羟自由基激活的钾离子通道参与胁迫诱导的细胞凋亡

Conflux + I&E Flux + I&M Flux = 细胞内外离子/分子同时检测完整方案

活性氧（ROS）是植物体中重要的毒性及调控物质，受一系列生物及非生物胁迫、激素、发育及重力信号、矿物质代谢缺失等诱导产生。目前，人们已经发现了包括MAPK激酶、转录因子等在内的许多活性氧感知系统。此外，质膜离子通道也可能参与植物的活性氧感知及活性氧介导的调控反应。活性氧的质膜离子通道在动物关键生理功能中的重要作用已经比较明确，但在植物中，此类离子通道特别是羟自由基（HR）激活的K+通道的性质及功能尚不清楚。

2010年4月7日，英国的科学家Demidchik等人选用野生型（WT）及K+外流通道基因缺失突变体（gork1-1）的拟南芥为研究对象，应用非损伤微测技术、电子顺磁共振（EPR）、膜片钳，以及细胞成像等方法研究了不同处理条件下拟南芥根及其原生质体的K+流速、氧自由基、膜电位、凋亡细胞形态等指标。研究发现，HR及胁迫均可引起拟南芥幼苗根部产生明显的K+外流，但突变体中外流明显较弱。NaCl可诱导根部产生HR进而激活K+通道。突变体gork1-1、经过K+通道抑制剂或HR清除剂处理过的野生型拟南芥根部细胞凋亡比较缓慢。由此得出，植物中HR激活的K+通道也参与了细胞凋亡。

此研究结果提出了ROS调控植物阳离子运输的一个新观点，并阐述了HR激活的K+通道在植物中的生理作用。

关键词：钾离子（Potassium）、细胞程序性死亡（Programmed cell death）、 活性氧（Reactive oxygen species）、胁迫（Stress）

参考文献：Demidchik et al. J. Cell Sci. doi: 10.1242/jcs.064352

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ABSTRACT:

Reactive oxygen species (ROS are central to plant stress response, signalling, development and a multitude of other processes. In this study, the plasma-membrane hydroxyl radical (HR-activated K+ channel responsible for K+ efflux from root cells during stress accompanied by ROS generation is characterised. The channel showed 16-pS unitary conductance and was sensitive to Ca2+, tetraethylammonium, Ba2+, Cs+ and free-radical scavengers. The channel was not found in the gork1-1 mutant, which lacks a major plasma-membrane outwardly rectifying K+ channel. In intact Arabidopsis roots, both HRs and stress induced a dramatic K+ efflux that was much smaller in gork1-1 plants. Tests with electron paramagnetic resonance spectroscopy showed that NaCl can stimulate HR generation in roots and this might lead to K+-channel activation. In animals, activation of K+-efflux channels by HRs can trigger programmed cell death (PCD. PCD symptoms in Arabidopsis roots developed much more slowly in gork1-1 and wild-type plants treated with K+-channel blockers or HR scavengers. Therefore, similar to animal counterparts, plant HR-activated K+ channels are also involved in PCD. Overall, this study provides new insight into the regulation of plant cation transport by ROS and demonstrates possible physiological properties of plant HR-activated K+ channels.