Novel Quantitative Metabolomic Approach for the Study of Stress Responses of Plant Root Metabolism

Quantitative metabolomics (qMetabolomics) is a powerful tool for understanding the intricate metabolic processes involved in plant abiotic stress responses. qMetabolomics is hindered by the limited coverage and high cost of isotopically labeled standards. In this study, we first selected 271 metabolites which might play important roles in abiotic stress responses as the targets and established a comprehensive LC–MS/MS based qMetabolomic method. We then developed a novel metabolic labeling method using <i>E. coli</i>–<i>Saccharomyces cerevisiae</i> two-step cultivation for the production of uniformly <sup>13</sup>C-labeled metabolites as internal standards. Finally, we applied the developed qMetabolomic method to investigate the influence of Pb stress on maize root metabolism. The absolute concentration of 226 metabolites in maize roots was accurately quantified in a single run within 30 min. Our study also revealed that glycolysis, purine, pyrimidine, and phospholipids were the main metabolic pathways in maize roots involved in Pb stress response. To our knowledge, this is the most comprehensive qMetabolomic method for plant metabolomics thus far. We developed a simple and inexpensive metabolic labeling method which dramatically expanded the availability of uniformly <sup>13</sup>C labeled metabolites. Our findings also provided new insights of maize metabolic responses to Pb stress.