Comparative metabolomics analysis of tolerant and sensitive genotypes of rapeseed (Brassica napus L.) seedlings under drought stress

Drought stress is a major abiotic stress that poses serious threats to the yield and quality of rapeseed. Understanding the mechanisms underlying the drought tolerance of rapeseed is of great importance for the breeding of drought-resistant rapeseed varieties. Here, we compared the phenotypic characteristics, photosynthetic physiology, specific metabolites and related metabolic pathways between the drought-tolerant genotype (Q2) and drought-sensitive genotype (Q8) of rapeseed under drought stress using gas chromatography and liquid chromatography–mass spectrometry. The results indicated that drought stress decreased the total biomass and photosynthesis of both genotypes, particularly those of Q8, and the reduction was substantially lower in the root surface area, root volume and root diameter of Q2 than in those of Q8 under drought stress. The adverse effect on Q2 could be improved by increasing the specific leaf area, root length, and non-photochemical quenching. Furthermore, four metabolic pathways (galactose metabolism, TCA cycle, aminoacyl-tRNA biosynthesis as well as nicotinate and nicotinamide metabolisms) were greatly activated in Q2 compared with those in Q8 under drought stress. Metabolic profiling revealed 17 differential metabolites between the two genotypes, including carbohydrates, amino acids and organic acids and the increase in tagatose was accompanied by the accumulation of fumaric acid in the roots of Q2 under drought stress. The drought resistance of Q2 could be attributed to the accumulation of more metabolites, such as galactose, tagatose, glycerone and fumaric acid. Our results provide valuable insights into the growth characteristics, physiological changes and metabolic regulation mechanism of rapeseed under drought stress as well as a theoretical basis for the breeding of drought-resistant rapeseed varieties.