Abstract: Aiming to study the tolerance mechanism of Paulownia fortunei to heavy metal cadmium, Paulownia tomentosa×P.fortunei 33 was used as experimental material to study the absorption and accumulation characteristics, root morphology, physiological characteristics and subcellular distribution characteristics of Cd under different concentrations of cadmium stress. The results showed that under different concentrations of cadmium stress, the Cd content in all parts of Paulownia tomentosa×P.fortunei 33 showed root > leaf > stem; With the increase of cadmium stress concentration, root length, root volume and root surface area, non protein sulfhydryl（NPT） content of seedlings increased first and then decreased, glutathione（GSH） content decreased significantly, chelating peptide（PCS） content increased significantly, the proportion of Cd content in cell wall and cell fluid increased, MDA content in roots and leaves increased significantly, and SOD activity in leaves did not change significantly, SOD activity in roots decreased first and then increased. When the cadmium concentration was higher than 20 mg/L, the POD activity of plants and CAT activity of roots increased significantly, the cat activity of leaves increased first and then decreased, and the proline content of roots and leaves increased significantly. In conclusion, Paulownia tomentosa×P.fortunei 33 can improve the tolerance and enrichment of cadmium by enhancing the activities of SOD, pod and cat in roots, pod and cat in leaves and accumulating osmotic regulators; The retention of Cd by root cell wall, the compartmentalization of Cd by cell fluid in stem and leaf and the chelation of Cd by non protein sulfhydryl compounds may be the main reasons for Paulownia tomentosa×P.fortunei 33 to tolerate Cd stress.

Key words: cadmium（Cd）, Paulownia tomentosa×P.fortunei33, root morphology, antioxidant enzyme, non-protein sulfhydryl, subcellular distribution