探讨云南山茶起源的一线曙光—野生二倍体类型在金沙江流域的发现

新近发现的云南山茶原始二倍体类型分布于金江河谷流域的云南华坪悬及四川盐边县,海拔１８００－２８００ｍ。其植被模型为亚热带常绿阔叶林与云南松的混交林,生境较为湿润。云南山茶原始二倍体类型的形态特征与广布的六倍体类群非常相似,而与怒江山茶及西南山茶的形态特征不同。二倍体的花粉母细胞在减数分裂中期Ｉ形成１５个二价体,间期的细胞核结构为球形前染色体型,分裂前期染色体为中间型,其核型公式为２ｎ＝３０＝２２ｍ     

四倍体鲫鲤、三倍体湘云鲫染色体减数分裂观察

用精巢细胞直接制片法观察了异源四倍体鲫鲤、三倍体湘云鲫和二倍体红鲫、湘江野鲤精母细胞染色体第一次减数分裂中期配对情况 ;作为对照 ,观察了上述四种鱼肾细胞的有丝分裂中期染色体。在精母细胞第一次减数分裂中 ,异源四倍体鲫鲤同源染色体两两配对 ,形成 10 0个二价体 ,没有观察到单价体、三价体和四价体 ;三倍体湘云鲫精母细胞形成 5 0个二价体和 5 0个单价体 ;红鲫和湘江野鲤精母细胞分别形成 5 0个二价体。肾细胞检测表明异源四倍体的染色体数目为 4n =2 0 0 ;湘云鲫为 3n =15 0 ;红鲫和湘江野鲤分别为 2n =10 0。减数分裂时染色体分布情况与肾细胞染色体检测结果相吻合。具有四套染色体的异源四倍体鲫鲤在减数分裂中只形成 10 0个二价体 ,而不形成 2 5个四价体或其它形式 ,为产生稳定一致的二倍体配子提供了重要的遗传保障 ,也为人工培育的异源四倍体鲫鲤群体能够世世代代自身繁衍下去提供了重要的遗传学证据。三倍体湘云鲫在减数分裂过程中出现二价体、单价体共存 ,同源染色体在配对和分离中出现紊乱 ,导致非整倍体生殖细胞的产生 ,为湘云鲫的不育性提供了染色体水平上的证据     

拟南芥同源四倍体减数分裂过程的分子细胞学分析

以拟南芥(Columbia生态型)二倍体(AA,2n=10)为材料,经0.2%秋水仙素处理和细胞学鉴定,成功获得拟南芥同源四倍体(AAAA,2n=20)。以二倍体为对照,通过对拟南芥同源四倍体减数分裂过程染色体行为的观察,以及减数分裂调控同源染色体联会与重组相关基因的定量PCR分析,研究结果表明,与二倍体相比,拟南芥同源四倍体叶片表皮细胞间气孔孔径显著增大,荚果变长,但气孔密度和结实率显著降低;在减数分裂过程中出现部分单价体和三价体,以及二价体和四价体等染色体配对构型;减数分裂期重组相关基因ZYP1表达水平降低,ASY1、DMC1、MRE11和SPO11-1表达水平均升高。因此,我们推断,伴随着多倍体化,与二倍体相比,多倍体植物减数分裂期染色体行为和相关基因表达都有一定改变,影响多倍体植物生殖发育以适应环境。     

金沙江中游地区红山茶组植物的Giemsa C－带研究

研究了金沙江中游地区红山茶组植物的ＧｉｅｍｓａＣ－带。该地区的红山茶植物以四倍体为主,个别居群为二倍体或六倍体。居群间的Ｃ－带差异明显,Ｃ－带多出现在染色体端部。在四倍体和六倍体的Ｃ－带带型中,只能找到２条显相同Ｃ－带的同源染色体,通过与其它地区的红山茶植物进行比较,发现红山茶组植物的倍性从华东,华南经贵州,四川向云南逐渐增高,显Ｃ－带的染色体与染色体总数之比随信性增加而减少。文中指出华东或华南可能是红山茶组植物的起源地,而金沙江中游地区是其现代分化中心,这一地区红山茶的多倍体类群可能是异源起源的。     

