Unusual microtubular cytoskeleton of apomictic embryo sac of Chondrilla juncea L.

Summary. The mature apomictic embryo sac of Chondrilla juncea is highly vacuolated and demonstrates a polarization similar to that of the amphimictic gametophyte. The microtubule cytoskeleton of this embryo sac is uncharacteristic and relatively weak. The microtubules are positioned along cell walls and resemble cortical microtubules of somatic cells. They do not form the parallel, brushlike structures observed around the filiform apparatus of synergids in the amphimictic embryo sac. In the apomictic embryo sac, the microtubules of both the egg cell and the central cell develop a cortical-like structure, which is entirely different from the radial arrangement observed around the nuclei in the amphimictic embryo sac. Correspondence and reprints: Department of Plant Cytology and Embryology, Jagiellonian University, Grodzka 52, 31-044 Kraków, Poland.     

Sexual tetraploid and apomictic pentaploid populations ofHieracium pilosella (Compositae)

Five species are recognized inHieracium subgen.Pilosella sect.Pilosellina Fries. Four are diploid (2x, 2n = 18), one (H. pilosella L.) is highly variable morphologically and cytologically (from 2x to 10x), in its mode of reproduction (self-incompatibility, agamospermy, amphimixis, apo-amphimixis) and in its hybridization pattern. A part of this huge agamic complex was analysed by comparing sexual 4x and apomictic 5x plants (crossing and germination experiments, measurements of vegetative reproduction by stolons etc.). In the experimental garden apomictic 5x produced more stolons than the sexual 4x plants and the total length of the stolons per rosette was greater. However, in nature, the competitive potential of the sexual plants seems to be higher, presumably as a result of the higher mortality of ramets in 5x. Sexual 4x plants often grow in dense and grazed grass vegetation, whereas 5x apomicts often occur in dunes with patchy vegetation. Apomicts produce more capitula per rosette, and sexual rosettes form only about 60% of the number of viable achenes as compared to apomictic ones. Therefore, apomicts appear to be characterized by a greater colonizing ability than sexual plants. Apomictic plants produce equal numbers of viable achenes under conditions of both open pollination and isolation. Sexual plants do not form any viable achenes after isolation and produce a somewhat lower percentage of achenes after open pollination than do apomictics. 5xreproduce exclusively apomictically. Apo-amphimixis was never observed in pentaploids and only very rarely in tetraploids. Addition hybrids are very rare. The cross sexual 4x × apomictic 5x failed in 70% of the attempts, but the recombination of genomes carrying genes for apomixis is possible and results in apomictic 4x and sexual 5x, both with a reduced number of viable achenes. In nature sexual and apomictic plants may occur in close proximity. In such cases the germination rate of the achenes of 4x and 5x is lower; this may indicate that apomictic plants fertilize sexual plants in nature (unidirectional gene-flow). 5x plants form euploid gametes carrying two or three genomes. The results of the crossing experiments can be explained in terms ofNogler's theory of monogenic inheritance of apospory.Variation and evolution inHieracium subg.Pilosella sect.Pilosellina I.     

A compound capitulum in Melampodium L. (Compositae)

The involucre of each female ray floret of Melampodium, as revealed by its anatomy, is found to be formed by the fusion of two bracts. The inflorescence in this genus is, therefore, actually a compound head with several uniflorate female capitula surrounding a central multiflorate male capitulum. It is not a simple head as is usually described.     

The tribal position of Oedera L. (Compositae)

l position of Oedera L. (Compositae). The South African genus Oedera L. (Compositae-Anthemideae) is shown to be closely related to the South African genera Relhania and Leysera . A transfer of Oedera from the tribe Anthemideae to the tribe Inuleae is proposed. Several synapomorphies, like a two-layered sexine, concave leaves, pappus of connate scales, long and slender cypselas define the monophyletic group. The pollen-wall morphology of Oedera is described and the chromosome number 2 n = 14 is reported.     

千里光合子胚和胚乳形成及其早期发育的细胞学特征(英文稿)

千里光（Senecio scandens Buch.-Ham. ex D. Don）是传统中草药, 抗菌功效显著。本研究从细胞学角度对千里光合子胚和胚乳的形成与发育进行观察研究。结果显示,结构和功能迥异的基细胞和顶细胞源自细胞质不均一分布的合子所致,推测合子的极性与胚囊的极性和生殖核分裂为“二态”精细胞有关;基细胞在合子胚胎“球型期”末期出现分化,早期胚胎的组织分化始于“三角期”,可辨别的结构差异直到“鱼雷期”才出现。此外,胚乳形成遵循无细胞壁核化模型。本研究对千里光细胞分化、组织分化和结构差异各发育阶段特征的观察结果,不仅可为深入分析胚胎发育过程功能基因的时空表达提供依据,也为相关近缘物种的系统植物学研究提供参考资料。     

