Ogawa Daisuke, Nakajima Nobuyoshi, Tamaoki Masanori, Aono Mitsuko, Kubo Akihiro, Kamada Hiroshi, Saji Hikaru
Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Planta. 2007 Oct;226(5):1277-85. doi: 10.1007/s00425-007-0556-5. Epub 2007 Jun 23.
Ozone (O3), a major photochemical oxidant, causes leaf injury in plants. Plants synthesize salicylic acid (SA), which is reported to greatly affect O3 sensitivity. However, the mechanism of SA biosynthesis under O3 exposure remains unclear. Plants synthesize SA either by a pathway involving phenylalanine as a substrate or another involving isochorismate. To clarify how SA is produced in O3-exposed Arabidopsis, we examined the activities of phenylalanine ammonia lyase (PAL) and isochorismate synthase (ICS), which are components of the phenylalanine and isochorismate pathways, respectively. Exposure of Arabidopsis to O3 enhanced the accumulation of SA and the increase of ICS activity but did not affect PAL activity. In sid2 mutants, which have a defect in ICS1, the level of SA and the activity of ICS did not increase in response to O3 exposure. These results suggest that SA is mainly synthesized from isochorismate in Arabidopsis. Furthermore, the level of ICS1 expression and the activity of ICS during O3 exposure elevated in plants deficient for SA signaling (npr1 and eds5 mutants and NahG transgenics). Treatment of plants with SA also suppressed the enhancement of ICS1 expression by O3. These results suggest that SA synthesis is negatively regulated by SA signaling.
臭氧（O₃）是一种主要的光化学氧化剂，会对植物叶片造成损伤。植物合成水杨酸（SA），据报道其对O₃敏感性有很大影响。然而，在O₃暴露下SA生物合成的机制仍不清楚。植物通过以苯丙氨酸为底物的途径或另一条以异分支酸为底物的途径合成SA。为了阐明在暴露于O₃的拟南芥中SA是如何产生的，我们检测了苯丙氨酸解氨酶（PAL）和异分支酸合酶（ICS）的活性，它们分别是苯丙氨酸途径和异分支酸途径的组成部分。将拟南芥暴露于O₃会增强SA的积累和ICS活性的增加，但不影响PAL活性。在ICS1有缺陷的sid2突变体中，SA水平和ICS活性在O₃暴露后没有增加。这些结果表明，在拟南芥中SA主要由异分支酸合成。此外，在缺乏SA信号传导的植物（npr1和eds5突变体以及NahG转基因植物）中，O₃暴露期间ICS1的表达水平和ICS的活性升高。用SA处理植物也抑制了O₃对ICS1表达的增强作用。这些结果表明，SA信号传导对SA合成起负调控作用。
