Molecular Cloning and Bacterial Expression of Germacrene A Synthase cDNA from Crepidiastrum sonchifolium

Germacrene A synthase（GAS） catalyzes the biosynthesis of germacrene A, which is a key precursor for sesquiterpone lactones. Cloning of a novel full-length cDNA encoding GAS from the medicinal plant Crepidiastrum sonchifolium（dosignated CsGAS） is reported in this study. The cDNA is 1837 bp long and contains a 1680-bp open reading frame encoding a 559 amino-acid protein. The functional expression of the cDNA in Escherichia coli, as an N-terminal thioredoxin fusion protein, with the pET32a vector yielding a recombinant enzyme. Sequence analysis was used to compare this enzyme with the mechanistically related epi-aristolochene synthase from tobacco, and the effect of possible involvement of a number of amino acids in sesquiterpone synthase on product specificity was also discussed.

黄瓜假还阳参不同部位黄酮提取及抗氧化活性

以黄瓜假还阳参为试材,采用60%的乙醇超声提取黄瓜假还阳参的根、老茎、嫩茎、叶、花蕾、花、种子中的总黄酮,用分光光度法测定各部位的总黄酮含量以及对DPPH自由基、羟基自由基的清除能力和还原力等抗氧化活性指标,通过测定不同部位的总黄酮含量及比较其抗氧化活性,以期为开发利用黄瓜假还阳参药用资源提供参考依据。结果表明:黄瓜假还阳参各部位的总黄酮(以芦丁计)含量由高到低依次为种子3.75 mg·g^(-1)、叶2.14 mg·g^(-1)、花蕾0.93 mg·g^(-1)、花(盛开期)0.69 mg·g^(-1)、嫩茎0.44 mg·g^(-1)、根0.34 mg·g^(-1)、老茎0.17 mg·g^(-1)。各部位提取物的DPPH自由基、羟基自由基清除能力和Fe还原力也存在差异,且抗氧化活性与提取物中总黄酮含量存在量效关系,种子中的总黄酮抗氧化活性最强。其开发利用以提取黄酮为目的时,黄瓜假还阳参适宜于种子成熟期采收;因叶片产量远高于种子,其黄酮含量也仅次于种子,也可选择叶片生长旺盛时期采收。