中国柴胡属染色体数目和核型研究

采用植物染色体常规压片技术,报道了中国柴胡属(Bupleurum L .)13种5变种24个居群的染色体数目,其中4种5变种为首次报道,同时报道了5种1变种的细胞核型.除天山柴胡两个居群、紫花鸭跖柴胡一个居群和北柴胡一个居群是多倍体外,其它均为二倍体.主要结论如下:(1)秦岭柴胡和细茎有柄柴胡处理为独立的种更为合适;紫花阔叶柴胡作为大叶柴胡变种的处理是合理的;黄花鸭跖柴胡处理为紫花鸭跖柴胡的变种是不合理的.(2)紫花鸭跖柴胡和北柴胡可能都是还没有被完全认识的复合类群,需要进一步研究.(3)x=7可能是柴胡属的原始基数.     

Nuclear fusions contribute to polyploidization of the gigantic nuclei in the chalazal endosperm of<Emphasis Type="Italic"> Arabidopsis</Emphasis>

Somatic polyploidization is recognized as a means to increase gene expression levels in highly active metabolic cells. The most common mechanisms are endoreplication, endomitosis and cell fusion. In animals and plants the nuclei of multinucleate cells are usually prevented from fusing. Here, we report that the nuclei from the syncytial cyst of the chalazal endosperm of Arabidopsis thaliana (L.) Heynh. are polyploid with some intermediate ploidy levels that cannot be attributed to endoreplication, suggesting nuclear fusion. Analysis of isolated nuclei, together with fluorescent in situ hybridization (FISH), revealed that nuclei from the chalazal endosperm are two or three times bigger than the nuclei from the peripheral endosperm and have a corresponding increase in ploidy. Together with the consistent observation of adjoined nuclei, we propose that nuclear fusion contributes, at least in part, to the process of polyploidization in the chalazal endosperm. Confocal analysis of intact seeds further suggested that free nuclei from the peripheral endosperm get incorporated into the chalazal cyst and likely participate in nuclear fusions.Abbreviations BAC Bacterial artificial chromosome - CZE Chalazal endosperm - DAPI 4,6-Diamino-2-phenylindole - FISH Fluorescent in situ hybridization - NOR Nucleolar organizing region - NCD Nuclear cytoplasmic domain - PEN Peripheral endosperm     

Nuclear ploidy is contingent on the microtubular cycle responsible for plant cytokinesis

Summary. Division of the plant cell relies on the preprophase band of microtubules (PPB)-phragmoplast system. Cells of onion (Allium cepa L.) root meristems were rendered binucleate by preventing the consolidation of cell plate formation in telophase with 5mM caffeine. These binucleates developed either a single PPB around one of their two nuclei or two PPBs, one per nucleus, in the prophase of the ensuing mitosis. Prophase cells developing one single PPB were shorter in length (42.3±4.1µm) than those developing 2 PPBs (49.8±4.1µm), and interphase duration was inversely related to cell length. Cells whose length was less than or equal to 42µm, i.e., which had not even reached the mean size of the small binucleates in prophase, were followed throughout mitosis. In metaphase, they always assembled two mitotic spindles (one per nucleus). However, the cells that had assembled a single PPB also developed a single phragmoplast in telophase, leading to polyploidization. As these meristematic cells were not wide enough to accommodate the midzones of both mitotic spindles in any single plane transversal to the cell elongation axis, the spindles tilted until their midzones formed a continuum where the single common phragmoplast assembled. Its position was thereby uncoupled from that of the preceding PPB. Subsequently, the chromosomes from two different half-spindles were included, by a common nuclear envelope, in a single tetraploid nucleus. Finally, the cytokinetic plate segregated the two tetraploid nuclei formed at each side of the phragmoplast into two independent sister cells.Correspondence and reprints: Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain.     

Nuclear and cell fusion cause polyploidy in the megagametophyte of common cypress, Cupressus sempervirens L.

In common cypress, Cupressus sempervirens L., the megagametophyte persists in mature seeds as a polyploid endosperm containing cells with even and odd series of DNA contents: 1C, 2C, 3C, 4C, 5C etc., where C is the amount of DNA in the haploid genome. In this study, cytometrical, histological and cytochemical investigations were performed in order to determine the behavior of megagametophyte nuclei during the reproductive cycle. Unexpected nuclear alterations due to a continuous process of nuclear fusion were observed in the megagametophyte, leading to polyploidization and consequently to intense food-reserve synthesis. During the free nuclear stage, the megagametophyte exhibited only sporadic nuclear fusion and limited food-reserve production. When cellularization took place, multinucleated compartments were observed in which nuclei fused, producing odd and even series of DNA contents as proved by flow-cytometric analysis. This polyploidization process considerably increased after fertilization and during embryo development, and was accompanied by increased food-reserve synthesis. During these later stages, fusion mainly involved nuclei of contiguous cells and was preceded by the disintegration of their adjacent walls. Mitoses with incomplete phragmoplast differentiation were also observed to yield polyploid nuclei. Finally, in mature seeds the endosperm still exhibited multinucleate cells and fusion nuclei, and contained high amounts of storage products. The results are interpreted as an alteration of DNA contents in the megagametophyte cells in relation to specific metabolic activity during seed development. Received: 2 September 1998 / Accepted: 31 December 1998     

Binucleate cells in mouse morulae

Summary Mouse morulae from two strains were examined in whole mounts after dissociation of embryos into single cells and were analysed in serial sections by light and electron microscopy. One or two binucleate cells per embryo were discovered in a statistically significant number of morulae. The frequency of morulae with binucleate cell(s) was higher in older morulae than in younger ones. Binucleate cells were always the outer cells of the embryo. Their ultrastructure did not differ from the ultrastructure of mononucleate cells. It is suggested that cell binuclearity at the morula stage is a possible way to polyploidization of nuclei, resulting in the formation of primary trophoblast giant cells.     

