Abstract: In order to further explore Brassinosteroids (BRs) roles in response to chilling stress in plants, the suspension cultured cells of Chorispora bungeana were treated with or without 24-epibrassinolide (EBR) with successive culture for 5 days at 0 ℃. The results indicated that EBR treatment significantly increased the contents of proline, soluble protein and soluble sugar in the suspension cultures under low temperature conditions, suggesting that EBR could promote the chilling tolerance of the cells by inducing the large accumulation of osmotic adjustment substances. In addition, phenylalanine ammonia-lyase (PAL) activity of the suspension cells was induced with significant increase after EBR treatment under low temperature stress, indicating EBR might enhance the chilling tolerance of the cells through activating the phenylpropanoids metabolic defense system to decrease the chilling injury. Moreover, the CbCOR15 expression was enhanced with a higher level in EBR-treated cells at earlier time points of cold treatment, which prevented the cell membrane hexagonal HII phase caused by low temperature and played significant roles in the stabilization of cell membrane structure and improvement of chilling tolerance at molecular level.

Key words: brassinosteroids, Chorispora bungeana, low temperature stress, chilling tolerance