Zn-based seed priming enhances drought resistance during germination of Lespedeza potaninii: physiological and...

Lespedeza potaninii is a species of flowering plant in the legume family. Due to its strong stress tolerance and nitrogen-fixing capacity, Lespedeza potaninii has become a crucial plant species for reseeding and restoring degraded grasslands in China. However, drought stress during the seedling or germination stage severely impacts the effectiveness of Lespedeza potaninii-based grassland restoration efforts. To screen seed-soaking agents enhancing seed germination under sorbitol-simulated drought stress and explore the underlying mechanisms, seed germination, physiological parameters and transcriptomic regulation of Lespedeza potaninii seeds under different seed-soaking treatments were analyzed. The results revealed that sorbitol-simulated drought stress significantly reduced seed germination of Lespedeza potaninii. However, treatments with 0.04% ZnSO₄ or 0.10 mg/L ZnO-NPs could significantly enhance germination percentages. 0.04% ZnSO₄ and 0.10 mg/L ZnO-NPs treatments notably decreased hydrogen peroxide (H₂O₂) levels, with 0.10 mg/L ZnO-NPs also increasing glutathione cycle efficiency. Transcriptomic analysis revealed that a 0.10 mg/L ZnO-NPs treatment improved drought resistance by enhancing energy and nutrient metabolism, particularly nitrogen metabolism, which in turn strengthened antioxidant defenses through the glutathione metabolism. In contrast, the ZnSO₄ treatment promoted sulfur metabolism, thereby enhancing glutathione metabolism and increasing the biosynthesis of flavonoids and monoterpenes, further improving drought resistance. Both treatments likely involve zinc ions in promoting antioxidant synthesis and maintaining cell membrane stability by regulating antioxidant defense, particularly glutathione metabolism. These findings offer novel insights and strategies for improving seed emergence and establishment in degraded grasslands.