Metabolic response of Citrus limon to Asian citrus psyllid infestation revealed by EESI-MS and HPLC.

Asian citrus psyllid (ACP) causes direct and indirect damage to the citrus industry. Extractive electrospray ionization mass spectrometry (EESI-MS) and high performance liquid chromatography (HPLC) were used to detect the metabolites of C. limon leaves at 0, 12, 24, and 72 h after ACP treatment. The EESI-MS results showed that ACP infestation significantly affected metabolites within a short feeding duration with 8 metabolites identified. The metabolites in leaves of these four groups could be distinguished, with 55 peaks showing significant differences including methyl N-methylanthranilate, caffeic acid, and syringic acid. The quantification of 15 phenolic compounds with HPLC-UV method in C. limon leaves after ACP infestation showed that the total content of them reached a peak of 3504.69 μg g-1 at 12 h, with 9 phenolic compounds changing significantly (P < 0.05). A total of 21 metabolites identified in this study were involved in the biosynthesis pathways of flavonoid, flavone and flavonol, isoflavonoid and phenylpropanoid, and the degradation of aminobenzoate. Contents of epicatechin and caffeic acid increased with the feeding time of ACP as detected by both EESI-MS and HPLC. This may be related to plant defense. This study provides novel insights into the biochemical relationship of ACP and its host plants.