Melatonin induces resistance against Penicillium expansum in apple fruit through enhancing phenylpropanoid metabolism

Apple fruit is delicious fruit with great economic value. However, harvested apples are susceptible to the infection of Penicillium expansum, which results in quality degradation. ‘Golden Delicious’ apples were dipped with melatonin solution to investigate its influence on blue mold and the dynamic changes of the major metabolites contents and enzymes activities in phenylpropanoid metabolism. Melatonin markedly suppressed lesion development of P. expansum -inoculated apple fruit. Melatonin dipping also distinctly improved 4-coumarate coenzyme A ligase, cinnamic acid 4-hydroxylase, phenylalanine ammonia lyase, polyphenol oxidase, laccase, glucose-6-phosphate dehydrogenase, and glucose phosphate isomerase activities. Moreover, p-coumaric acid, total phenolic compounds, ferulic acid, flavonoids, erucic acid, caffeic acid, lignin, phenylalanine, tyrosine, and tryptophan contents were also enhanced by melatonin. All these findings indicate that melatonin treatment activates the key enzyme activity in phenylpropanoid metabolism to accelerate metabolites accumulation in apples, therefore inducing resistance to blue mold.