Differential response of proline metabolism defense, Na+ absorption and deposition to salt stress in salt‐tolerant and salt‐sensitive rapeseed (Brassica napus L.) genotypes

Soil salinization is a major abiotic factor threatening rapeseed yields and quality worldwide, yet the adaptive mechanisms underlying salt resistance in rapeseed are not clear. Therefore, this study aimed to explore the differences in growth potential, sodium (Na⁺) retention in different plant tissues, and transport patterns between salt-tolerant (HY9) and salt-sensitive (XY15) rapeseed genotypes, which cultivated in Hoagland's nutrient solution in either the with or without of 150 mM NaCl stress. The results showed that the inhibition of growth-related parameters of the XY15 genotype was higher than those of the HY9 in response to salt stress. The XY15 had lower photosynthesis, chloroplast disintegration, and pigment content but higher oxidative damage than the HY9. Under NaCl treatment, the proline content in the root of HY9 variety increased by 8.47-fold, surpassing XY15 (5.41-fold). Under salt stress, the HY9 maintained lower Na⁺ content, while higher K⁺ content and exhibited a relatively abundant K⁺/Na⁺ ratio in root and leaf. HY9 also had lower Na⁺ absorption, Na⁺ concentration in xylem sap, and Na⁺ transfer factor than XY15. Moreover, more Na⁺ contents were accumulated in the root cell wall of HY9 with higher pectin content and pectin methylesterase (PME) activity than XY15. Collectively, our results showed that salt-tolerant varieties absorbed lower Na⁺ and retained more Na⁺ in the root cell wall (carboxyl group in pectin) to avoid leaf salt toxicity and induced higher proline accumulation as a defense and antioxidant system, resulting in higher resistance to salt stress, which provides the theoretical basis for screening salt resistant cultivars.