Zeier Jürgen, Pink Bianka, Mueller Martin J, Berger Susanne
Julius-von-Sachs-Institute of Biological Science, University of Würzburg, Julius-von-Sachs-Platz 3, 97082, Germany.
Planta. 2004 Aug;219(4):673-83. doi: 10.1007/s00425-004-1272-z. Epub 2004 Apr 20.
In incompatible plant-pathogen interactions, disease resistance is generated by rapid activation of a multitude of plant defence reactions. Little is known about the dependency of these resistance responses on external factors. The plasticity of plant defence mechanisms in terms of light conditions is studied here. Interaction of Arabidopsis thaliana (L.) Heynh. with an avirulent strain of Pseudomonas syringae pv. maculicola in the dark resulted in increased apoplastic bacterial growth and therefore reduced local resistance as compared to an infection process in the presence of light. Several characteristic defence reactions, including activation of phenylalanine ammonia-lyase, accumulation of salicylic acid (SA), expression of the pathogenesis-related protein PR-1 and the development of a microscopically defined hypersensitive response, proved to be light dependent. In contrast, the extent of the oxidative burst, as estimated by induction of the protectant gene glutathione- S-transferase, was not weakened by the absence of light. Moreover, pathogen-induced accumulation of jasmonic acid, production of the phytoalexin camalexin and transcriptional induction of a pathogen-inducible myrosinase were even more pronounced in the dark. Apart from affecting local defence responses, light also influenced the establishment of systemic acquired resistance (SAR). SAR development in response to infection by avirulent bacteria was completely lost when the primary infection process occurred in the absence of light. SAR developed both under medium (70 micromol photons m(-2) s(-1)) and strong (500 micromol photons m(-2) s(-1)) light conditions but was in the latter case not associated with an accumulation of SA and PR-1 in systemic leaves, demonstrating that SAR can be executed independently from these molecular SAR markers. Our results are consistent with the notion that SA accumulation in infected primary leaves is necessary for induction of systemic resistance and indicate that defence mechanisms different from SA signalling and PR-protein action exist in systemic tissue to confer resistance during SAR.
在不亲和的植物-病原体互作中，植物通过快速激活多种防御反应来产生抗病性。对于这些抗性反应对外部因素的依赖性，人们了解甚少。本文研究了植物防御机制在光照条件方面的可塑性。拟南芥（Arabidopsis thaliana (L.) Heynh.）与丁香假单胞菌番茄致病变种（Pseudomonas syringae pv. maculicola）的无毒菌株在黑暗中互作时，相比于在有光照条件下的感染过程，会导致质外体细菌生长增加，从而局部抗性降低。包括苯丙氨酸解氨酶的激活、水杨酸（SA）的积累、病程相关蛋白PR-1的表达以及微观定义的过敏反应的发展等几种典型防御反应，都被证明是依赖光照的。相比之下，通过诱导保护基因谷胱甘肽-S-转移酶来估计的氧化爆发程度，并不会因缺乏光照而减弱。此外，病原体诱导的茉莉酸积累、植保素camalexin的产生以及病原体诱导的黑芥子酶的转录诱导在黑暗中甚至更加明显。除了影响局部防御反应外，光照还影响了系统获得性抗性（SAR）的建立。当初次感染过程在无光照条件下发生时，对无毒细菌感染的SAR发展完全丧失。在中等光照（70微摩尔光子·米-2·秒-1）和强光（500微摩尔光子·米-2·秒-1）条件下都能发展出SAR，但在后一种情况下，系统叶片中SA和PR-1不会积累，这表明SAR可以独立于这些分子SAR标记进行。我们的结果与以下观点一致，即感染的初生叶片中SA的积累对于诱导系统抗性是必要的，并且表明在系统组织中存在不同于SA信号传导和PR蛋白作用的防御机制，以在SAR期间赋予抗性。
