Abstract:In order to investigate the effects of IAA on physiological response and cadmium tolerance of Trichosanthes kirilowii Maxim. under cadmium stress, Baoding T. kirilowii (cadmium-tolerant) and Pujiang T. kirilowii were selected as experimental materials, and soil culture experiments were conducted to determine the effects of exogenous IAA (10, 35 and 60 μmol/L) on physiological changes, photosynthetic characteristics, antioxidant enzyme activity and malondialdehyde (MDA) content of these two varieties under 800 μmol/L cadmium stress. The results showed that:(1) Compared with the CK, the average root length, fresh weight of underground part, superoxide dismutase (SOD) activity, chlorophyll content, maximum photochemical efficiency (Fv/Fm) and electron transfer rate (ETR) of the two kinds of T. kirilowii significantly decreased under 800 μmol/L Cd treatment, while the initial fluorescence (Fo), peroxidase (POD) activity, catalase (CAT) activity and MDA content increased significantly, and the lipid peroxidation of cell membrane deepened. (2) With the increasing of IAA concentration, the average root length and fresh weight of underground part of Baoding T. kirilowii increased continuously, with the maximum increase of 24.83% and 40.55%, while those of Pujiang T. kirilowii changed from ascending to descending. (3) After the addition of IAA, the content of chlorophyll a, b, a+b and chlorophyll a/b, Fv/Fm, ETR, SOD, POD and CAT activities in the young leaves of the two varieties increased first and then decreased, while Fo and MDA content dropped firstly and then increased. The content of chlorophyll a, b, a+b, a/b, Fv/Fm, ETR, SOD and CAT increased to the peak values with the addition of IAA at 35 μmol/L, while MDA decreased by 35.44%~43.23%, reaching the valley value. (4) The analysis of membership function indicated that the ability of cadmium tolerance of different IAA concentrations was 35 μmol/L > 10 μmol/L > 60 μmol/L > 0 μmol/L. Therefore, applying exogenous IAA has a certain application prospect in alleviating cadmium stress in plants.