Abstract:Cytochrome P450 monooxygenase (CYP450) is the largest enzyme family involved in plant metabolism, among which CYP734A subfamily members are widely involved in the inactivation of plant hormone Brassinosteroids (BRs). In order to analyze the effects of BRs on Hordeum vulgare L. var. nudum Hook. f.(highland barley), which is a characteristic plant in QinghaiTibet plateau, we treated the seedlings of highland barley cultivar ‘Dulihuang’ with the synthetic hormone 24epibrassinolide (24eBL) or BRs synthetic inhibitor brassinazole (BRZ). In order to deeply analyze the function of HvBAS1, we cloned the cDNAs from highland barley by RTPCR, and detected their expression characteristics by realtime quantitative PCR. The results showed that: (1) 24eBL could significantly promote the growth of highland barley seedlings, while BRZ was opposite. (2) Two subfamily members of CYP734As were cloned from highland barley. Due to their high homology with Arabidopsis BAS1, they were named HvBAS11 and HvBAS12. HvBAS11 was 1 629bp in length and encoded 542 aa, while HvBAS12 was 1 689 bp in length and encoded 562 aa. The homology of amino acid sequences between them was 76.42%. The results of subcellular localization predicted that both of them existed in endoplasmic reticulum. (3) Realtime quantitative PCR detection showed that the expression patterns of HvBAS11 and HvBAS12 were completely different, in which the expression of HvBAS11 in the roots was higher than that in the leaves, while the expression of HvBAS12 in the leaves was higher than that in the roots. With the increase of seedling age, the expression of HvBAS11 in the roots showed a trend of first increasing and then decreasing, but HvBAS12 decreased firstly and then increased in leaves. After BRZ treatment, both HvBAS11 and HvBAS12 were significantly downregulated compared with the control, and the expression level of HvBAS12 were decreased even more. The results indicated that both HvBAS11 and HvBAS12 were probably involved in inactivation of endogenous BRs in highland barley, but their functions were different.