苏铁在种子植物进化中的位置——分子生物学的证据

Molecular Evidence for the Status of the Cycad Cycas revoluta in Seed-plant Evolution

用大分子rRNA快速测序法测定了苏铁(Cycas revoluta Thunb.)、水松[Glyptos-trobus pensilis(Staunt.)Koch]和南方红豆杉[Taxus mairei(Lemee et Levl)S.Y.Hu]三种裸子植物Ls-rRNA5′端区108个核苷酸的序列。用这些数据构建的rRNA系统树揭示了苏铁与水松和南方红豆杉构成一个关系密切的姐妹群,而所分析的被子植物都为另一自然类群。另以绿藻作为种子植物群外参照物种,表明苏铁这一位置并不是由于一个特异的进化速度所造成的。这一结果支持了苏铁与松杉类为一自然群类,它们的分歧发生在裸子植物与被子植物分歧之后的假说。

More than 100 nucleotides of the 5'terminal region of Ls-rRNA from Cycas revo-luta Thunb,, Glyptostrobus pensilis (Staunt.) Koch and Taxus mairei (Lemee etLevl) S.Y. Hu were determined by the rapid rRNA sequencing method. The phy-logenetic tree of rRNA constructed with these data reveal that the Cycad and coni-ferous trees constitute a closely related sister group, whereas the angiospermsform another monophyletic group. This position of the Cycad is not the result ofan aberrant rate in molecular evolution, indicated by Pyramimonas parkeae as anoutgroup reference. Our result support the hypothesis that the Cycad and conife-rous trees were a monophylatic group and the seperation of these species occuredafter their seperation from the ancestor of flowering plants.