用rDNA的ITS序列探讨绵刺属的系统位置

A REEVALUATION OF THE STATUS OF POTANINIA BASED ON INTERNAL TRANSCRIBED SPACER SEQUENCES

绵刺属由于其特殊的形态特征 ,其系统位置至今仍存在争议。本文选定了蔷薇亚科 6种植物和李亚科 1种植物 ,扩增并测定了其核糖体DNA的ITS序列 (不包括 5 .8S片断 )。分析时又从GenBank中选取了蔷薇科另外 5种植物的ITS序列共同分析。比较这 1 2种植物的ITS1 +ITS2 ,发现不同植物间序列长度变异较大。ITS1的长度范围为 2 2 4～ 2 66bp ,ITS2的长度范围为 2 0 2～ 2 2 1bp。用PAUP 3.1 .1软件对 1 2种植物的ITS1 +ITS2进行分析 ,结果表明蔷薇亚科中和绵刺属亲缘关系最近的属为金露梅属 ,其次为地蔷薇属 ,再次为山莓草属 ,而这4个属均具有花柱基侧生的特点 ,这与传统上依据花托杯状或坛状将绵刺属放在蔷薇属和龙牙草属附近的处理不符。系统树上李亚科的 2种植物明显地聚为一个单系类群 ,说明绵刺与蒙古扁桃关系相对甚远。研究结果还表明绵刺这一蒙古高原旱生植物区系成分是由东亚中生植物区系成分的银露梅演化而来 ;绵刺的各种形态特征和生态习性是长期适应荒漠干旱气候环境的结果。这一植物起源及其迁移路线的发现 ,为深入研究亚洲中部荒漠植物区系和植被的形成提供了新的证据。

Because of its special feature of morphology, the phylogenetic status of Potaninia is still argued today.The ITS sequences of six species of Rosoideae and a species of Prunoideae are obtained in the study. The other five ITS sequences of five species of Rosaceae are gotten from Genbank and analyzed together. The result of comparing ITS1+ITS2 sequences of 12 plants shows that the sizes of sequences of different plants are different greatly. The sequences of ITS1 range from 224～266 bp. The sequences of ITS2 range from 202～221 bp. The result of phylogenetic analysis with PAUP 3.1.1 shows that Dasiphora is the closest genus with Potaninia;the second is Chamaerhodos;the third is Sibbaldia. The mutual feature of the three genera is that style grows from the end or side of ovary. Traditionally, Potaninia is arranged near Rosa and Agrimonia judged by torus like chalis or jar, which is not consistent with our result. The phylogenetic tree indicates that Prunus mongolica and Prunus cerasifera form a monophiletic taxa obviously, which show the relationship of Potaninia mongolica and Prunus mongolica is very far. The study also indicate Potaninia mongolica, a axerophilous floristic element of Mongolian Plateau, is derived from D.glabra, a mesophytic floristic element of East Asia;All morphological characteristics and ecological habit are the result adapting itself to dry climate of desert for ages. The discovery of derivation and migrating route provide the new proof for studying the formation of desert flora and vegetation of midst of Asia .