玉兰减数分裂观察及染色体构型分析

采用去壁低渗方法,观察研究了玉兰Magnolia denudata有丝分裂和减数分裂的细胞学特征。实验结果证实玉兰存在两种染色体倍性,即2n=4x=76和2n=6x=114。通常,在木兰属甚至整个木兰科每个物种只具有一种染色体数目。玉兰有丝分裂间期核为复杂染色中心型,其中期染色体较小。玉兰在减数分裂中期I的构型表现出多样性,其中最主要的特点是比同源多倍体预期的二价体出现的频率更高些,其次是在减数分裂中期I可以观察到1或2个环状和（或）链状六价体。这些特征与同源异源六倍体或部分的异源六倍体种北美红杉Sequ     

六倍体多星韭的发现及多星韭种内倍性组成及演化的分析

采用染色体常规制片技术,对云南西北部和中部地区11个多星韭居群进行了细胞学分析。结果显示:(1)云南西北部多星韭二倍体、四倍体混合分布的太子阁和华首门四倍体居群中发现了三倍体(2n=3x=21),核型公式分别为:2n=3x=21=[6m(2sat)+8sm]+(3m+4sm)和2n=3x=21=[4m(2sat)+10sm]+(2m+4sm+lst)。三倍体含2条随体染色体,它的21条染色体含2个同源染色体组和一个与它们同源性稍差的染色体组。(2)在云南中部的多星韭四倍体居群中首次发现了六倍体,核型公式为2n=6x=42=15m(3sat)+27sm,核型类型2A。(3)结合核型特征及地理分布对多星韭三倍体和六倍体的成因进行分析,提示多星韭三倍体来源于二倍体与四倍体的杂交,六倍体是通过四倍体产生的未减数配子(n=4x=28)与正常减数配子(n=2x=14)的结合形成的。本研究结果支持多星韭的分化中心是云南西北部高海拔地区的观点,并结合前人的研究和本工作的结果,对多星韭种内的倍性组成和演化进行了分析和讨论。     

金沙江中游地区红山茶组植物的Giemsa C—带研究

研究了金沙江中游地区红山茶组植物的Ｇｉｅｍｓａ Ｃ一带。该地区的红山茶植物以四倍体为主,个别居群为二倍体或六倍体。居群间的Ｃ－带差异明显,Ｃ－带多出现在染色体端部。在四倍体和六倍体的Ｃ－带带型中,只能找到２条显相同Ｃ－带的同源染色体,通过与其它地区的红山茶植物进行比较,发现红山茶组植物的倍性从华东,华南经贵州,四川向云南逐渐增高,显Ｃ－带的染色体与染色体总数之比随倍性增加而减少。文中指出华东或华南     

一种新的六倍体细胞类型水生薏苡的细胞遗传学鉴定

通过醋酸洋红压片和荧光原位杂交技术(包括基因组原位杂交技术),确定在我国广西西南部地区广泛分布着的水生薏苡(Coix aquatica Roxb.)属于一种新的六倍体细胞类型.这种水生薏苡与已报道的几种水生薏苡细胞类型的染色体数目均不相同,它的染色体数目是2n=30,在减数分裂前期Ⅰ和中期Ⅰ的细胞中形成10个二价体和10个单价体.基因组原位杂交结果表明,这种水生薏苡的20条染色体与四倍体的薏苡(C.lacryma-jobi,2n＝20)的基因组DNA是高度同源的.45S和5S rDNA分别杂交到这种水生薏苡的两条染色体上,其中各有一条染色体与薏苡中携带45S和5S rDNA杂交信号的染色体具有相同的形状和信号的分布状态.据此推测:四倍体的薏苡可能是这种新的水生薏苡细胞类型的一个亲本,它的另一个亲本可能是八倍体的水生薏苡(C.aquatica,2n＝40),因为这种八倍体的水生薏苡在核型、植株形态及生长环境等方面与新的六倍体细胞类型的水生薏苡相似.     

