Effects of amino acids on the germination and Cd accumulation in soybeans exposed to cadmium.

Cadmium (Cd) has emerged as a major pollutant in agricultural soils and is known for its strong bioaccumulation potential and high toxicity even at low concentrations. Soybeans, an important grain crop in China, are particularly vulnerable to Cd contamination, which adversely affects germination and yields. Amino acids mitigate Cd toxicity and may influence Cd uptake in plants. This study aimed to evaluate the capacity of selected amino acids to mitigate Cd-induced toxicity during soybean seed germination and to investigate their effects on Cd uptake and accumulation in seedling tissues. Soybean seeds were exposed to varying Cd concentrations (0-500 mg/L), with or without amino acid supplementation. At low Cd concentrations (0-50 mg/L), the germination rate showed a slight decline, followed by recovery. However, at 100 mg/L, germination significantly decreased, and at 500 mg/L, it decreased to 2.5%. The application of histidine, serine, tyrosine, cysteine, and methionine to seeds exposed to 500 mg/L Cd significantly increased germination compared to untreated Cd-exposed seeds, with improvements ranging from approximately 2- to fivefold, and the highest recovery was observed in cysteine-treated seeds (up to 13.2%). Notably, the Cd content per gram of tissue was higher in amino acid-treated seedlings than in untreated controls, suggesting that amino acids may chelate Cd ions and facilitate their uptake, thereby alleviating toxicity during germination and promoting increased Cd accumulation in tissues. In conclusion, although specific amino acids can partially restore germination under high Cd stress, they may also enhance Cd accumulation in soybean seedlings.