CaCl2 Priming Boosts Salinity-Alkalinity Tolerance in Germinating Soybean by Reducing DNA Oxidative Damage and Enhancing Ca2+ -ROS Signaling Crosstalk.

Soybean (Glycine max) seed germination is highly sensitive to saline-alkaline stress. Seed priming represents an effective strategy to mitigate its detrimental effects. However, the optimal priming conditions (agent, concentration, duration) and the underlying molecular mechanisms remain poorly understood. This study investigated the effects of priming with distilled water (Control), calcium chloride (CaCl2), melatonin (MT), and proline (Pro) under saline-alkaline stress on soybean seed germination and the molecular basis of enhanced tolerance. Evaluation of ten germination-related parameters revealed that priming with 100 mM CaCl2 for 12 h significantly enhanced the germination rate. Physiological analyses demonstrated that CaCl2 priming effectively reduced reactive oxygen species (ROS) accumulation by increasing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), while decreasing malondialdehyde (MDA) content. Furthermore, CaCl2 priming activated the Ca2+ signaling pathway by increasing radicle Ca2+ content and upregulating the expression levels of Ca2+ signaling-related genes (e.g., GmCAM7, GmCNGC2, GmCNGC19, GmMPK2, and GmMKK2). Additionally, CaCl2 priming significantly enhanced DNA damage repair capacity of soybean cultivars with differing saline-alkaline tolerance. This was manifested by reduced DNA oxidative damage and decreased random amplified polymorphic DNA (RAPD) polymorphism, thereby enhancing genomic stability and alleviating cell cycle arrest. These findings deepen our understanding of the complex regulatory role of calcium signaling in plant abiotic stress responses and provide important novel theoretical insights for improving crop resilience.