Nanopriming with carbon dots enhances cotton seed germination and salt tolerance by activating salt-induced ROS signaling to modulate Na+ homeostasis

Soil salinity severely reduces agricultural productivity by impairing seed germination and plant growth, thereby threatening the sustainable development of eco-friendly farming worldwide. The utilization of seed nanopriming, specifically using carbon dots (CDs), alleviates the side effects of salt stress during seed germination in cotton (Gossypium hirsutum. L), but the underlying mechanisms remain poorly characterized. In this study, we investigated the impact of CDs priming on cotton seeds by assessing their physiological, biochemical, and transcriptomic responses under salinity stress. Nanopriming with CDs significantly increased seedling root length (205.2 %), germination rate (32 %) and seed vigor index (378.4 %) under salt stress compared with controls (water priming). CDs primed seeds showed significantly lower content of superoxide anion radicals (O2•−) and malondialdehyde (MDA) while hydrogen peroxide (H2O2) levels increased by 42.3 %–48.5 %. Under salt stress conditions, CDs priming also resulted in a significant reduction in Na+ accumulation (15.3 % lower than the control) without affecting K+ content. Further research found that the enhanced Na+ efflux and seed germination induced by CDs priming were substantially suppressed by an NADPH oxidase inhibitor, diphenyleneiodonium chloride (DPI). Thus, we confirmed that GhRboh-mediated H₂O₂ regulates Na+ homeostasis to promote seed germination under salinity. Transcriptome sequencing (RNA-Seq) results suggested that CDs priming-induced salt stress resistance is likely linked to oxidative stress response, MAPK signaling pathway, cellular ion homeostasis and Ca²⁺-binding proteins. Moreover, CDs priming treatment significantly upregulated the relative expression levels of GhRboh genes, Ca2+ influx genes and SOS1/NHX7. These results indicate that GhRboh-mediated H2O2 accumulation may modulate Na+ homeostasis via the Ca2+-dependent Na+/H+ antiporter system to increase salt tolerance in cotton seed. This study provides novel mechanistic insights into nanomaterial-based seed priming strategies for improving crop resilience in saline soils.