Exogenous salicylic acid reduces cadmium content in spinach (Spinacia oleracea L.) shoots under cadmium stress

Consumption of leafy vegetables is a primary route of cadmium (Cd) exposure in the human body. Salicylic acid (SA) is a major stress signaling molecule that alleviates Cd toxicity in various plants. Our study aimed to investigate the effects of different SA concentrations on spinach growth, cadmium accumulation, and stress resistance physiology under cadmium stress (50 µmol/L). Cd stress significantly markedly decreased spinach growth and biomass, reduced its photosynthetic efficiency, increased activities of antioxidative enzymes, and upregulated the relative expression of several genes involved in cadmium absorption and transport compared to the control. The exogenous application of SA mitigated the harmful effects of Cd in spinach. 0.8 and 1.6 mmol/L SA significantly increased spinach root length, plant height, and biomass and decreased the Cd content in shoots by 30.03 and 17.35% compared to the Cd-treated group. Moreover, SA alleviated the yellowing of leaves caused by Cd stress. Exogenous SA ameliorated Cd toxicity in spinach by reducing reactive oxygen species, malondialdehyde, proline, and soluble protein levels. Exogenous SA application reduced Cd absorption in spinach leaves by downregulating the expression of genes involved in Cd transport, such as SoHMA4-like, SoNramp3.1-like, SoNramp6-like, and SoNramp7.2-like. Principal component analysis and correlation analysis showed that exogenous SA application under Cd stress was correlated with plant Cd content, photosynthetic pigment content, and relative expression of Cd absorption and transportation-related genes. To summarize, these findings indicate that SA mitigates Cd toxicity in spinach by reversing the adverse effects of Cd stress on plant growth and reducing Cd accumulation in the shoots.