金沙江河谷苏铁天然植物群落的研究

近年在金沙江干热河谷及其邻近地区陆续发现的苏铁天然植物群落,为本属植物在欧亚大陆内陆分布的最北边缘。其中,面积最大和保存较好的是渡口市攀枝花苏铁(Cycas panzhihuaensis)植物群落。本文研究了这个群落的分布与生境、生长状况、外貌、种类组成以及群落的综合特征等。认为具有稀树草原的特点,而这里的稀树草原是次生性质的,苏铁群落是其中幸存的残遗植被类型。这对研究我国植物地理有着重要意义。     

贵州苏铁的核型分析

本文报道了贵州苏铁(Cycas guizhouensis)的染色体数目及核型,并与攀枝花苏铁(C.panzhihuaensis)、苏铁(C.revoluta)、华南苏铁(C.rumphii),拳叶苏铁(C.circinalis)和C.media等的核型进行了比较,讨论了苏铁属植物不同核型的进化趋势,提出了苏铁属植物的两种地理分布核型,即1.北回归线以北为K(2n)=22=2m+4sm+4st+12T包括贵州苏铁和攀枝花苏铁;2.北回归线及其以南为K(2n)=22=4m+8st+10T,包括苏铁、华南苏铁、拳叶苏铁和C.media。     

多歧苏铁的修订

中国特有种。产云南东南部元江流域,个旧、蒙自、屏边与河口交界处,海拔200-1000     

中国苏铁属花粉形态研究

对中国苏铁属花粉进行了光镜和扫描电镜观察。花粉中等大,极轴长２６．５－３５．７μｍ,赤道轴长２０．６－２６．４μｍ;极面观椭圆形至近圆形,赤道面观船形或肾形,具远极单沟,达两端,其开闭和形状随花粉干燥或潮湿而变化,内部具多种不规则突起,两端具皱纹;远极面外壁光滑或稀具微突起,近极面具穿孔,孔穴或蜂窝状纹饰。     

苏铁Cycas revoluta珊瑚根内生真菌的多样性

苏铁类植物是目前发现的唯一一类具有珊瑚根结构的裸子植物,是探究植物-微生物互作的理想材料。本研究通过高通量测序技术对中国13个地区栽培苏铁Cycas revoluta珊瑚根中的内生真菌组成及多样性进行分析,结果表明苏铁内生真菌多样性较高,但各地区间内生真菌的组成及多样性差异不显著,显示苏铁和珊瑚根内生真菌的共生与栽培地无关。     

Organelle DNA phylogeography of Cycas taitungensis, a relict species in Taiwan

The phylogegraphic pattern of Cycas taitungensis, an endemic species with two remaining populations in Taiwan, was investigated based on genetic variability and phylogeny of the atpB-rbcL noncoding spacer of chloroplast DNA (cpDNA) and the ribosomal DNA (rDNA) internal transcribed spacer (ITS) of mitochondrial DNA (mtDNA). High levels of genetic variation at both organelle loci, due to frequent intramolecular recombination, and low levels of genetic differentiation were detected in the relict gymnosperm. The apportionment of genetic variation within and between populations agreed with a migrant-pool model, which describes a migratory pattern with colonists recruited from a random sample of earlier existing populations. Phylogenies obtained from cpDNA and mtDNA were discordant according to neighbour-joining analyses. In total four chlorotypes (clades I-IV) and five mitotypes (clades A-E) were identified based on minimum spanning networks of each locus. Significant linkage disequilibrium in mitotype-chlorotype associations excluded the possibility of the recurrent homoplasious mutations as the major force causing phylogenetic inconsistency. The most abundant chlorotype I was associated with all mitotypes and the most abundant mitotype C with all chlorotypes; no combinations of rare mitotypes with rare chlorotypes were found. According to nested clade analyses, such nonrandom associations may be ascribed to relative ages among alleles associated with the geological history through which cycads evolved. Nested in networks as interior nodes coupled with wide geographical distribution, the most dominant cytotypes of CI and EI may represent ancestral haplotypes of C. taitungensis with a possible long existence prior to the Pleistocene glacial maximum. In contrast, rare chlorotypes and mitotypes with restricted and patchy distribution may have relatively recent origins. Newly evolved genetic elements of mtDNA, with a low frequency, were likely to be associated with the dominant chlorotype, and vice versa, resulting in the nonrandom mitotype-chlorotype associations. Paraphyly of CI and EI cytotypes, leading to the low level of genetic differentiation between cycad populations, indicated a short period for isolation, which allowed low possibilities of the attainment of coalescence at polymorphic ancestral alleles.     

Chloroplast genome (cpDNA) of Cycas taitungensis and 56 cp protein-coding genes of Gnetum parvifolium: insights into cpDNA evolution and phylogeny of extant seed plants

Phylogenetic relationships among the 5 groups of extant seed plants are presently unsettled. To reexamine this long-standing debate, we determine the complete chloroplast genome (cpDNA) of Cycas taitungensis and 56 protein-coding genes encoded in the cpDNA of Gnetum parvifolium. The cpDNA of Cycas is a circular molecule of 163,403 bp with 2 typical large inverted repeats (IRs) of 25,074 bp each. We inferred phylogenetic relationships among major seed plant lineages using concatenated 56 protein-coding genes in 37 land plants. Phylogenies, generated by the use of 3 independent methods, provide concordant and robust support for the monophylies of extant seed plants, gymnosperms, and angiosperms. Within the modern gymnosperms are 2 highly supported sister clades: Cycas-Ginkgo and Gnetum-Pinus. This result agrees with both the "gnetifer" and "gnepines" hypotheses. The sister relationships in Cycas-Ginkgo and Gnetum-Pinus clades are further reinforced by cpDNA structural evidence. Branch lengths of Cycas-Ginkgo and Gnetum were consistently the shortest and the longest, respectively, in all separate analyses. However, the Gnetum relative rate test revealed this tendency only for the 3rd codon positions and the transversional sites of the first 2 codon positions. A PsitufA located between psbE and petL genes is here first detected in Anthoceros (a hornwort), cycads, and Ginkgo. We demonstrate that the PsitufA is a footprint descended from the chloroplast tufA of green algae. The duplication of ycf2 genes and their shift into IRs should have taken place at least in the common ancestor of seed plants more than 300 MYA, and the tRNAPro-GGG gene was lost from the angiosperm lineage at least 150 MYA. Additionally, from cpDNA structural comparison, we propose an alternative model for the loss of large IR regions in black pine. More cpDNA data from non-Pinaceae conifers are necessary to justify whether the gnetifer or gnepines hypothesis is valid and to generate solid structural evidence for the monophyly of extant gymnosperms.     

暹罗苏铁茎的解剖学研究

利用冰冻切片法在光学显微镜下观察暹罗苏铁茎的解剖特征。结果表明,暹罗苏铁茎由周皮、皮层、皮层维管束、中柱和髓组成,皮层和髓发达。皮层维管束可分为周韧型和外韧型两种,以周韧型为主。中柱的次生结构为同心环的次生维管组织构成,随着茎的不断成熟,环数逐渐增加;每个同心环均含有次生木质部、维管形成层、次生韧皮部的结构;环与环之间有次生的薄壁组织相间隔。皮层、中柱维管束均由木质部、形成层和韧皮部组成,木质部面积均大于韧皮部。苏铁植物茎在次生结构方面的主要特点是有皮层维管束和同心环结构的中柱维管束。