Effects of 24-Epibrassinolide, melatonin and their combined effect on cadmium tolerance in Primula forbesii Franch

This study aimed to investigate the interaction between 24-Epibrassinolide (EBR) and melatonin (MT) and their effects on cadmium (Cd)-stressed Primula forbesii Franch. P. forbesii seedlings were hydroponically acclimatized at 6-7 weeks, then treated with Cd (200 Imol L-1), 24-EBR (0.1 Imol L-1), and MT (100 Imol L-1) after two weeks. Cd stress significantly reduced crown width, shoot, root length, shoot fresh weight, and fresh and dry root weights. Herein, 24-EBR, MT, and 24-EBR+MT treatments attenuated the growth inhibition caused by Cd stress and improved the morphology, growth indexes, and ornamental characteristics of P. forbesii under Cd stress. 24-EBR had the best effect by effectively alleviating Cd stress and promoting plant growth and development. 24-EBR significantly increased all growth parameters compared to Cd treatment. In addition, 24-EBR significantly improved the gas exchange parameters, activities of antioxidant enzymes, and the cycle efficiency of AsA-GSH. Furthermore, 24-EBR increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), dehy-droascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR) by 127.29%, 61.31%, 61.22%, and 51.04%, respectively, compared with the Cd treatment. Therefore, 24-EBR removed the reactive oxygen species produced by stress, thus protecting plants against stress damage. These results indicate that 24-EBR can effectively enhance the tolerance of P. forbesii to Cd stress.