千里光合子胚和胚乳形成及其早期发育的细胞学特征（英文）

千里光(Senecio scandens Buch.-Ham. ex D. Don)是传统中草药,抗菌功效显著。本研究从细胞学角度对千里光合子胚和胚乳的形成与发育进行观察研究。结果显示,结构和功能迥异的基细胞和顶细胞源自细胞质不均一分布的合子所致,推测合子的极性与胚囊的极性和生殖核分裂为二态精细胞有关;基细胞在合子胚胎球型期末期出现分化,早期胚胎的组织分化始于三角期,可辨别的结构差异直到鱼雷期才出现。此外,胚乳形成遵循无细胞壁核化模型。本研究对千里光细胞分化、组织分化和结构差异各发育阶段特征的观察结果,不仅可为深入分析胚胎发育过程功能基因的时空表达提供依据,也为相关近缘物种的系统植物学研究提供参考资料。     

Zur Polyploidie in der Gattung Centaurea L. Sektion Acrocentron (Compositae)

1. Folgende Centaurea-Sippen aus der Sektion Acrocentron wurden cytologisch untersucht: C. graeca (2n = 20), C. spruneri s. str. (2n = 110), C. guicciardii s. str. (2n = 100, 2n = 110), C. guicciardii var. lineariloba (2n = 20) und C. salonitana var. subinermis (2n = 40). Die Chromosomenzahlen der ersten drei genannten Arten werden zum erstenmal mitgeteilt. 2. Das Phänomen der Polyploidie innerhalb der Sektion Acrocentron wird kurz diskutiert. Die Basiszahl von × = 10 für diese Sektion wird bestätigt.     

Fruit morphology in Tragopogon L. (Compositae: Lactuceae) from the Iberian Peninsula

Achenes of all the Tragopogon species from the Iberian Peninsula were examined by means of scanning-electron microscopy and stereomicroscopy. The achenes of the eight species are described, illustrated and compared. The results are contrasted with the systematics of this genus. The isolated position of T. lamottei with regard to the other seven species is noted. A key is provided to enable the different species to be distinguished.     

苦瓜胚胎学研究

以石蜡制片法对苦瓜(Momordica charantia L.)进行了胚胎学研究。小孢子母细胞减数分裂时,胞质分裂为同时型,形成四面体型四分体和左右对称型四分体。成熟花粉为二细胞型。子房三室,双珠被,厚珠心,倒生胚珠。大孢子四分体为线形,合点端功能大孢子发育成为蓼型胚囊。中央细胞细胞质中有大量贮藏物质存在。极核在受精时融合。双受精过程属有丝分裂前配子融合类型。3个反足细胞随受精过程进行而退化。胚胎发生为柳叶菜型。核型胚乳,合点端具胚乳吸器。     

Origin of the serpentine-endemic herb Layia discoidea from the widespread L. glandulosa (Compositae)

Phylogenetic analyses of nuclear rDNA sequences uphold Gottlieb et al.'s hypothesis that Layia discoidea, a morphologically unusual, serpentine-endemic herb of narrow distribution in central California, "budded off" recently (less than one million years ago) from a nearby lineage of the widespread L. glandulosa, which occurs on sandy soils across much of far western North America. Although L. discoidea and L. glandulosa retain complete interfertility, nuclear rDNA data for the two species are almost free of evolutionary noise, without evidence of gene flow between them; allopatric divergence of L. discoidea cannot be ruled out. Molecular data are consistent with a hypothesis of accelerated morphological evolution of L. discoidea and Gottlieb et al.'s suggestion that the closest relatives of L. discoidea are populations of L. glandulosa with yellow, rather than white, ray corollas, in accord with Clausen, Keck, and Hiesey's evidence of a gene for yellow ray coloration in the rayless L. discoidea.     

Structure and development of sperm bundles in the dragonfly Aeshna juncea L. (Odonata)

A re-examination of the origin and development of sperm bundles in aeshnid dragonflies (Odonata, Anisoptera) was carried out using light and electron microscopy. During their elongation, intracyst spermatids of the testis of the dragonfly Aeshna juncea L. form a slender cytoplasmic protrusion, the acrosomal conicoid, beyond the nucleus and acrosome rodlet. Gathering and parallel alignment of the transforming spermatids into a tight bundle take place inside the cyst. The original, rigid spermatid foreparts eventually associate, initially by becoming adhesive and swelling progressively to intertwine, and thus come to constitute a cap that binds together all sperm heads within a cyst in a spermatodesma. The development of the spermatodesma seems to occur disjunct from somatic cyst cells. Bundled in this form, the sperms are transferred to the intratestis canal and moved down the spermiduct to the seminal vesicle. They are then forwarded to the male copulatory apparatus, from which they are transmitted to the female. Individual, fully formed sperms are seen to be liberated from the bundle when in the female receptaculum seminis. The remnant of the cytoplasmic acrosomal conicoid, which is considered an envelope of the acrosome rodlet, is then dissolved. The spermatodesmata are large sperm aggregates that constitute efficient vehicles for transmission of amounts of filamentous sperm to the female. J. Morphol. 235:239–247, 1998. © 1998 Wiley-Liss, Inc.     

