Abstract The hemibiotrophic oomycetes are significant threats to a wide range of Cucurbitaceae species, causing substantial losses of plant productions. Particularly, Phytophthora melonis Katsura evokes severe symptoms, thus dramatically limiting the yield in cucumber. However, the information about cucumber–P. melonis interaction is still limited. This study explored the changes in the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POX), catalase (CAT), superoxide dismutase (SOD) and polyphenol oxidase (PPO) in cucumber roots of two resistant genotypes (Soheil and Ramezz), one moderately resistant genotype (Baby) and three highly susceptible genotypes (Extrem, Mini 6–23 and Yalda), over the time courses of 7, 14 and 21 days after inoculation (DAI). The results indicated that the activities of defense-related enzymes differed between the resistant and highly susceptible genotypes. Although the defense-related enzymatic activities were elevated sharply in the resistant and moderately resistant genotypes after inoculation, no significant correlations were present between the activity trends of PPO, SOD and CAT and resistance characteristics. Moreover, no significant changes in enzyme activities were found in the control plants, non-inoculated plants of the six genotypes during the testing period. Altogether, the resistance of cucumber to P. melonis is related to POX and PAL activities, but does not show relationship with PPO, SOD and CAT activities. Studying the physiological metabolic pathways of POX and PAL appears to be an important direction in research to elucidate the resistance to P. melonis in cucumber genotypes.

中文翻译：

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与冬瓜疫霉宿主特异性抗病性相关的新型黄瓜酶

摘要 半生物营养型卵菌是对葫芦科多种物种的重大威胁，造成植物生产的重大损失。尤其是甜瓜疫霉引起严重的症状，从而极大地限制了黄瓜的产量。然而，关于黄瓜-P的信息。甜瓜的互动仍然有限。本研究探讨了两种抗性基因型（Soheil和Ramezz）黄瓜根中苯丙氨酸解氨酶（PAL）、过氧化物酶（POX）、过氧化氢酶（CAT）、超氧化物歧化酶（SOD）和多酚氧化酶（PPO）活性的变化，一种中等抗性基因型（Baby）和三种高度敏感基因型（Extrem、Mini 6-23 和 Yalda），在接种后 7、14 和 21 天的时间过程中（DAI）。结果表明，防御相关酶的活性在抗性和高度易感基因型之间存在差异。尽管接种后抗性和中抗性基因型的防御相关酶活性急剧升高，但 PPO、SOD 和 CAT 的活性趋势与抗性特征之间不存在显着相关性。此外，在测试期间，在六种基因型的对照植物、未接种植物中未发现酶活性的显着变化。综上所述，黄瓜对 P. melonis 的抗性与 POX 和 PAL 活性有关，与 PPO、SOD 和 CAT 活性无关。研究 POX 和 PAL 的生理代谢途径似乎是阐明 POX 抗性研究的一个重要方向。