一种新的六倍体细胞类型水生薏苡的细胞遗传学鉴定

通过醋酸洋红压片和荧光原位杂交技术(包括基因组原位杂交技术), 确定在我国广西西南部地区广泛分布着的水生薏苡(Coix aquatica Roxb.)属于一种新的六倍体细胞类型。这种水生薏苡与已报道的几种水生薏苡细胞类型的染色体数目均不相同,它的染色体数目是2n = 30,在减数分裂前期Ⅰ和中期Ⅰ的细胞中形成10个二价体和10个单价体。基因组原位杂交结果表明,这种水生薏苡的20条染色体与四倍体的薏苡(C. lacryma-jobi, 2n = 20)的基因组DNA是高度同源的。45S 和5S rDNA分别杂交到这种水生薏苡的两条染色体上,其中各有一条染色体与薏苡中携带45S和5S rDNA杂交信号的染色体具有相同的形状和信号的分布状态。据此推测: 四倍体的薏苡可能是这种新的水生薏苡细胞类型的一个亲本,它的另一个亲本可能是八倍体的水生薏苡(C. aquatica, 2n = 40), 因为这种八倍体的水生薏苡在核型、植株形态及生长环境等方面与新的六倍体细胞类型的水生薏苡相似。     

二倍体雌核发育鱼产生二倍体卵子的证据

二倍体雌核发育第 1代 (G1)产生的二倍体卵子经紫外线灭活的散鳞镜鲤精子诱导 ,无需染色体加倍处理 ,发育成二倍体雌核发育第 2代 (G2 ) ;G1 产生的二倍体卵子与雄性异源四倍体鲫鲤 (AT)产生的二倍体精子结合 ,形成新型两性可育的异源四倍体鲫鲤 (G1 ×AT)。对G2 和新四倍体 (G1 ×AT)的体细胞染色体数目、生殖细胞染色体行为及性腺结构、外形、生长速度等生物学特征进行了研究。结果表明 :G2 体细胞染色体数目为 2n =1 0 0。在 6～ 1 2月龄G2 中 ,没有发现性成熟的个体 ,组织学切片结果表明 ,G2 性腺处于卵原细胞增殖阶段 ,与 1龄G1 的性腺发育相似 ,性腺发育迟缓。对 6～ 8个月龄G2 性腺染色体制片进行观察 ,结果表明 ,G2 生殖细胞的染色体没有二价体的形成 ,只有有丝分裂的迹象 ,其有丝分裂中期不但有 2n =1 0 0的染色体分裂相 ,还有 4n =2 0 0的染色体分裂相 ,甚至有接近 8n(380 )的分裂相 ,说明 1龄G2 的性腺中存在 2n、4n等多种类型的生殖细胞 ,其中 4n的生殖细胞经正常的减数分裂后可产生二倍体卵子。核内复制 (pre meioticendoreduplication)学说可以较好地解释这种不减半配子产生的现象。新四倍体 (G1 ×AT)体细胞染色体数目为 4n =2 0 0 ,雌雄新四倍体 (G1 ×AT)具有正常的性腺发育 ,在繁殖季     

The Discovery of Tetraploid Camellia reticulata and Its Implication in Studies on the Origin of This Species

Camellia reticulata and its two allied species, C. saluenensis and C. pitardii,all from the Jinshajiang Valley of Yunnan and Sichuan, were cytologically studied in this work. Among 34 populations of C.reticulata studied here, 21 were found to be tetraploids (2n=60), 11 hexaploids (2n = 90), and the remaining two diploids (2n = 30). Tetraploid was reported in C. reticulata for the first time and its karyomophology was studied. In meiosis of pollen mother cells of the tetraploids and the hexaploids, only bivalents were observed in most of the populations, although in several populations or individuals a few univalents or tetravalents appeared. In the hexaploids, hexavalents were not observed. Thus, the meiotic chromosome cofigurations showed that the tetraploids and hexaploids in C.reticulata allopolyploids, and the appearance of a few tetravalents in some populations might indicatehomology of chromosomes in different genomes to some extent. The characteristics of the resting nuclei and the prophase chromosomes of all the tetraploids and hexaploids were quite similar to each other. The tetraploids of C.reticulata from the localities with the altitude of over 1800 m were gross-morphologically similar to the hexaploids, but those growing between 1100 ～1800 m were different to some extent from the hexaploids. In geographical distribution, the tetraploids and the hexaploids were continuous, and overlapped with C. saluenensis and C. pitardii.     

