Seed priming-mediated molecular responses enhance thermo-osmotic resilience in Halophila ovalis for climate-resilient restoration.

Marine heatwaves pose significant threats to seagrass ecosystems, particularly during early life stages where recruitment governs population stability. In this study, we investigated propagule quality and stress tolerance mechanisms in the tropical seagrass Halophila ovalis by integrating density-based seed selection, antimicrobial storage, thermal priming and gene expression analysis. Density-gradient fractionation revealed clear stratification of seed quality, with high-specific-gravity seeds (SG > 1.20) exhibiting 78% germination compared to <12% in low-density fractions, indicating strong variation in physiological integrity. Storage experiments demonstrated that silver nanoparticle treatment (2 ppm AgNP) effectively preserved seed viability for up to 6 months, whereas copper treatments showed comparatively lower efficiency. Seedlings derived from high-density seeds were subjected to thermal priming (36 °C/40 psu) prior to exposure to extreme stress (41 °C/42 psu). Progressive 5-day priming significantly enhanced stress tolerance, with seedlings maintaining high survival (∼93%), shoot growth and photosynthetic area comparable to controls, while non-primed seedlings exhibited ∼31% mortality and ∼30% tissue loss. Biochemical responses indicated ∼60% lower lipid peroxidation (MDA) in primed seedlings, accompanied by elevated antioxidant capacity. At the molecular level, priming induced strong upregulation of stress-responsive genes, including HSPA1 (∼22-fold), SOD3 (∼21-fold) and osmoregulatory genes (VP1, SOS1) under stress conditions. Notably, this study provides the first integrative evidence linking seed quality optimization, antimicrobial storage and priming-induced molecular responses to enhanced thermo-osmotic stress tolerance in H. ovalis. These findings demonstrate that coordinated physiological and molecular acclimation strategies can significantly improve stress resilience in seagrass systems, supporting their application in climate-resilient restoration as nature-based solutions.