Revealing boron-mediated salt stress alleviation in cotton by AsA-GSH cycle and transcriptomic analysis

Salt stress poses a substantial threat to the productivity of cotton (Gossypium hirsutum L.). Although previous studies have demonstrated that boron (B) can alleviate cotton salt stress by maintaining cell wall homeostasis or reducing ion toxicity, there is currently limited understanding on how B mitigates salt damage by regulating cotton antioxidant capacity, particularly through the ascorbic acid (AsA)-glutathione (GSH) cycle and how it modulates the AsA and GSH synthesis pathways. This study investigated the effects of B supply on the antioxidant system in cotton under salt stress through physiological and transcriptomic analysis. The results revealed that salt stress inhibited cotton growth, induced ionic and oxidative stress. The application of 200 μM B effectively alleviated salt damage and reduced ROS accumulation by increasing total flavonoids and AsA contents, and monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), glutathione peroxidase (GPX), and glutathione S-transferase (GST) activities. B also reduced Na ⁺ uptake to alleviate ion stress. Transcriptomics analysis showed that B promoted AsA synthesis by promoting the expression of GME, VTC2, VTC4, GalDH, and GalLDH in the GDP-mannitol synthesis pathway, while also regulating GGT, GGCT, GS, and γ-GCS in the GSH synthesis pathway to maintain the GSH homeostasis. Therefore, these results suggested that B-mediated regulation of the AsA-GSH cycle plays a crucial role in alleviating salt-induced oxidative stress in cotton. This study highlights the potential of B to enhance salt tolerance in cotton.