茉莉酸对棉花单宁含量和抗虫相关酶活性的诱导效应

以植物生长调节物茉莉酸(Jasmonic acid,JA)为诱导子,以常规棉为研究对象,探讨了外源茉莉酸对棉花幼苗单宁和蛋白酶抑制素以及其它抗虫相关酶活性诱导的浓度依赖性和持久性,讨论了棉花抗虫相关物质的抗虫效果.结果表明,0.01、0.1和1.0 mmol/L茉莉酸都能在2周内诱导棉花单宁和胰蛋白酶抑制素(Proteinase inhibitors,PIs)含量增加,诱导多酚氧化酶(Polyphenol oxidase,PPO)、苯丙氨酸解氨酶(Phenylalanine ammonia-lyase,PAL)、过氧化物酶(Peroxidase,POD)和过氧化氢酶(Catalase,CAT)活性升高.对3种浓度茉莉酸的诱导效应进行分析表明,0.1 mmol/L茉莉酸对于诱导PIs、PPO、POD和CAT最有效,0.1和1.0 mmol/L茉莉酸对于诱导棉花单宁和苯丙氨酸解氨酶等效,二者的诱导效应均高于0.01 mmol/L.对茉莉酸诱导抗性的持久性进行分析表明,最佳诱导效应发生的时间各不相同:POD活性在JA处理后第1天最高,随后呈下降趋势,PIs和单宁含量分别在JA处理后第7天和第14天达最大值；JA处理后第1天和第7天的PPO活性无明显差异,但明显高于第14天；JA处理后第7天和第14天的PAL活性无明显差异,但明显高于第1天；JA处理后第1、7和14天棉花叶片的CAT活性均无明显差异.以上结果表明,茉莉酸可通过增加棉叶单宁和PIs含量、提高棉叶PAL、PPO、POD和CAT活性等增强棉花幼苗的抗虫性.

Induction effects of jasmonic acid on tannin content and defense-related enzyme activities in conventional cotton plants

Cotton (Gossypium hirsutum L.) is an important crop worldwide challenged by a number of pests which cause enormous yield loss. Although extensive cultivation of transgenic Bt cotton has decreased the population growth of the most destructive pest, cotton bollworm (Helicoverpa armigera), the secondary pest like mirid bug has become a primary pest. In addition to the evolution of Bt toxin resistance in cotton bollworm, it is urgent to develop environment friendly and plant-derived pesticides for the integrated pest management. Induction of plant defense against pests is very common among higher plants. Jasmonic acid (JA) is a kind of plant growth regulator with a variety of biological function except for induced plant defense against herbivores. The objectives of the current study were to investigate the dosage- and exposure time-dependent induction of defense-related secondary metabolites and antinutritive/antidigestive enzymes in cotton seedlings by exogenous application of JA. The potential pest control nature of induced defense in seedlings of conventional cotton plants by JA was also discussed in terms of the fecundity, developmental time, mortality and parasitism of insects. We hypothesized that, as a ubiquitous phytohormone, JA should regulate the induced plant defense in cotton like those in some model plants including mustard, tobacco and tomato by increasing the contents of some feeding deterrent secondary metabolites and the activity of enzymes responsible for their synthesis, as well as the activities of antinutritive and antidigestive enzymes. Results of the present study suggested that 0.01 mmol/L, 0.1 mmol/L, and 1.0 mmol/L JA were effective concentrations in priming the pest resistance nature of six-foliage cotton seedlings within two weeks in terms of enhanced contents of cotton tannin and protease inhibitors (PIs) and increased activities of phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) and catalase (CAT). In comparison, 0.1 mmol/L jasmonic acid was more effective in inducing PIs, PPO, POD and CAT than the other two concentrations tested, while 0.1 mmol/L and 1.0 mmol/L JA were equally powerful in priming tannin and PAL, and both JA concentrations were more effective than 0.01 mmol/L JA. We also found that JA concentration, time after JA exposure and their interaction have significant effects on tannin content, PPO activity and POD activity, and that JA concentration and time after JA exposure have significant effect on PIs content and PAL activity, while JA concentration and its interaction with exposure time after JA exposure have significant effects on CAT activity. In addition, analysis of the duration of JA-mediated defense suggested that the optimal induction effects occurred one day after JA treatment for POD, 7 d for PIs, 14 d for tannin, 1 d and 7 d for PPO, 7 d and 14 d for PAL, while no significance was observed for CAT. In summary, JA can enhance cotton defense against insects by the induction of defense-related chemicals like tannin, some antinutritive/antidigestive enzymes like PPO, POD, CAT, and enzyme related to the synthesis of tannin like PAL. Future work should focus on the real effects of induced defense against insects in terms of the feeding behavior, oviposition preference, ecological immunity, detoxification capacity, and tritrophic interaction among cotton plant, herbivore insects and natural enemies, thereby facilitating the discovery of the physiological, ecological and biochemical basis of JA-induced plant defense.