The study of physiological response mechanism and metabolomics on B. chinensis under drought

Background Drought has become an increasingly important environmental problem worldwide and is one of the major abiotic stress factors affecting crop growth and development. Therefore, elucidating the mechanism of drought resistance in plants is of great significance to improve the drought resistance of plants and to cultivate drought-resistant varieties. B. chinensis is an important medicinal plant and garden plant in China, and drought is one of the factors limiting the growth of B. chinensis, so it has become a research hotspot to investigate the physiological response mechanism of B. chinensis to drought. Results In this study, we investigated the physiological and biochemical response mechanisms of the root system of B. chinensis using B. chinensis seedlings as experimental materials, and conducted metabolomics analysis of the root system of B. chinensis using liquid chromatography-mass spectrometry (LC-MS) to verify the mechanisms of B. chinensis in response to drought stress after 0, 7, 14, 21, 28 d of drought and after re-watering.The results showed that: (1) with the prolongation of drought stress, the relative water content gradually decreased, the diameter of root, the diameter of the mid-column, the thickness of the cortex, and the diameter of the xylem all showed an upward trend and then a downward trend, the root activity gradually declined, the root structure was impaired, the cortex was not arranged and ruptured. (2) With the prolongation of drought stress, the cell membrane function was impaired, the relative conductivity and malondialdehyde content of roots tended to increase, the content of osmoregulatory substances such as soluble proteins and free proline also accumulated in large quantities in the roots, and the content of hydrogen peroxide and superoxide anion gradually increased. Meanwhile, the activities of peroxidase, catalase, glutathione reductase, ascorbate peroxidase and monodehydroascorbate reductase in the roots reached the maximum value after 28 d of drought, and all of them recovered to a different extent after re-watering. (3) A total of 656 differential metabolites were screened in the root system of B. chinensis under drought stress. In addition, KEGG enrichment analysis revealed that the metabolic pathways involved in the differential metabolites were mainly glycerophospholipid metabolism, sphingolipid metabolism, amino acid metabolism, tyrosine metabolism, arachidonic acid metabolism, flavonoid biosynthesis, steroid biosynthesis and tyrosine metabolism. Among them, the differences in flavonoid biosynthesis varied greatly, suggesting that flavonoids play an important role in the response to drought stress in B. chinensis. (4) The weighted gene co-expression network analysis WGCNA revealed high correlations between the three metabolite modules and root growth parameters and physiological and biochemical index parameters. Among them, the Meblue module was positively correlated with root activity, the Megreen module was positively correlated with catalase, and the Meturquoise module was positively correlated with malondialdehyde, catalase, soluble proteins, and relative conductivity. Conclusions This study reveals the defense response mechanism of B. chinensis under drought, and also analyzes the differential metabolites of B. chinensis under drought stress according to the changes in the quantity of related metabolites and explores the key metabolic pathways related to drought resistance, with a view to laying a theoretical foundation for physiological and metabolic studies revealing B. chinensis response to drought stress.