Key Laboratory of Horticultural Plant Biology of Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, China.
J Plant Physiol. 2012 Aug 15;169(12):1143-9. doi: 10.1016/j.jplph.2012.03.018. Epub 2012 Jun 1.
Citrus canker caused by Xanthomonas axonopodis pv. citri (Xac) is a devastating bacterial disease threatening the citrus industry. Salicylic acid (SA) plays a key role in plant defense response to biotic stress, but information is scarce concerning the application of SA to enhancing Xac resistance. In the present research attempts were made to investigate how exogenous application of SA influenced canker disease outbreak in navel orange (Citrus sinensis). Exogenously applied SA at 0.25 mM significantly enhanced the endogenous free and bound SA, particularly the latter. Upon exposure to Xac, lower disease incidence rate and smaller lesion sites were observed in the samples pre-treated with SA, accompanied by repression of bacterial growth at the lesion sites. Concurrent with the augmented disease resistance, SA-treated leaves had higher H₂O₂ level and smaller stomata apertures before or after Xac infection when compared with their counterparts pre-treated with water (control). SA treatment elevated the activities of phenylalanine ammonia-lyase and β-1,3-glucanase, but only the latter was higher in the SA-treated samples after Xac infection. In addition, mRNA levels of two pathogenesis-related genes, CsCHI and CsPR4A, were higher in the SA-treated samples relative to the control. Taken together, our results strongly suggest that the exogenously applied SA has evoked a cascade of physiological and molecular events that function singly or in concert to confer resistance to Xac invasion.
由柑橘溃疡病菌（Xanthomonas axonopodis pv. citri，Xac）引起的柑橘溃疡病是一种严重威胁柑橘产业的细菌性病害。水杨酸（SA）在植物对生物胁迫的防御反应中起着关键作用，但关于应用 SA 来增强对 Xac 的抗性的信息却很少。在本研究中，试图研究外源施用 SA 如何影响脐橙（Citrus sinensis）溃疡病的爆发。0.25 mM 的外源 SA 显著提高了内源游离和结合的 SA，尤其是后者。在暴露于 Xac 后，用 SA 预处理的样品中观察到较低的发病率和较小的病变部位，同时在病变部位抑制了细菌的生长。与对照（用清水预处理）相比，具有增强的抗病性的同时，SA 处理的叶片在 Xac 感染前后具有更高的 H₂O₂水平和更小的气孔开度。SA 处理提高了苯丙氨酸解氨酶和β-1,3-葡聚糖酶的活性，但只有在 Xac 感染后，SA 处理的样品中的后者更高。此外，与对照相比，两个病程相关基因 CsCHI 和 CsPR4A 的 mRNA 水平在 SA 处理的样品中更高。总之，我们的结果强烈表明，外源施用的 SA 引发了一系列生理和分子事件，这些事件单独或协同作用赋予了对 Xac 入侵的抗性。
