Effects of exogenous 2, 4-epibrassinolide on growth and photosynthetic physiological characteristics of cucumber seedlings under cadmium stress

To explore the effects of exogenous plant hormones on plant growth and physiological characteristics under heavy metal stress, hydroponic test method was used to study the effects of 2, 4-epibrassinolide（EBL） on the growth and photosynthetic physiological characteristics of cucumber seedlings under cadmium stress. The results showed that 100 μmol · L^-1cadmium stress reduced the activities of antioxidant enzymes, and the activities of SOD and CAT in leaves were reduced by 28.80%and 19.57%, respectively, compared with the control, which aggravated the degree of membrane lipid peroxidation, destroyed the structure of thylakoid membrane of cucumber, inhibited photosynthesis, and reduced biomass to increase cadmium accumulation. Spraying 0.5 μmol · L^-1EBL on leaves could improve the activities of SOD, POD and CAT under cadmium stress. Compared with cadmium treatment,the activities of SOD and CAT in leaves were increased by 11.70% and 11.90%, respectively. The MDA content of cucumber was reduced, the integrity of leaf cells was maintained, the PSII reaction centers were protected, and the photosynthetic pigment content and net photosynthetic rate were increased to improve the photosynthetic performance, increase biomass, and reduce the cadmium accumulation in the aboveground and root of cucumber seedlings to promote the growth of cucumber seedlings under cadmium stress. In summary, EBL reduced Cd toxicity to cucumber seedlings by improving antioxidant capacity and leaf photosynthetic performance.