Initial Physiological and Molecular Adjustments Underpin Salinity Tolerance During Wheat Germination and Early Seedling Development

Global warming and associated environmental changes are reducing arable land and intensifying salinization risks, posing growing threats to food security. Soil salinity is an increasing threat to agricultural productivity worldwide, particularly in arid and semi-arid areas. Wheat (Triticum aestivum L.) is one of the most important and widely cultivated cereal crops for human consumption and livestock feed. However, with increasing water scarcity and the incidence of salt-affected lands, wheat productivity is increasingly affected by salinity. Previous studies have investigated salinity tolerance mechanisms mainly at the seedling and reproductive stages of wheat; however, comparatively fewer studies integrate rapid biochemical and physiological responses during the first hours of germination stress exposure together with transcriptional analyses during early seedling establishment, even though this stage is critical for stand establishment. Here, we evaluated early physiological and transcriptional responses of salt-tolerant, moderate, and sensitive wheat cultivars exposed to 0 or 150 mM NaCl during germination and the early seedling stage. Tolerant and sensitive cultivars showed contrasting germination performance under salinity. Physiological analysis showed that salt-tolerant cultivars exhibited higher proline accumulation and higher antioxidant enzyme activities (CAT, SOD, and GR), while maintaining lower MDA levels under salinity compared with sensitive cultivars. Notably, tolerant cultivars showed marked upregulation of TaHKT1;4, TaP5CS, TaMYB, and TaDHN genes associated with ion homeostasis, osmoprotectant metabolism, and stress-responsive regulation. These responses represent integrated early-stage biochemical, physiological, and transcriptional indicators of salinity responsiveness rather than direct predictors of final yield performance.