Integrative analysis of salt stress responses in peanut, sunflower, and soybean seedlings reveals tissue-specific tolerance mechanisms

Salt stress severely restricts oilseed crop productivity, underscoring the need for species-specific insights into tolerance mechanisms. In this study, 21 sunflower ( Helianthus annuus ), 20 peanut ( Arachis hypogaea ), and 43 soybean ( Glycine max ) tolerant and sensitive cultivars were evaluated under eight graded NaCl treatments to determine species-specific salt tolerance thresholds. Representative cultivars were further analyzed for physiological, biochemical, and transcriptomic responses under medium (0.4-0.6%) and severe (0.8-1.2%) salinity to elucidate adaptive strategies. Sunflower exhibited strong growth resilience and a biphasic sodium (Na⁺) allocation pattern, initially directing Na⁺ to shoots for osmotic adjustment under medium stress, followed by enhanced root sequestration under severe stress. This was accompanied by high antioxidant enzyme activities (SOD, POD), minimal oxidative damage, and root-specific upregulation of stress-responsive genes including UBP15 , SPNS , and KEG . In peanut, salt tolerance was associated with moderate germination tolerance, root-based Na⁺ compartmentalization, transient antioxidant and ROS-scavenging activity, and localized expression of calcium signaling ( CML19 , ACA13 ) and ion transport genes ( PAT8 , PLT4 ). Soybean displayed superior germination and flexible Na⁺ distribution pattern, retaining Na⁺ in roots under low salinity and facilitating shoot translocation under high salinity. This was coupled with elevated antioxidant activities and shoot-preferential expression of transcriptional regulators ( CRK7 , RAP2.2 , MYB84 , PYR1) . Additionally, soybean shoots exhibited dynamic transcriptomic reprogramming under varying salinity, with key regulatory genes ( CTR1 , KNAT7 , WRKY23 , MKP1 ) mediating Na⁺ exclusion under medium stress and redistribution under severe stress. Together, these results highlight integrated ion homeostasis, ROS detoxification, and transcriptional adjustments as core mechanisms underlying salt tolerance across diverse oilseed crops. • Root Na⁺ retention underlies salt tolerance in soybean and peanut. • Soybean shifts root Na⁺ to stems under severe salinity, while peanut retains it. • Sunflower restricts Na⁺ translocation from root to shoot under severe salinity. • Flavonoid and sugar pathways are activated in tolerant genotypes. • WGCNA reveals tissue-specific hub genes linked to tolerance and ion regulation.