Ionic Homeostasis, Carbohydrate Metabolism, and Oxidative Balance Underlie Wild Soybean Resistance to Low Potassium Stress

The scarcity of potassium resources in farmland soils poses a major challenge to global food security. Wild soybean (Glycine soja), a valuable wild germplasm related to cultivated soybeans, is known for its high-stress resistance and adaptability. This study comprehensively compares two wild soybean ecotypes in terms of growth parameters, photosynthetic physiology, mineral ions and metabolite contents, and gene expression, aiming to clarify the regulatory mechanisms of low potassium stress tolerance in wild soybean seedlings' leaves. Results show that in barren-tolerant wild soybean (GS2), genes involved in potassium ion transport were significantly upregulated. This promotes potassium absorption and transport, maintaining a high K⁺ concentration and K⁺/Na⁺ ratio. Carbohydrate synthesis is enhanced in GS2, with increased sucrose and raffinose accumulation and a more active tricarboxylic acid (TCA) cycle. GS2 also strengthens the ascorbic acid-glutathione (ASA-GSH) cycle, along with promoting salicylic acid and 4-aminobutyric acid GABA synthesis, which boosts antioxidant capacity and reactive oxygen species (ROS) scavenging, maintaining oxidative balance. Under low potassium stress, GS2 accumulates unsaturated fatty acids, enhancing cell-membrane fluidity and providing a stress-resistant structural barrier. Overall, this study provides a basis for developing high-quality wild soybean resources and exploring genes for low potassium stress tolerance, which could contribute to improving cultivated soybeans' adaptability to potassium-deficient soils and ensuring global food production stability.