以温室中培养的龙井43茶树2年生扦插苗为实验材料,采用分光光度计法测定了正常茶树叶片中多酚氧化酶(PPO)活性变化的日节律,以及茉莉酸甲酯(MeJA)处理和机械损伤诱导不同叶位叶片PPO活性的时序变化.结果表明:正常茶树叶片中PPO活性高峰出现在4:00;MeJA处理茶树30 h后,其叶片PPO活性与对照间呈现显著差异,于处理后174 h达到最高峰;半定量RT-PCR检测结果发现,MeJA诱导茶树叶片PPO基因表达量最高峰出现在处理后126 h,比生化测定结果提前了48 h.机械损伤可诱导处理叶及其下叶位叶片PPO活性迅速升高,表现出一定系统性;机械损伤叶片与系统诱导叶片间PPO活性随时间变化的趋势基本平行,但机械损伤叶片中PPO活性始终高于系统诱导叶片.本研究证明,MeJA和机械损伤均可诱导茶树叶片中PPO活性的显著增强,进一步证实茉莉酸(JA)信号转导途径在茶树的直接防御反应中具有重要作用.
Polyphenol oxidase(PPO) plays an important role in defending herbivorous insects.Our objectives were to illuminate the kinetics of polyphenol oxidase activity of healthy plant,induced by(methyl jasmonate) MeJA,mechanical damage and systemic induction by mechanical damage.2-yr-old Longjing tea plants were used.Circadian kinetics of PPO activity was measured by spectrophotometer.RT-PCR was used to confirm the kinetics of polyphenol oxidase gene expression quantity of MeJA treated samples,in order to give proof of the bio-chemistry results.The activity peak occurred at 4 am in intact tea leaves.The activity of PPO was significantly different between MeJA treated leaves and controls at 30 h,mounted the peak at 174 h.Results of RT-PCR showed that gene expression quantity mounted the peak at 126 h,about 48 h ahead of enzymatic activity analysis.Mechanical damage induced PPO activity significantly increase not only in treatment leaf,but also in lower position leaf,which showed systematic reaction.PPO activities were similar in intact leaves in different position.Following mechanical demage,PPO activity increased dramatically and systemically.In systemically wounded leaves,PPO activity changed in parallel to the induction observed in wounded leaves generally,but the increase was consistently slower.Our results showed that elevation of PPO activity could be significantly induced by exogenous application of MeJA and mechanical damage,suggesting that JA signaling pathway may also play an important role in wound-induced plant defense responses in tea plants.