Abstract:

Soil salinization is a significant factor that limits plant nutrient uptake and affects plant growth and development. Sainfoin （Onobrychis viciifolia） is a native fabaceae species in saline-alkali regions of China， and exogenous abscisic acid （ABA） plays a positive regulatory role in enhancing plant stress resistance. This study investigates the effects of exogenous ABA on the growth and physiological characteristics of sainfoin seedlings subjected to salt stress. Using a nutrient solution sand culture method， various concentrations of ABA were sprayed on the leaves of both salt-tolerant （‘GH’， ‘GN’， ‘1994’） and salt-sensitive （‘10295’， ‘2323-2’， ‘2668’） sainfoin seedlings under a 0.8% NaCl treatment. Specifically， one control group （CK） and four treatment groups were established： 0.8% NaCl （T₁）， 0.8% NaCl+0.1 mmol·L^-1 ABA （T₂）， 0.8% NaCl+0.2 mmol·L^-1 ABA （T₃） and 0.8% NaCl+0.3 mmol·L^-1 ABA （T₄）. The optimal concentration of ABA for alleviating salt stress was identified. The results indicate that ABA has a mitigating effect on salt stress. That plant height， leaf area， aboveground biomass， underground biomass， relative leaf water contents， root activity， K⁺ contents， gibberellin contents in leaves and roots， zeatin contents in leaves and roots and auxin （IAA） contents in leaves decreased with increasing salt stress. The changes in the salt-tolerant material ‘GH’ were quite significant. The plant height increased by 20.48%， while the leaf area increased by 4.63%； Additionally， the aboveground biomass saw an increase of 26.75%， and the underground biomass increased significantly by 56.66%； The relative leaf water content rose by 28.19%， and root activity experienced a substantial increase of 65.41%. Furthermore， K⁺ content increased by 24.36%， leaf gibberellin content rose by 47.55%， and root gibberellin content increased by 36.05%； The leaf zeatin content increased by 24.39%， while leaf zeatin saw a notable rise of 80.53%， and leaf IAA content increased by 19.20%， respectively， in 0.8% NaCl， compared to control. Additionally， malonaldehyde contents， superoxide dismutase activity， peroxidase activity， catalase activity， Na⁺ contents， Ca²⁺ contents， ABA contents in leaves and roots and IAA contents in roots were reduced in response to salt. The changes in the salt-sensitive material ‘10295’ were relatively insignificant， with malonaldehyde contents， superoxide dismutase activity， peroxidase activity， catalase activity， Na⁺ contents， Ca²⁺ contents， ABA contents in leaves， ABA contents in roots and IAA contents in roots increasing by 14.91%， 18.64%， 26.15%， 10.08%， 24.47%， 30.24%， 8.72%， 27.64%， and 30.87%， respectively， in 0.8% NaCl stress. These results indicate that exogenous ABA can mitigate oxidative damage to cells caused by salt stress， maintaining the integrity of the cell membrane system and cell osmotic pressure. In this study， 0.2 mmol·L^-1 ABA demonstrated the most effective results， with a more pronounced response observed in salt-tolerant materials compared to salt-sensitive materials.

Key words: sainfoin, salt stress, abscisic acid, endogenous hormones