Metabolite Profiling of the Response of Burdock Roots to Copper Stress

Arctium lappa L. (Asteraceae), also known as burdock, has a long history of cultivation as a dietary vegetable worldwide. Stress in plants disrupts metabolic homeostasis and requires adjustment of metabolic pathways. Exposure to heavy metals is one of the most prevalent environmental stresses encountered by plants. In this study, metabolite profiling based on H-1 NMR and GC-MS was used to obtain a holistic view of the response of burdock roots to copper stress. The principal component analysis model generated from the NMR data showed significant separation between groups. Copper-treated burdock roots were characterized by increased levels of phenols and decreased levels of primary metabolites. These results suggest that copper stress leads to activation of the phenylpropanoid pathway and growth inhibition. GC-MS analyses revealed increased levels of unsaturated fatty acids and decreased levels of sterols in the copper-treated group. Changes in metabolite concentrations were analyzed by UPLC/QTRAP-MS, and the significances were confirmed by two-way analysis of variance and Bonferronis test. Interestingly, linoleic acid was increased about 2.7-fold, from 316 +/- 64.5 to 855 +/- 111 ppm, in the group treated with copper for 6 days. This study demonstrates that metabolomic profiling is an effective analytical approach to understanding the metabolic pathway(s) associated with copper stress in burdock roots.