基部被子植物关键类群的管状分子研究

【作者】 张小玲；

【导师】 任毅；

【作者基本信息】 陕西师范大学 ， 植物学， 2008， 硕士

【摘要】 管状分子是维管植物次生木质部的主要组成成分,包括导管,管胞和木质部纤维三种类型。目前认为管胞是最为原始的管状分子类型,它在进化的过程中向着导管分子和纤维分化。导管的起源和进化程度是被子植物从湿润环境到季节性生境乔迁的关键,是与维管植物的进化密切联系的。所以,导管的形态结构在植物分类和系统发育研究中具有重要地位,其进化程度反映着植物类群的进化程度。基部被子植物一直以来被认为是被子植物起源和演化研究的关键,包含了较多的祖先的形态和结构特征,为众多植物学家所关注。近年来,基于DNA序列证据的分子系统发育分析表明,被子植物可分为基部被子植物,单子叶植物(monocots)和真双子叶植物。基部被子植物包括最基部的ANITA类群、金鱼藻目(Ceratophyllales)、金粟兰科(Chloranthaceae)、林仙目(Winterales)、胡椒目(Piperales)、樟目(Laurales)、木兰目(Magnoliales)。本次研究根据APG系统,选择基部被子植物中具有关键系统位置的13个科18个种为代表,利用扫描电子显微镜对其次生木质部管状分子的形态进行了详细的观察,以期通过对这些原始植物类群中管状分子的比较研究,揭示导管的起源以及早期进化过程中,端壁穿孔板,纹孔膜残余,侧壁纹孔等形态特征的演化。讨论导管进化与基部被子植物系统位置的相互关系等问题。根据我们的实验结果:Amborella(Amborellaceae)茎的次生木质部中管状分子明显具有向导管进化的趋势,是管胞向导管进化的过渡状态且已经形成了初步的导管雏形:Drimys wintera(Winteraceae)的管状分子形态较Amborella的更为原始,是管胞向导管过渡状态,没有形成导管:金粟兰科(Chloranthaceae)植物金粟兰属(Chlorantus),草珊瑚属(Sarcandra)植物茎的次生木质部中已经具有了原始的导管。通过这三个类群中管状分子形态的比较研究,显示了管胞向导管进化是一个连续的过程,管状分子端壁纹孔失去纹孔膜转变为穿孔,穿孔扩大,聚集形成穿孔板。端壁穿孔板与侧壁纹孔的显著差异是导管形成的主要特征。导管端壁的进化水平在基部被子植物类群中具有多样性,现存所有被子植物的姐妹群Amborella具有原始梯形端壁的导管雏形,lllicium的导管为端壁具有狭长的梯形穿孔板的原始类型,Austrobaileya,Monimiaceae导管端壁梯形横隔数目相对较少,Calycanthaceae,Lauraceae以及Piperaceae具有进化的单穿孔板的导管类型。显示了导管从原始梯形穿孔板到单穿孔板的进化过程。结合基部被子植物类群导管分子的形态,以及不同类群分支的年代我们能够粗略估计导管分子在各个类群的进化速率。在基部被子植物中,各个类群的共同祖先具有原始的管状分子形态,为管胞类型,这说明了基部被子植物各个大的类群中,导管是独立起源,各自独立进化的。不同的类群分支之后,其管状分子平行进化,进化速率各不相同。在Drimys,Amborella以及Chloranthaceae植物中,有部分管状分子端壁纹孔膜完全缺失,部分具有不同程度的纹孔膜残余。纹孔膜残余在这三个类群的出现说明了管胞向导管的过渡,并且纹孔膜残余的多少是判断其管状分子是否形成导管的重要依据。在Illicium,Schicandra,Eupomatia及Monimiaceae导管具有梯形穿孔板的类群中,大部分导管端壁纹孔膜完全缺失,而有的导管端壁具有不同程度的纹孔膜残余。纹孔膜的有无在这些类群中并不是判断导管形成的标准,而只是一个说明其导管原始性的特征,并且也说明了导管进化过程中各个性状的进化速率不是一致的。根据端壁穿孔板的进化水平以及植物类群的系统位置,我们认为导管侧壁纹孔的原始类型为小的圆形纹孔,散布或呈纵列排列侧壁上。随着导管的进化,直径的加粗,侧壁纹孔横向伸长形成梯形,或是数目增加,排列方式发生改变,形成成对列或互列纹孔。在梯形纹孔和对列纹孔之间有一系列的过渡类型。导管与射线细胞接触的侧壁纹孔较大,聚集,以更有利于水分的输导。在基部被子植物类群中,内壁纹饰的现象并不是很普遍,仅在Illicium henryi,Chimonanthuspraecox植物的导管内壁具有螺旋状加厚纹饰,Litsea tsinlingensis导管内壁有纹孔联合凹槽,这可能和它们处于温带季节性气候的生境有关。网状穿孔在基部被子植物中并不是很普遍,但是从Drimys winteri,Amborella trichopoda,Chloranthus multistachys,Chloranthus elatior及Illicium henryi植物导管具有的原始形态的网状穿孔及普遍的梯形横隔分义,交叉的现象,Eupomatia laurina,Schisandra sphenanthera典型的网状穿孔的出现,我们可以初步推断导管进化过程中,端壁多列排列的穿孔扩大形成网状穿孔,横向排列的网状穿孔间竖隔退化消失,网状穿孔横向融合形成梯形穿孔。更多还原

