Abstract: Expression patterns of the genes（KCS,KCR,HCD and ECR gene） involved in biosynthesis and accumulation of nervonic acid were studied and compared in high and low nervonic acid-yielding Xanthoceras sorbifolium Bunge during embryonic development using semi-quantitative RT-PCR technology. This will play an important role for understanding molecular mechaisms of biosynthesis and accumulation of nervonic acid in X. sorbifolium. The results showed that the expression levels of four genes were highest in embryos of two lines at the 40 days after anthesis compared to that of other developmental stages,and then the expression levels decreased or was very low during the subsequent embryo development. The expression level of KCS gene was higher in HNA line than LNA line at 40 d,but its expression level was lower in HNA line compared to LNA line at 54,68 and 81 d. In contrast to the KCS gene,the expression level of HCD gene was lower in HNA line than LNA line at 40 daa,whereas its expression level was higher in HNA line compared to LNA line at 54,68 and 81 d. The expression level of KCR gene was relatively low in HNA compared with LNA. The expression level of ECR gene in HNA was higher compared with LNA at 40 and 81 d. These results indicated that the 40 d was a critical stage for the accumulation of nervonic acid in embryonic development. KCS and ECR genes mainly regulate the biosynthesis of nervonic acid in the early stage of embryonic development （at 40 d）. The HCD gene regulates the biosynthesis of nervonic acid in the medium and late stages of embryonic development.

Key words: Xanthoceras sorbifolium Bunge, embryo, nervonic acid, KCS gene, semi-quantitative RT-PCR, expression analysis