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.

中文翻译：

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干旱胁迫下油菜幼苗耐受和敏感基因型的比较代谢组学分析

干旱胁迫是一种主要的非生物胁迫，对油菜籽的产量和品质构成严重威胁。了解油菜籽耐旱机制对于抗旱油菜品种选育具有重要意义。在此，我们利用气相色谱和液相色谱-质谱联用技术比较了干旱胁迫下油菜耐旱基因型（Q2）和干旱敏感基因型（Q8）的表型特征、光合生理、特异性代谢产物和相关代谢途径。结果表明，干旱胁迫均降低了两个基因型的总生物量和光合作用，尤其是Q8，且干旱胁迫下Q2的根表面积、根体积和根直径的降低幅度明显低于Q8。对Q2的不利影响可以通过增加比叶面积、根长和非光化学猝灭来改善。此外，与Q8相比，干旱胁迫下Q2的四种代谢途径（半乳糖代谢、TCA循环、氨酰-tRNA生物合成以及烟酸和烟酰胺代谢）显着激活。代谢分析揭示了两种基因型之间的 17 种差异代谢物，包括碳水化合物、氨基酸和有机酸，并且塔格糖的增加伴随着干旱胁迫下 Q2 根部富马酸的积累。 Q2的抗旱性可能归因于更多代谢物的积累，如半乳糖、塔格糖、甘油和富马酸。该研究结果为揭示干旱胁迫下油菜生长特性、生理变化和代谢调控机制提供了有价值的见解，也为抗旱油菜品种选育提供了理论依据。