Somatic embryogenesis and plant regeneration in Cichorium intybus L. (Witloof,Compositae)

Somatic embryogenesis of Cichorium intybus L. var. Carolus is induced using cubical pieces of mature tap roots with an intervening callus phase. A Murashige and Skoog's (MS) semi solid basal medium supplemented with 2,4-dichlorophenoxyacetic acid (0.02 or 0.2 mg/l) and benzylaminopurine (0.25 mg/l) and a liquid MS medium devoid of growth regulators are used respectively for induction of callus and somatic embryoids and for further development and germination. Regeneration from the nodular proembryonal stage to the full grown embryoids occurs following different morphological pathways depending on the physical and chemical environment of the culture. Further development of these embryos into plantlets and the possibilities of application of this technique in plantbreeding have been discussed.Abbreviations MS Murashige and Skoog medium - BAP benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid     

Photoperiodic responses ofXanthium strumarium L. (Compositae) introduced and indigenous in eastern asia

Photoperiodic responses among populations ofXanthium strumarium L. in eastern Asia from Vladivostok, USSR, to Hong Kong and Taiwan include a wide range of adaptation. Among indigenous populations of thestrumarium morphological complex, responses range from near day neutrality (Vladivostok) to approximately a night length requirement of 9.5 hr (Hong Kong). Introduced populations in Japan include a night length requirement of 9.75 hr in theitalicum morphological complex and of 10.25–10.5 hr in thechinense morphological complex. The range of photoperiodic adaptation is nearly as wide as among populations of North America.     

Reproduction and perennation of Chondrilla juncea L. (skeleton weed) in the Western Australian wheatbelt

Survivorship of first-year plants of Chondrilla juncea was considerably higher on a deep yellow sand than on a yellow duplex soil. Mortality on the latter soil was associated with drying of the Al horizon during early summer. No plants produced seeds in their first year of growth on the duplex soil. However, during both years of the study, first-year individuals of both forms of C. juncea produced viable seeds when growing on the deep sand. Higher population growth rates could be expected on deep sands, owing to a combination of earlier reproduction and greater survivorship through the first summer. It is suggested that whilst the entire wheatbelt might be climatically suitable for C. juncea, the invasive potential of this weed might be restricted by edaphic characteristics over large areas.     

Gynodioecy in Cirsium chikushiense Koidz. (Compositae)

A study of the morphology and function of flowers in Cirsiumchikushiense revealed that the species was distinctly gynodioecious.Self-incompatible hermaphrodite florets produced both seedsand pollen grains, while female ones produced seeds but no pollengrains at all. The degenerated stamens of females were not onlysmaller but also sometimes occurred at a lower position insidethe floral tube than in hermaphrodites. The stigmata of femalesoften developed more fully than those of hermaphrodites. Thefrequencies of female plants in natural populations varied from15·5 to 50%. Almost all the pollinators stayed on bothfemale and hermaphrodite heads only to collect nectar. The femaleplants of this species may be more specialized in their genderby saving the cost of not only pollen grains but also stamens,and may be maintained by sufficient pollinators in natural populations.This gynodioecy may provide an example of nuclear-cytoplasmicmale sterility.Copyright 1994, 1999 Academic Press Sex expression, gynodioecy, Cirsium chikushiense, Compositae, male sterility, degenerated stamen, female frequency     

苦瓜胚胎学研究

以石蜡制片法对苦瓜(Momordi cacharantia L.)进行了胚胎学研究。小孢子母细胞减数分裂时,胞质分裂为同时型,形成四面体型四分体和左右对称型四分体。成熟花粉为二细胞型。子房三室,双珠被,厚珠心,倒生胚珠。大孢子四分体为线形,合点端功能大孢子发育成为蓼型胚囊。中央细胞细胞质中有大量贮藏物质存在。极核在受精时融合。双受精过程属有丝分裂前配子融合类型。3个反足细胞随受精过程进行而退化。胚胎发生为柳叶菜型。核型胚乳,合点端具胚乳吸器。     

Embryological study on gynogenesis in onion (Allium cepa L.)

