Abstract：To study the effects of Bacillus thuringiensis on rice (Oryza sativa) seedling under cadmium stress, the plant growth parameters of germination rates of rice seeds, the yellow and brown rates of rice seedlings and chlorophyll content were determined by direct measurement method, apparent observation and ultraviolet spectrophotometry. Atomic force microscopy was applied to observe the surface changes of B. thuringiensis before and after cadmium treatment, and some granular dots were found on the bacterial surface, which implied there was surface adsorption of cadmium on B. thuringiensis, indicated that B. thuringiensis could be a potential bacterium in the practical applications of Cd2+ contaminated bioremediation on rice soil. Additionally, the growth of rice seedling was significantly inhibited under the cadmium stress, and the inhibition activity was enhanced with the increasing concentration of cadmium. However, the seedlings had no significant difference of shoot height and root length in 50 and 400 mg/L Cd2+ treatment groups between Cd and Cd+Bt groups (P＞0.05), which indicated that there was no significant changes in the shoot height and root length of the seedlings before and after Bt treatment under the cadmium stress. The significant difference of chlorophyll a and b was found in 100 and 400 mg/L Cd2+ treatment between Cd and Cd+Bt groups (P＜0.05). The rice seed germination rate had significant difference in 200 mg/L Cd2+ treatment group between Cd and Cd+Bt groups (P＜0.05). Meanwhile, the yellow rate and brown spot rate of Cd+Bt and Cd treatments were also monitored. It was found that the yellow rates had significant difference in 50 and 400 mg/L Cd2+ treatment between Cd and Cd+Bt groups (P＜0.05). In addition, the brown spot did not appear in the treatment group of 50 mg/L Cd2+, while the brown spot rate had significant difference in 400 mg/L Cd2+ treatment between Cd and Cd+Bt groups (P＜0.05), which indicated that both the yellow rate and brown spot rate of Cd+Bt were lower than the Cd treatment. The above results demonstrated that B. thuringiensis could reduce the concentration of free cadmium in rice soil by adsorption process, thereby relieve the cadmium stress and increase the chlorophyll content of rice seedlings. The present work provides a theoretical basis for the application of the Bt strain in the field of cadmium contamination.
