Indole Butyric Acid Alleviated Cadmium Toxicity in Lettuce by Increasing the Polysaccharide Contents and the Cadmium-Binding Capacity of Root Cell Walls

The purpose of this study is to explore the physiological mechanisms underlying the attenuation of cadmium (Cd) toxicity using indole butyric acid (IBA) in lettuce. In this study, hydroponic experiments were conducted and 0.5 µM IBA was applied to hydroponic solution with 20 µM Cd. The photosynthetic parameter, polysaccharide contents and Cd contents of root cell walls, accumulation of reactive oxygen species (ROS) and antioxidant enzyme activities, mineral elements in lettuce were detected. Exogenous IBA greatly reduces the toxic symptoms caused by Cd in lettuce seedlings. IBA improved the retention of Cd in the roots under cadmium stress, with the majority of Cd being fixed in the cell wall’s hemicellulose 1 and pectin. Furthermore, IBA increases nutrient (Ca, Mg, Fe, Mn) assimilation or transportation in lettuce to variable degrees, which contributes to enhanced photosynthesis during cadmium stress. Additionally, IBA increased Catalase (CAT) and Peroxidase (POD) activity and reduced the accumulation of ROS in lettuce leaves, protecting the photosynthetic system. Taken together, these results demonstrate that IBA can improves photosynthesis and growth by increasing Cd fixation in the root, photosynthesis related elements absorption, and ROS-scavenging capacity in lettuce. IBA application is a promising method to alleviate Cd toxicity in lettuce and could be explored in phytoremediation.