分子标记所揭示的人工合成小麦与推广品种杂交后代中出现的新变异

杂交和多倍化是小麦进化和遗传分化的重要途径,新变异的产生为人工选育小麦新品种提供了物质基础。本文选用了分布于小麦A、B、D基因组的92个SSR标记对硬粒小麦-节节麦人工合成小麦衍生材料川W5436（CW5436）及其双亲人工合成小麦Syn786（♀）和绵阳26（My26（♂））进行了遗传分析,结果表明：人工合成小麦的各等位基因并不是按盂德尔遗传的规律传递到后代中;川W5436与双亲比较在1个SSR位点上发生了川W5436所特有的新变异,主要表现在新型DNA片段的增加,即W5436出现了双亲不具有的特殊条带。表明人工合成小麦与普通小麦杂交过程中通过人工选择的压力使双亲的遗传物质产生了偏态分离而且微卫星序列发生了改变。本文对杂交转育中SSR位点遗传分化在小麦进化中的作用等问题进行了讨论。     

Flow cytometric and karyological analysis of polysomaty and polyploidization during callus formation from leaf segments of various potato genotypes

Summary Flow cytometry and karyological analysis were used to study polysomaty and polyploidization during the first 15 days of callus formation in leaf segments from shoot cultures and greenhouse-grown plants of various lines and genotypes of Solanum tuberosum and S. phureja. The greenhouse-grown plants showed a higher degree of polysomaty (77% and 49% of polyploidized nuclei) than the shoot cultures (< 3%). During the in vitro culture period, polyploidization occurred through endoreduplication. Segments of the five shoot cultures showed up to 87%, 53%, 59%, 45% and 56% polyploidization, respectively; the DNA content of corresponding interphase nuclei amounted to 8C, 16C, 16C, 16C and 8C, and the chromosome numbers to 96. Segments from the two greenhouse-grown genotypes showed up to 87% and 84% polyploidization; the DNA content amounted to 32C and 16C, and the chromosome numbers to 192 and 96. The number of reduplication cycles was species-dependent; the degree of polyploidization was dependent on the initial ploidy level of the genotypes. Cell proliferation did not take place at a constant rate. The maximum frequencies of metaphases (52–171 per segment) occurred after 1 week of culture and were correlated with the ploidy level of the genotypes. Cells were triggered to mitosis rather than to endoreduplication. Cell cycles with normal monochromosomes could be shorter than 1 day, and those with diplochromosomes lasted at least 1 day. Polysomaty, degree of polyploidization and abnormal nuclear processes are discussed in relation to the origin of genetic instability early in culture.     

Breakdown of distyly in a tetraploid variety of <Emphasis Type="Italic">Ophiorrhiza</Emphasis><Emphasis Type="Italic"> japonica</Emphasis> (Rubiaceae) and its phylogenetic analysis

We examined the floral morph of tetraploid Ophiorrhiza japonica Blume var. amamiana Hatus. and diploid O. japonica var. japonica to elucidate the association of distyly and ploidy levels. Chloroplast DNA phylogeny was reconstructed to determine the number of tetraploidization events and floral morph shifts in O. japonica. All individuals of O. japonica var. amamiana proved to be long-homostylous, whereas O. japonica var. japonica was distylous with typical long- and short-styled flowers. Distyly is related to the ploidy level. The bagging treatment of flowers indicated that O. japonica var. amamiana is self-compatible and potentially automatically self-pollinating. In cpDNA sequencing analysis, no haplotype was shared between the two varieties. The cpDNA haplotype network displayed the monophyly of O. japonica var. amamiana, suggesting a single origin of this variety. Hence, both tetraploidization and the breakdown of distyly to homostyly in O. japonica var. amamiana likely occurred just once. Because O. japonica var. amamiana having the morphological and cytological entity is recognized as a single lineage and clearly separated from O. japonica var. japonica, this variety can be considered to be a distinct species. We therefore propose to raise O. japonica var. amamiana to the rank of species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Is hybridization involved in the evolution of the Chenopodium album aggregate? An analysis based on chromosome counts and genome size estimation

For our study of the Chenopodium album aggregate, we selected those species of Euroasiatic origin that represent the diploid–polyploid complex in Central Europe: C. album (6x), C. ficifolium (2x), C. opulifolium (6x), C. striatiforme (4x), C. strictum (4x) and C. suecicum (2x). We especially focused on (a) the origin of polyploid species and (b) the frequency of hybridization between species with different ploidy levels. We did not find any direct evidence of the existence of hybrids between two species with different ploidy levels within the C. album group. The sample/standard ratio of tetraploid and hexaploid species does not equal multiples of that of diploid species, which suggests that (i) tetraploids are not diploid autopolyploids and that (ii) hexaploids have not evolved from diploid species alone. Moreover, we have not found any hybrid plant either in the field or even in the offspring resulting from our experimental crosses. In view of these results, we adhere to the opinion that Chenopodium species do not hybridize freely across ploidy levels. Our analysis of DNA amounts, however, suggests that C. album is an allopolyploid that has arisen by hybridization between a diploid and a tetraploid species the identity of which is unknown.