Coupled Metabolome With Physiology Unveiled Mechanisms for Cadmium Affecting Active Ingredients Synthesis in Salvia Miltiorrhiza, A Non-cd-hyperaccumulator
Abstract BackgroundCadmium (Cd) poses threats to human health by affecting the safety (Cd accumulation) and quantity (contents of active ingredients) of Salvia miltiorrhiza due to human activities and Cd characteristics. It remains largely unknown how Cd stress affects the synthesis of active ingredients in S. miltiorrhiza. ResultsHere we investigated physiologies (contents of Cd, malondialdehyde (MDA) and proline, and activities of superoxide dismutase, peroxidase (POD) and catalase (CAT)), transfer factor (TF), bioconcentration factor (BCF) and metabolites of S. miltiorrhiza at different levels of Cd contamination with a pot experiment. The results revealed that Cd concentration, as it rose in soil, increased significantly in roots and leaves with TFs and BCFs below 1 in the Cd addition groups; POD and CAT activities and proline content increased and then declined significantly. Besides, amino acids and organic acids (especially D-glutamine (D-Gln), L-aspartic acid (L-Asp), L-phenylalanine (L-Phe), L-tyrosine (L-Try), geranylgeranyl-PP (GGPP), and rosmarinic acid (RA)) contributed more than other metabolites in discriminating roots under different levels of Cd contamination. With Cd concentration rising, the relative content of GGPP declined and then increased significantly; RA content rose significantly; content of L-Phe and L-Try increased and then declined significantly, while the content of D-Gln and L-Try decreased and then increased significantly. Conclusions These results suggested that S. miltiorrhiza belonged to a non-Cd-hyperaccumulator with most Cd accumulated in roots; Cd enhanced the RA synthesis via regulating amino acid metabolism but inhibited the tanshinone synthesis mainly by declining the GGPP content, with proline, POD and CAT playing vital roles in resisting Cd stress.