Physiological and metabolic responses of Sophora tonkinensis to cadmium stress.

Sophora tonkinensis is a significant medicinal plant indigenous to China and Vietnam. In China, S. tonkinensis is mainly grown naturally on limestone mountains or is cultivated artificially in arable land. Heavy metal contamination in agricultural soil, particularly cadmium (Cd), poses serious threats to soil health, as well as the growth and productivity of S. tonkinensis. However, information regarding the physiological and metabolic mechanism of S. tonkinensis under Cd toxicity conditions remains limited. In this study, a hydroponic experiment was conducted to investigate the physiological and metabolic responses of S. tonkinensis to varying concentrations of Cd (0, 20, 40, 60, 80 μM), designated as T0, T1, T2, T3, and T4 respectively. The results indicated that the Cd stress significantly impaired the growth and physiological activity of S. tonkinensis. Specifically, reductions were observed in plant height (15.3% to 37.1%) along with shoot fresh weight (9.6% to 36.3%), shoot dry weight (8.2% to 34.1%), root fresh weight (6.7% to 38.2%) and root dry weight (5.1% to 51.3%). This impairment was attributed to a higher uptake and accumulation of Cd in the roots. The decrease in growth was closely linked to the increased production of reactive oxygen species (ROS), which led to cellular damage under Cd toxicity; however, increased antioxidant enzyme activities improved the stress tolerance of S. tonkinensis's stress to Cd toxicity. Non-targeted metabolomic analyses identified 380 differential metabolites (DMs) in the roots of S. tonkinensis subjected to varying level of Cd stress, including amino acids, organic acids, fatty acids, ketones, and others compounds. Further KEGG pathway enrichment analysis revealed that several pathways, such as ABC transporters, isoflavonoid biosynthesis, and pyrimidine metabolism were involved in the response to Cd. Notably, the isoflavonoid biosynthesis pathway was significantly enriched in both T0 vs. T2 and T0 vs. the higher level (80 μM) of Cd stress, highlighting its significance in the plant responses to Cd stress. In conclusion, the identification of key pathways and metabolites is crucial for understanding Cd stress tolerance in S. tonkinensis.

Supplementary information: The online version contains supplementary material available at 10.1007/s12298-024-01522-w.