Sowing Methods and Strigolactones Alleviate Damage to the Photosynthetic System of Rice Seedlings Under Salt Stress by Enhancing Antioxidant Capacity

Seedling cultivation of rice (<i>Oryza sativa</i> L.) is a critical initial step in rice production. This study investigated the effects of sowing methods and strigolactone (GR24) on rice seedlings under salt stress. Results showed that drill-sown seedlings exhibited superior quality under normal conditions compared to broadcast-sown seedlings. Salt stress significantly increased the contents of Cl^-, Na⁺, reactive oxygen species (ROS), and malondialdehyde (MDA), disrupted chloroplast structure and hormonal balance, and reduced gas exchange parameters and chlorophyll fluorescence parameters. Notably, drill-sowing conferred stronger salt tolerance than broadcast-sowing. Exogenous application of GR24 enhanced activities of antioxidant enzymes-including superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT)-and elevated non-enzymatic antioxidant contents such as ascorbic acid (ASA), glutathione (GSH), total phenolics, and flavonoids, alongside related enzyme activities. Concurrently, GR24 reduced Na⁺ and Cl^- accumulation, lowered the Na⁺/K⁺ ratio, and increased the contents of K⁺, Ca²⁺, Mg²⁺, and hormones. Consequently, GR24 decreased MDA and ROS levels, protected membrane integrity, reduced electrolyte leakage, repaired chloroplast structure, and improved gas exchange and chlorophyll fluorescence parameters. Due to their superior spatial distribution and photosynthetic efficiency, drill-sown seedlings synergized with GR24 to enhance antioxidant capacity under salt stress, enabling more effective scavenging of peroxidative radicals, stabilization of the photosynthetic system, and mitigation of salt-induced growth inhibition. Ultimately, this combination demonstrated greater stress alleviation than broadcast-sown seedlings.