应的一个敏感早期指标，仅在同时表达avrRpt2和功能性RPS2基因的拟南芥叶细胞中出现。由激活H(+) - ATP酶的真菌毒素藤霉素使完全去极化的膜发生超极化，这表明去极化并非由无功能的泵或渗漏的膜导致。钙通道阻滞剂LaCl(3)抑制了RPS2植株中的去极化和电解质渗漏，高度关联了这些事件，并表明细胞外Ca(2+)内流对二者均是必需的。水杨酸预处理后去极化、电解质渗漏及过敏反应的抑制也存在相关性。在水杨酸预处理的RPS2幼苗中，dex处理后产生了avrRpt2转录本。然而，AvrRpt2蛋白积累大幅减少，这提示了诱导抗性植物中过敏反应受抑制的一种可能机制。该实验系统是一种非常灵敏的检测方法，有助于剖析导致植物过敏反应的生理过程，并为遗传框架下的未来研究提供了一个基线。
