茉莉酸在植物诱导防御中的作用

茉莉酸(JA)和茉莉酸甲酯(MeJA)作为与损伤相关的植物激素和信号分子,广泛地存在于植物体中,外源应用能够激发防御植物基因的表达,诱导植物的化学防御,产生与机械损伤和昆虫取食相似的效果。大量研究表明,用茉莉酸类化合物处理植物可系统诱导蛋白酶抑制剂(PI)和多酚氧化酶(PPO),从而影响植食动物对营养物质的吸收,还能增加过氧化物酶、壳聚糖酶和脂氧合酶等防御蛋白的活性水平,导致生物碱和酚酸类次生物质的积累,增加并改变挥发性信号化合物的释放,甚至形成防御结构,如毛状体和树脂导管。经茉莉酸处理的植物提高了植食动物的死亡率,变得更加吸引捕食性和寄生性天敌。挥发性化合物——茉莉酸甲酯可以从植物的气孔进入植物体内,在细胞质中被酯酶水解为茉莉酸,实现长距离的信号传导和植物间的交流,诱导邻近植物产生诱导防御反应。茉莉酸和茉莉酸甲酯分别具有4种立体异构,其中具有活性的是顺式结构,但顺式结构不稳定,会差向异构化为反式结构。茉莉酸的代谢物(Z)-茉莉酮(cis-Jasmone)具电生理活性,在植物诱导防御中起作用,并且在防御信号的作用上不同于茉莉酸和茉莉酸甲酯。

The function of Jasmonic acid in induced plant defence

Jasmonic acid (JA) and methyl jasmonate (MeJA) are wound-related hormone and signal molecules found in most plants that, when applied exogenously, can stimulate the defensive genes to increase the chemical levels of induced defenses in the patterns similar to those induced by wounding or insect feeding. Numerous studies show that they can systemically activate the activity of proteinase inhibitors (PI) and polyphenol oxidases (PPO) in the treated plants, which appear to function as an anti-nutritive defense against herbivores. Jasmonic acid and methyl jasmonate can also increase the level of activity of other defensive proteins such as peroxidase (POX), Chitinase and lipoxygenase(LOX), resulting in the accumulation of some secondary metabolites, including alkaloid and phenolic compounds, as well as the emission of volatiles and the formation of defensive structures, such as trichomes and traumatic resin ducts. Thus, the toxic effect of the treated plants increases herbivore mortality while the volatiles attract more parasitoids and herbivore predators than uninduced plants. The airborne phase compound , methyl jasmonate, can realize long-distance signal transportation through hydrolyzing to jasmonic acid, enabling communication among the contiguous plants. Jasmonate consists of a cyclopentane ring with a ketone group. They have four possible stereoisomers respectively since the chiral center can have either an R or S absolute configuration. The cis orientation is more biologically active but less stable, and will epimerize to the more stable trans configuration (Z)-jasmone, a volatile metabolite of jasmonic acid and electrophysiologically active to insects, while its possible signaling role is qualitatively different from that of the biosynthetically related JA and MeJA.