Abstract:

This study investigated the impact of cadmium (Cd) stress on soybean seed germination and early seedling growth, and examined the potential alleviating effect of exogenous salicylic acid (SA). The experiment utilized the soybean variety ‘Zhonghuang 13’ and employed both paper germination and hydroponic methods. Various aspects including the antioxidant system, photosynthetic characteristics, nutrient absorption and transport, and stress resistance gene expression were analyzed under the influence of Cd and exogenous SA. Results showed that 2.5 μmol L^-1 CdCl₂ stress led to oxidative damage in soybean embryos and seedlings, hindering nutrient absorption and transport as well as reducing photosynthesis, consequently inhibiting seed germination and early seedling growth. However, the addition of 50 μmol L^-1 SA mitigated the oxidative stress caused by Cd, resulting in reduced Cd accumulation, enhanced nutrient absorption, and improved photosynthesis. Specifically, under Cd stress, the application of SA decreased the levels of H₂O₂, O₂^-, and MDA in both leaves and roots, while also reducing Cd content in the leaves and increasing the contents of essential elements such as Ca, Cu, Fe, Mg, and Zn. Moreover, the net photosynthetic rate (P_n) and maximum photosynthetic efficiency of PSⅡ (F_v/F_m) were significantly improved with SA treatment compared to Cd stress alone. Exogenous SA up-regulated the expression of antioxidant system genes in soybean seedlings while down-regulating the expression of Cd transporter genes DMT, IRT, and MT1. This led to an increase in antioxidant enzyme activity, a reduction in Cd absorption by seedlings, promotion of nutrient absorption and transport, enhancement of photosynthesis, and alleviation of stress damage caused by Cd during soybean seed germination and early seedling growth.

Key words: soybean, salicylic acid, cadmium stress, seed germination, seedling growth, gene expression