Metabolomic analysis with GC-MS to reveal potential metabolites and biological pathways involved in Pb & Cd stress response of radish roots

The radish (Raphanus sativus L.) is an important root vegetable crop. In this study, the metabolite profiling analysis of radish roots exposed to lead (Pb) and cadmium (Cd) stresses has been performed using gas chromatography-mass spectrometry (GC-MS). The score plots of principal component analysis (PCA) and partial least squares-discriminate analysis (PLS-DA) showed clear discrimination between control and Pb- or Cd-treated samples. The metabolic profiling indicated Pb or Cd stress could cause large metabolite alteration mainly on sugars, amino acids and organic acids. Furthermore, an integrated analysis of the effects of Pb or Cd stress was performed on the levels of metabolites and gene transcripts from our previous transcriptome work in radish roots. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of integration data demonstrated that exposure of radish to Pb stress resulted in profound biochemical changes including carbohydrate metabolism, energy metabolism and glutathione metabolism, while the treatment of Cd stress caused significant variations in energy production, amino acid metabolism and oxidative phosphorylation-related pathways. These results would facilitate further dissection of the mechanisms of heavy metal (HM) accumulation/tolerance in plants and the effective management of HM contamination in vegetable crops by genetic manipulation.