Regulatory Mechanisms of Exogenous ABA and NDGA on Photosynthetic and Antioxidant Physiology in Waterlogging-Stressed Brassica napus L.

The seedling stage is a critical period for the morphological development of rapeseed, and waterlogging stress seriously affects yield and rapeseed quality. Reasonable use of plant growth regulators can increase crop yield, improve quality, and enhance crop stress tolerance. ABA is an important signaling molecular for stress response, and play key role in enhancing plant stress tolerance. Two Brassica napus varieties with different waterlogging tolerance were used materials to investigate the effects and physiological mechanisms of ABA and its inhibitor NDGA in regulating waterlogging tolerance. The results indicated that waterlogging significantly inhibited the growth of rapeseed, leading to lower plant height, root length, biomass, leaves yellowing and shedding, and a higher MDA and reactive oxygen species (H ₂ O ₂ , O ₂ ⁻) content. The results of phenotypic observation and waterlogging tolerance coefficient indicated that ABA treatment before waterlogging stress improved the waterlogging tolerance of rapeseed, but NDGA treatment exacerbated the waterlogging damage and increased plant mortality rate. NDGA treatment resulted in more stomatal closure in waterlogging sensitive ZS6 compared to waterlogging tolerant rapeseed HYZ50 during waterlogging stress. However, there is no significant difference in the effect of ABA treatment on stomatal behavior of rapeseed with different waterlogging tolerance. For the two lines treated with ABA or NDGA before waterlogging, there were significant differences in the degree of membrane lipid peroxidation, photosynthetic pigment content, antioxidant activity, osmotic regulation substance content, and ROS metabolite content. HYZ50 showed better physiological response to waterlogging than that of ZS6, with stronger antioxidant capacity (POD, CAT activity) and osmotic regulation (proline, soluble sugar accumulation). The correlation analysis between the waterlogging tolerance index (WTI) and growth and physiological indicators revealed WTI was significant negative correlation with MDA content, POD activity, H ₂ O ₂ and O ₂ ⁻ content, but positive correlation with CAT activity, underground fresh weight, root vitality, plant height, root length, number of green leaves, aboveground fresh weight, aboveground dry weight, and underground dry weight and WTI. Principal component analysis and waterlogging tolerance index analysis found that ABA treatment before waterlogging stress improved the waterlogging tolerance of rapeseed, while NDGA treatment exacerbated the waterlogging damage. This study systematically investigated the role of ABA treatment before waterlogging in alleviating waterlogging damage, laying the foundation for green and efficient cultivation of rapeseed.