The origin and meiotic behaviour of hexaploid northern wheatgrass (Agropyron dasystachyum)

The occurrence of hexaploid (2n = 6x = 42) forms in some otherwise natural tetraploid populations of Agropyron dasystachyum (2n = 4x = 28) was cytologically detected and studied. The hexaploid plants are morphologically similar to the tetraploids except for a small reduction in the anther size. The general survey of chromosome numbers of natural Northern Wheatgrass (A. dasystachyum 2n = 4x = 28) populations derived from eight different regions of Alberta indicated that the occurrence of hexaploid variants was not restricted to a single locality. A comparative study of chromosome pairing in the natural and the synthetic hexaploids revealed that the naturally occurring 42-chromosomed plants of A. dasystachyum originated as a result of fertilization between unreduced (SSHH) and the natural (SH) gametes, both coming from the tetraploid form of A. dasystachyum. Based on chromosome pairing, the genomes of the natural hexaploid A. dasystachyum have been designated as SSSHHH. The natural hexaploids appear to intercross among themselves and also with tetraploids producing euploid and aneuploid hybrids. The possible evolutionary significance of these findings is briefly discussed.     

THE HORDEUM VIOLACEUM COMPLEX OF IRAN

Fifty-seven Iranian collections of Hordeum violaceum Boiss. & Huet, a perennial forage grass, contained diploid (2n = 14), tetraploid (2n = 28), and hexaploid (2n = 42) chromosome races. All collections came from moderate to high elevations in the Alborz and Zagros mountains and adjacent plateau areas of Iran. Each chromosome race had a discrete distribution, and the hexaploids were the most widespread. The diploids were cytologically regular, except for a chromosome interchange that occurred in about half of the plants. The tetraploids and hexaploids behaved cytologically as autopolyploids. The hexaploids were taller, coarser and later-flowering than the diploids and tetraploids, and they had fewer but thicker culms and larger seeds. The tetraploids were the leafiest and most productive, making them the most desirable from an agronomic standpoint. All races were more or less self-sterile, a characteristic that sets H. violaceum apart from most other Hordeum species. The taxonomic status of H. violaceum and its closest relatives, H. turkestanicum Nevski and H. brevisubulatum Link, is uncertain because of close morphological similarities and the occurrence of chromosome races in each taxon.     

Tempo and mode of recurrent polyploidization in the Carassius auratus species complex (Cypriniformes,Cyprinidae)

Polyploidization is an evolutionarily rare but important mechanism in both plants and animals because it increases genetic diversity. Goldfish of the Carassius auratus species complex can be tetraploids, hexaploids and octaploids. Polyploidization events have occurred repeatedly in goldfish, yet the extent of this phenomenon and its phyletic history are poorly understood. We explore the origin, tempo and frequency of polyploidization in Chinese and Japanese goldfish using both mitochondrial (mtDNA) and nuclear DNA sequences from up to 1202 individuals including the outgroup taxon, Cyprinus carpio. Analyses of de novo nuclear gene data resolve two clusters of alleles and the pattern supports the prior hypothesis of an ancient allotetraploidization for Carassius. Alleles shared by tetraploid and hexaploid individuals indicate recent autoploidizations within the C. auratus complex. Sympatric tetraploids and hexaploids share mtDNA haplotypes and these frequently occur independently within six well-supported lineages and sublineages on a small spatial scale. Gene flow estimates (F_st values) indicate that hexaploids differ only slightly from sympatric tetraploids, if at all. In contrast, allopatric populations of tetraploids and hexaploids differ from one another to a far greater extent. Gene flow between sampled localities appears to be limited. Coalescence-based time estimations for hexaploids reveal that the oldest lineage within any sampled locality is around one million years old, which is very young. Sympatric, recurrent autoploidization occurs in all sampled populations of the C. auratus complex. Goldfish experience polyploidization events more frequently than any other vertebrate.     

