Changes in defense-related enzymes and phenolics in resistant and susceptible common wheat cultivars under aphid stress

The cereal aphids Rhopalosiphum padi L. are serious pests on grain crops, reducing the quality and yield by direct feeding damage and virus transmission. The changes in the physiological and biochemical parameters of two wheat cultivars under aphid stress were investigated to understand aphid-resistance mechanisms. The activity levels of phenylalanine ammonia-lyase (PAL), peroxidase (POD), tyrosine ammonia-lyase (TAL), Ca2+-ATPase and Mg2+-ATPase in resistant cultivar W0923 increased during aphid feeding, and most of them were significantly higher than those in the susceptible cultivar GN21. However, these enzyme activities increased and then decreased in GN21. The polyphenol oxidase (PPO) activity in W0923 was maintained longer than in GN21. The total phenol contents of the two cultivars exhibited significant increases on the 15th day compared with the untreated controls, and the content in W0923 was significantly higher than in GN21 by the 30th day. Most of the POD, PPO, PAL, TAL and Ca2+-ATPase activities and phenolic metabolite contents were higher in W0923 than in GN21 under the untreated control conditions. The Ca2+-ATPase and PAL activities positively correlated with POD, PPO and Mg2+-ATPase activities. Ca2+-ATPase and PAL may be key biochemical markers for evaluating aphid resistance. W0923 had a strong ability to maintain higher enzyme activities and synthesize more phenols and tannins than GN21, which contributed to aphid resistance.