Physiology and proteomics reveal Fulvic acid mitigates Cadmium adverse effects on growth and photosynthetic properties of lettuce

Understanding the molecular mechanisms of plants in response to Cd stress is crucial for improving plants adaptation to Cd stress. Fulvic acid (FA) is an active humic substance that is often used as a soil conditioner. However, there are few reports on the role of FA against Cd stress. The aim of this study was to determine the effects of Fulvic acid on alleviation of Cd toxicity in lettuce (Lactuca sativa L) under hydroponic conditions. Our results showed that 20 mu mol/L Cd stress significantly reduced photosynthetic pigment metabolism and the expression of photosynthetic apparatus-related proteins, thereby inhibiting photosynthetic electron transport, net photosynthetic rate and negatively affecting photosynthetic carbon assimilation and growth of lettuce. However, proteomic findings suggest that the application of FA can reduce the adverse effects of Cd contami-nation. Compared to Cd stress alone, FA significantly increased the expression of Light-harvesting proteins, re-action center and electron transport-related proteins. Further results showed that FA at 0.5 g/L reduced the uptake of Cd by the roots, resulting in a 23.5% reduction in total Cd content in lettuce. Moreover, FA enhanced S metabolism and rebuilt redox homeostasis in cells. Overall, these findings provide new insights into the mech-anism of cadmium toxicity mitigation in lettuce by FA. Which is recommended as an eco-friendly tool for improving the photosynthesis performance and biomass of lettuce under Cd stress.