Conversion of lipids into carbohydrates rescues energy insufficiency in rapeseed germination under waterlogging stress.

Waterlogging stress, particularly during seed germination, significantly affects plant growth and development. However, the physiological and molecular mechanisms underlying waterlogging stress responses during rapeseed germination remain unclear. In this study, two rapeseed cultivars, Xiangzayou518 (waterlogging-sensitive) and Dadi199 (waterlogging-tolerant), were used to explore the physiological mechanisms underlying rapeseed response to waterlogging stress during germination. Our results showed that waterlogging significantly decreased the emergence percentage and seedling growth rate. During the radicle elongation period (from 48 to 96 h post-germination), the most sensitive period to waterlogging during germination, sugar content, and glycolysis efficiency were significantly decreased, but anaerobic fermentation was enhanced. In tolerant cultivars, when the energy supply was insufficient, the conversion efficiency of lipids into sugar increased, and the activities of isocitrate lyase, malate synthase, and fructose-1, 6-diphosphatase were enhanced by 11.63, 19.06, and 20.37%, respectively, at 72 h post-germination under waterlogging stress. Transcriptome data showed that the differentially expressed genes were significantly enriched in glucose and lipid metabolism pathways when comparing waterlogged stress and normal conditions. These results indicate that waterlogging affects seed germination in rapeseed by inhibiting carbohydrate metabolism, and the conversion capacity of lipids into sugar under waterlogging stress was stronger in tolerant cultivars than in sensitive cultivars, thus rescuing the insufficient energy supply in seed germination and seedling growth. This study reveals the physiological mechanism of rapeseed response to waterlogging stress during seed germination and provides a valuable reference for improving waterlogging tolerance.