用核糖体DNA的ITS序列探讨中国柽柳科植物系统分类中的几个问题

Systematic studies on some questions of tamaricaceaebased on ITS sequence

采用 PCR直接测序的方法对中国柽柳科 3属 1 0种代表植物的 ITS序列进行了比较研究 ,结果表明 ,属内片段长度、GC含量和位点变异量上均比较一致 ;ITS- 1长度为 2 4 9～2 69,ITS- 2长度为 2 2 4～ 2 53,GC含量 46%～ 63% ,信息位点占总位点的 30 %。运用 PAUP软件分析得到单个最简约树 ,总步长为 395步 ,一致性指数 CI=0 .91 6,保持性指数 RI=0 .886。柽柳属的 6个类群具 1 0 0 %的强支持率聚为一类 ,其中 ,Tamarix elongata和 T.gracilis,T.karelinii和 T.hispida两两结合在一起 ,并分别得到 56%和 83%的 bootstrap支持。前者先和 T.arceuthoides结合 ,而后再与 T.karelinii- T.hispida分支结合。柽柳属 6个类群间的系统学关系与形态学及孢粉学证据相吻合。水柏枝属的 Myricaria laxiflora与 Myricariabracteata也具强的支持率 ( 1 0 0 % )而聚在一起。两大分支之间通过秀丽水柏枝 Myricariaelegans联系。秀丽水柏枝是源于柽柳属与水柏枝属两属的杂交后代 ,但遗传了更多柽柳属的特性。此外 ,探讨了 ITS序列在柽柳科系统学研究中的广阔应用前景。

The internal transcribed spacer (ITS) and partial 5.8 S rRNA gene (3end) of nuclear ribosomal DNA was sequenced for 10 representative species of three genera in the Tamaricaceae.The result indicates that there exist high sequence alignability and length conservation among ITS sequences within and between the genera.The sequence of ITS 1 in Tamaricaceae range in size from 249 to 269 bp and from 224 to 253 bp in ITS 2.Among 608 aligned sites of ITS and partial 5.8S rDNA sequences,199 are variable sites,among which,156 are informative.PAUP analysis was conducted using Reaumuria songarica as an outgroup and only one most parisimorous fitch tree was generated.Of which,the boot length is 495,CI=0.916 and RI=0.8866 species of Tamarix belong to a strougly supported clade with a bootstrap value of 100%;Another clade comprising two Myricaria species, M.laxiflora and M.bracteata ,was also well supported by the bootstrap analysis. M.elegans is situated at a transtitional position from Tamarix to Myricaria ,and closer to Tamarix .ITS sequence analysis is generally congruent with morphological and palynological evidence. M.elegans is a hybrid between Tamarix and Myricaria ,and has retained more characters of Tamarix .We also discussed the evaluation of ITS on the systematics research of Tamaricaceae,and predict that there will be a wildly use.