Introduction: Salt stress has emerged as a predominant abiotic factor that jeopardizes global crop growth and yield. The plant hormone salicylic acid (SA) has notable potential in mitigating salt toxicity, yet its mechanism in enhancing the salinity tolerance of tobacco plants is not well explored.Methods: This study aimed to assess the potential benefits of exogenous SA application (1.0 mM) on tobacco seedlings subjected to saline soil conditions.Results: The foliar spray of SA partially mitigated these salt-induced effects, as evidenced by a reduction of malondialdehyde content, and improvements of leaf K⁺/Na⁺ ratios, pigment biosynthesis, and electron transport efficiency under NaCl stress. Additionally, SA increased the contents of total phenolic compound and soluble protein by 16.2% and 28.7% to alleviate NaCl-induced oxidative damage. Under salt stressed conditions, the activities of antioxidant enzymes, including superoxide dismutase, ascorbate peroxidase, catalase, and peroxidase increased by 4.2%~14.4% in SA sprayed tobacco seedlings. Exogenous SA also increased ascorbate and glutathione levels and reduced their reduced forms by increasing the activities of glutathione reductase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase. qRT−PCR analysis revealed that the key genes regulating SA biosynthesis, carbon assimilation, the antioxidant system and the ascorbate−glutathione cycle were activated by SA under conditions of salt stress.Discussion: Our study elucidates the physiological and molecular mechanisms of exogenous SA in enhancing plant salt tolerance and provides a practical basis for crop improvement in saline environments.

Introduction: Drought stress, exacerbated by global climate change, poses a significant threat to agricultural productivity and global food security. Plants have evolved intricate adaptive mechanisms, with the root system playing a crucial role in sensing soil water deficits and acquiring essential resources. Methods: This study investigated the time-course adaptation strategies of two Nicotiana tabacum varieties, ZC208 (drought-tolerant) and ZY100 (drought-sensitive), to different levels of drought stress through altered root system architecture (RSA) and transcriptomic regulations. Results: RSA parameters generally decreased, while specific root length, surface area, and volume increased. Antioxidant enzyme activities (SOD, POD, CAT) and proline content in roots significantly increased, contrasting with a reduction in soluble sugars. This research provides valuable insights into the dynamic molecular and physiological mechanisms underlying drought adaptation in tobacco roots, offering potential targets for breeding drought-tolerant cultivars to enhance agricultural resilience in a changing climate. Analysis of the root transcriptome identified a large cohort of differentially expressed genes (DEGs), with more downregulated than upregulated DEGs across all drought stages in both varieties. Time-course analysis using STEM identified distinct expression profiles for ZC208 (6 profiles) and ZY100 (8 profiles), highlighting dynamic gene regulation over time. WGCNA identified modules strongly correlated with RSA parameters, with key pathways including ‘MAPK signaling pathway, plant’, ‘plant-pathogen interaction’, and ‘sesquiterpenoid and triterpenoid biosynthesis’. Genes involved in plant hormone signaling (e.g., AUX/IAA, PYR/PYL) and starch/sucrose metabolism (e.g., endoglucanase, β-glucosidase) showed differential expression patterns, indicating their crucial roles in drought response. Discussion: This research provides valuable insights into the dynamic molecular and physiological mechanisms underlying drought adaptation in tobacco roots, offering potential targets for breeding drought-tolerant cultivars to enhance agricultural resilience in a changing climate.