Phytogeographical studies ofCalamagrostis sachalinensis (Gramineae)

Chromosome numbers were determined on 223 collections ofCalamagrostis sachalinensis from 18 localities in Japan. The plants were found to be tetraploid (2n=28), hexaploid (2n=42) or octoploid (2n=56). A few collections were found to include one or two B-chromosomes. The tetraploid collections were made from central Honshu and Mt. Apoi in Hokkaido, while the hexaploids and the octoploids were detected in many localities. Pollen examination of these collections showed that the tetraploids with but one exception have good pollen and the hexaploids and the octoploids have no pollen or have bad pollen with stainability less than 10%. With the help of pollen examination of a number of herbarium specimens, the distribution of the tetraploids and that of the assemblage of the hexaploids and octoploids were delineated. Morphological studies indicated that the tetraploid, hexaploid and octoploid plants can not be separated in gross and spikelet morphology and that the tetraploids in central Honshu and those in Mt. Apoi are significantly different in leaf features. It was concluded thatC. sachalinensis represents an apo-amphimictic complex, which includes the following four races: 1) tetraploid, amphimictic, having thin leaf blades 5–10 mm broad and growing on the subalpine conifer forest belt and the conifer forest-alpine ecotone in the mountains of central Honshu; 2) tetraploid, amphimictic, having hard leaf blades 2–6 mm broad and growing on the stony, arid and exposed alpine belt on Mt. Apoi in Hokkaido; 3) hexaploid, mainly apomictic, the most variable ecologically, widely distributed; 4) octoploid, mainly apomictic, frequent in the upper montane to alpine belts, probably widely distributed.     

A cytotaxonomic study of theCalamagrostis purpurea —langsdorffii—canadensis complex in the lowlands of hokkaido

A chromosome survey of 278 individuals from 52 localities confirmed, that the principal components of theCalamagrostis purpurea—langsdorffi—canadensis complex in the lowlands of Hokkaido are tetraploid (2n=28) and octoploid (2n=56). A few hexploids (2n=42), were also found, but they may be either a triploid of the tetraploid plants or a hybrid between the tetraploid and octoploid plants. These hexaploids clearly differ in origin from the North American plants with 2n=42 which are generally placed underC. canadensis. The tetraploids and the octoploids are significantly different in pollen size but resemble each other in other morphological features and ecological requirements. These two races are also not disparate in distribution within Hokkaido. The tetraploids in Hokkaido are closely related to the tetraploids known in Alaska, and these tetraploid plants may be continuously distributed from Hokkaido to Alaska. The octoploids in Hokkaido have shown good pollen. They seem to have had a somewhat different course of evolution fromC. purpurea s. str. which principally reproduces in an apomictic manner.     

Cytogeography of the South American Turnera sidoides L. complex (Turneraceae, Leiocarpae)

New chromosome number determinations are presented for 48 populations of five subspecies of Turnera sidoides. Chromosome counts in sspp. carnea, holosericea, integrifolia and sidoides confirm previous data while, in ssp. pinnatifida , the numbers 2n=2x = 14 and 2n = 6x = 42 are reported for the first time. The results show that polyploidy is a very frequent phenomenon. Populations are primarily tetraploids (2n = 4x = 28), while diploids (2n = 2x = 14), hexaploids (2n = 6x =42) and octoploids (2rc = 8x = 56) are less frequent. Diploid, tetraploid and hexaploid cytotypes occur in sspp. carnea and pinnatifida , whereas tetraploids and hexaploids are known in ssp. holosericea. Turnera sidoides ssp. integrifolia shows a polyploid series with ploidy levels from 2x to 8x. The ssp. sidoides appears to be uniformly tetraploid, with the exception of an isolated pentaploid (2rc = 5x = 35). On the basis of these counts and previous reports the geographical distribution of the cytotypes has been determined and related to climatic and ecological factors.