【Abstract】 Tracheary elements, including vessel elements, tracheids and fibres, are important members of secondary xylem in vascular plants. It is considered that tracheids are the most primitive tracheary elements, that evolved into vessel and fibre phylogenetically. The origin and evolution of vessel is a key factor for plants removing from wet areas to seasonal dry areas and is closely related to the evolution of vascular plants. So, the morphology characters of vessel elements bear important signification in plant taxonomic and phylogenetic researches and the vessel evolution reflects the evolution level of vascular plants.Basal angiosperms are considered as the key groups for the origin and evolution researches of angiosperms, have many ancestral morphology, therefore, attracted much attention of botanists. In recent years, molecular phylogenetic analysis based on multiple genes showed that angiosperms could be grouped into basal angiosperms, monocots and eudicots. Basal angiosperms contain ANITA group, Ceratophyllales, Chloranthaceae, Winterales, Piperales, Laurales, and Magnoliales. In this research we selected 18 species of 13 families in basal angiosperms as representatives for studying their tracheary elements with SEM. We wished to uncover the morphologic changes of perforation plates on end walls, pit membrane remnants and lateral wall pitting in the evolution of vessel elements, and to discuss the relationship of vessel evolution and phylogenetic progress of basal angiosperms. Here we show that:Tracheary elements in secondary xylem of Amborella (Amborellaceae) have the tendency of transformation from tracheids to vessel elements, and have already formed primitive vessel elements. Secondary xylem in Drimys wintera (Winteraceae) are even more primitive without really vessel elements present. Primitive vessel elements have presented in Chloranthus and Sarcandra of Chloranthaceae. Tracheary elements in these three groups show that transition from tracheids to vessel elements is a continuous progress. Vessel elements are formed by losting pit membranes in perforations on end walls, and congregating and enlarging of the perforations to form scalariform perforation plates on end walls of tracheary elements. The difference between perforation plates on end walls and lateral walls is the key feature for vessel elements origin.The evolution levels of vessel elements in basal angiosperms are various. There are incipient vessel elements with scalariform ends in Amborella; Vessel elements have long scalariform perforations plates with numerous bars in Illicium, have scalariform plates with less bars in Austrobaileya and Monimiaceae, and have formed simple perforation plates on end walls in Calycanthaceae, Lauraceae and Piperaceae. It shows the tendency of transformation from scalariform perforation plate to simple perforation plate. We could estimate the evolution rate of tracheary elements in various basal angiosperms based on different evolution levels of tracheary elements in different plants families and the origin times of these plants families. In basal angiosperms, the common ancestor of various groups bear primitive tracheary elements as tracheid type, so the vessel in different branches were not unitary origin and evolved independently. After origin of plant groups, their tracheary elements evolved parallelly with different evolutionary rate.Tracheary elements in Winteraceae, Amborellaceae and Chloranthaceae have various degree of pit membrane remnants in end walls. Present of pit membrane remnants in these three groups show the transition from tracheids to vessel elements is a continuous progress and presence or absence of pit membranes in end walls is used to differentiate the two cell types. Some of vessel elements in Illiciaceae, Schicandraceae, Eupomatiaceae and Monimiaceae have various degree of pit membrane present in scalariform perforations plates, which couldn’t account for transition from tracheids to vessel elements in these families, but show primitiveness of the vessel elements.According to the evolution level of vessel perforation plates and the phylogenetic position of plants groups, we can presume that the small circular pits scattering or arranging in single row on lateral walls of vessel elements could be primitive type. As the diameter of vessel elements increasing in evolution progress, pits on lateral walls enlarge transversely to form scalariform or increase in quantity, arrange in different patterns to form opposite or alternate. There are transitional types between scalariform, opposite and alternate lateral pitting. Pitting between vessels and rays are much larger than intervascular pitting, maybe it is for more effective in transverse water transport.Helical sculptures on vessel walls are not extensive in basal angiosperms, there are helical thickenings in Illicium henryi and Chimonanthus praecox, and grooves interconnecting pit apertures in Litsea tsinlingensis. Maybe this feature is related to ecological factors.Reticulate perforation plates are not extensive in basal angiosperms, there are several primitive reticulate perforations and forked or interconnected bars in scalariform perforation plates in Drimys winteri, Amborella trichopoda, Chloranthus multistachys, Chloranthus elatior and Illicium henryi, and typical reticulate perforations in Eupomatia laurina, Schisandra sphenanthera, showing that several rows of small circular perforations on end walls enlarged to form reticulate perforations, and the bars between paratactic reticulate perforations degenerated and clear away to form scalariform perforation.更多还原