What is the Most Effective Jasmonates Form in Promoting Tomato and Maize Defense Responses to Spodoptera exiguaHerbivory?

Jasmonates proposed to have a prospective key role in the plant insect interaction. This study conducted to clarify the role played by JA and its derivatives in defense responses of tomato and maize to Spodoptera exigua infestation. Chlorophyll a/b ratio, soluble carbohydrates, proteins and amino acids content measured in infested plants and uninfested controls after 2 h, 2 days and 1 week of infestation. JA, MeJA and JA-L-Ile were quantified using HPLC-MS/MS under the same experimental conditions. The results show that S. exigua attack did not change Chl a/b ratio in tomato, while maize recorded a greater adaptability at the beginning of the infestation by decreasing Chl a/b ratio. Soluble carbohydrates content did not change in infested tomato leaves compared to control, while increased in infested maize at 2 h and 2 days. Free amino acids content reduced lower than control in tomato leaves at all observed time periods due to S. exigua attack, while in maize higher concentrations of free amino acids accumulated in infested plants after 2 h and 2 days. In both plants, S. exigua infestation induced JA, MeJA and JA-L-Ile to high levels at 2 h then, decreased gradually by increasing infestation time. JA concentration in infested maize was much higher than that in infested tomato leaves. However, MeJA and JA-L-Ile concentration in infested tomato leaves was higher than that in maize. In control plants, JA did not record, while MeJA recorded in comparable values both in tomato and maize. Therefore, JA assumed to play the main role in increasing defense responses to S. exigua. infestation as a direct signaling molecule, however MeJA could play an indirect role by inducing JA accumulation.茉莉酸类物质（Jasmonates）被认为在植物与昆虫的互作中具有潜在关键作用。本研究旨在阐明茉莉酸（JA）及其衍生物在番茄与玉米受甜菜夜蛾（Spodoptera exigua）侵染时的防御反应中所发挥的作用。本研究在侵染2小时、2天及1周后，对受侵染植株与未侵染对照组的叶绿素a/b比值、可溶性碳水化合物、蛋白质及氨基酸含量进行了测定。茉莉酸（JA）、茉莉酸甲酯（MeJA）及茉莉酰-L-异亮氨酸（JA-L-Ile）在相同实验条件下采用高效液相色谱-串联质谱（HPLC-MS/MS）进行定量分析。研究结果显示，甜菜夜蛾侵染并未改变番茄的叶绿素a/b比值，而玉米在侵染初期通过降低叶绿素a/b比值展现出更强的适应性。受侵染番茄叶片的可溶性碳水化合物含量与对照组相比无显著变化，而受侵染玉米在侵染2小时及2天时的可溶性碳水化合物含量显著升高。在所有观测时段内，甜菜夜蛾侵染导致番茄叶片的游离氨基酸含量均低于对照组；而玉米在侵染2小时及2天时，受侵染植株体内的游离氨基酸浓度显著升高。两种作物均在侵染2小时后，因甜菜夜蛾侵染使JA、MeJA及JA-L-Ile的含量升至较高水平，随后随侵染时间延长逐渐下降。受侵染玉米体内的JA浓度显著高于受侵染番茄叶片，而受侵染番茄叶片的MeJA及JA-L-Ile浓度则高于玉米。对照组植株中未检测到JA，而番茄与玉米体内的MeJA含量处于相近水平。因此，JA作为直接信号分子，在增强植物对甜菜夜蛾侵染的防御反应中发挥主要作用；而MeJA则可通过诱导JA积累间接参与防御过程。