Haploid induction in onion can, to date, be induced only via gynogenesis by culturing unfertilized flowers, ovaries or ovules. The process of haploid embryo induction has been macroscopically well studied, but only limited data exist from microscopic examination of ovule development status at the inoculation stage and of the origin of gynogenic embryos. Microscopic studies were carried out using individual donor plants with relatively high embryo induction frequencies (45.9 embryos formed per 100 flowers, on average, for 2 years). Ovaries from flower bud culture were fixed at 1 week intervals up to the 7th week of culture. These were compared with pollinated ovaries at 1 or 2 weeks after pollination. In total, 1428 unfertilized embryo sacs were examined. The results indicate that, at the time of inoculation, ovules within ovaries 2.0–3.0 mm in diameter contained two- or four-nucleate embryo sacs in the smallest ovaries to mature embryo sacs in the largest ovaries. It seems likely that the embryos are actually induced from ovaries cultured at the immature stage. After 1 or 2 weeks in culture, the egg apparatus primarily consisted of distinctly enlarged synergids and the egg cell, which was often detached from the micropylar pole. But free nuclear endosperm was also formed. From the 2nd to 7th week in culture, formation of haploid embryos (from globular to the almost mature cylindrical stage) was detected in 5.7% of the ovules. Their origin, for several reasons, was most likely the egg cell. In addition, ovules containing endosperm only (3.6%) and ovules containing the egg apparatus (0.5%) or both endosperm and embryo (0.4%) were detected. This observation is probably unique and has not yet been reported in other species studied. Received: February 2001 / Revision accepted: 20 April 2001     

Different effects of variation in Xanthium strumarium L. (Compositae) on two insect seed predators

Summary To determine the relative importance of variation in several plant characters on susceptibility to herbivores, we examined patterns of seed predation by two monophagous insect species and patterns of variation in ten populations of the cocklebur, Xanthium strumarium. Multiple regression analysis disclosed that one seed predator was most influenced by plant chemical variation, the other was significantly influenced by both chemical and morphological variation, but variation in yet another character, general burr size, was most important in conferring resistance to both insects simultaneously. The plant populations differed most in this character. Although many of the plant characters were correlated with each other, those important in determining susceptibility to each insect species were uncorrelated and independent of those conferring resistance to both insects simultaneously.These results imply that ecological similar herbivores may be influenced by different aspects of plant variation, and that predictions of evolutionary responses of local plant populations to herbivory may require knowledge of the structure of local herbivore communities and the dynamics of their establishment.     

Dormancy and dispersal in dimorphic achenes of tansy ragwort,Senecio jacobaea L. (Compositae)

Summary Marginal and central florets of the capitula of tansy ragwort Senecio jacobaea yield different kinds of fruit. The central (disk) achenes are lighter (x±SE=199±5g), more numerous (x±SE=58±0.6 achenes per head), and are equipped with a pappus aiding wind transport and rows of trichomes aiding animal transport. The marginal (ray) achenes are heavier (x±SE=286±7g), less numerous (virtually invariant at 13 achenes per head), and lack dispersal structures. Whereas disk achenes are relased shortly after they mature, ray achenes are retained by the parent for a period of months following maturity.Germination at constant temperature (20°C) and with alternating light (12 h light: 12 h dark) demonstrated that disk and ray achenes exhibit different germination syndromes. Germination percentage increases linearly with achene fresh weight in both types; for a given weight, disk achenes have a higher germination percentage than ray achenes. Germination time decreases with increasing achene weight in disk achenes, but increases with achene weight in ray achenes.The germination percentages and germination times for disk and ray achenes diverge progressively with increasing achene weight. The divergence in behavior is a result of diverging patterns of dry matter allocation in the two achene types. Increase in the size of disk achenes favors the embryo fraction, thereby speeding germination while reducing protection. Increase in the size of the ray achenes favors the pericarp fraction, thereby increasing protection while delaying germination.Reduced germination percentage and germination speed of the ray achenes were shown by experimental manipulation to be caused by physical inhibition by their thicker pericarps.Dimorphism in ragwort likely speards germination out in space and time, thereby increasing the number of safe sites an individual parent can exploit in disseminating offspring. The syndrome in other heteromorphic composites resembles that of ragwort, generally combining reduced dispersal-delayed germination in the outer achenes and distance dispersal-quick germination in the central achenes. The outer achenes are generally less numerous and larger. Dispersal traits (large numbers, early release and light wieght) are the direct opposite of dormancy traits (small numbers, delayed release and heavier weight). Thus conflicts between the properties determining dormancy and dispersal appear to require separate dormancy and dispersal phenotypes.