蕨受精作用的细胞学观察

为了阐明进化蕨类受精作用的特点和细胞学机制,该文采用透射电镜观察了蕨(Pteridium aquilinum var.latiusculum)受精作用的主要过程,观察结果显示:(1)蕨精子通过受精孔进入卵细胞,多数情况下,该精子的螺旋运动先在受精孔的下方产生一个受精腔,然后精子再与卵细胞质融合。(2)第一个精子的这种延迟的螺旋运动和因精子的钻入而引起的卵细胞固缩反应可能是阻止多精受精的重要因素。(3)卵发育时期产生的核外突在受精后仍能持续12 h,然后与核本体分离,逐渐在细胞质中消解。(4)合子通过其后方细胞质的液泡化而建立了水平极性,此后再进行细胞分裂。该研究观察到了进化蕨类受精作用过程中的一些新现象,包括产生受精腔、卵细胞固缩反应、核外突的命运以及合子极性建立等,这有助于理解蕨类植物的受精作用机制及有性生殖的演化。     

Comparative spatial distribution, size, biomass and growth rate of two varieties of bracken fern (Pteridium aquilinum L. Kuhn) in a neotropical montane habitat

A comparative field study of caudatum and arachnoideum, the two Pteridium aquilinum varieties of the caudatum subspecies known to grow in the neotropics, was performed in a montane savanna habitat of the Venezuelan Andes that was affected by wildfire. Frond size, ramet density and spatial distribution, blade and rhizome biomass, and frond elongation and expansion rates were measured in separate, isolated stands each containing only one bracken variety and covering approximately the same area (540 m²). In addition to clearly discernible morphological differences, caudatum and arachnoideum were found to possess distinct features: caudatum tends to develop open stands of relatively shorter blades of 76.6±0.89 cm (±SE) of rachis length and lower ramet density (1.6 fronds m^-2, max.=7 fronds m^-2) whereas arachnoideum grows into longer, more expanded fronds 124±1.6 cm tall and significantly higher ramet density (5.1 fronds/m², max.=14.6 fronds m^-2). The sum of aerial and underground biomass was found to be notably larger for arachnoideum (8522±614 Kg/ha) than for caudatum (1929±131 Kg ha^-1) in stands growing under the same habitat conditions. Therefore the spatial distribution of arachnoideum appeared considerably more compact than that of caudatum. Blade growth rates and development time were also very different. Newly emerged caudatum croziers developed into mature blades within 42 to 48 days following an inverse exponential curve whereas arachnoideum blades required 70 to 75 days to reach maturity following a linear development. All the above dissimilarities are interpreted as the hitherto unreported indication of diverging growth strategies of two cohabitant bracken varieties following fire.     

Recovery of Moorland Vegetation after Aerial Spraying of Bracken (Pteridium aquilinum (L.) Kuhn) with Asulam

Bracken (Pteridium aquilinum) is a major weed of seminatural vegetation in Great Britain, as in many other countries. As a consequence, large areas have been subject to control with the intention of restoring the former vegetation. The use of aerial spraying with asulam, a narrow spectrum, carbamate herbicide, has become a common method of control. However, its long‐term efficacy has not been assessed in terms of either controlling the bracken or in producing suitable restored habitats. This study undertook such an assessment by comparing the results of a 2002 survey of the sites subject to bracken control by aerial spraying of asulam with previous (1990/1991 and 1994) surveys of the same sites. This showed that a single application of asulam was effective in eradicating bracken (<1% cover remaining) on a third of sites. However, on 10% of the sites, the bracken had regenerated completely (cover >80%) and on the remainder it was still present in patches (>20% of quadrats), often at high density. More than half the sprayed sites had seen good recovery of moorland vegetation, the target of the restoration, because they were now classified as having upland heathland vegetation within the National Vegetation Classification. Considerable amounts of bracken control are grant aided as part of agri‐environment schemes. These schemes should be adapted to encourage good practice, namely, intensive follow‐up treatment by spraying any emerging fronds, and to encourage treatment of previously sprayed areas rather than spraying of new areas in order to protect previous investment of grant aid.     

Bracken (Pteridium aquilinum)-induced DNA adducts in mouse tissues are different from the adduct induced by the activated form of the Bracken carcinogen ptaquiloside

Following treatment with bracken fern (Pteridium aquilinum) extract and bracken spores a number of DNA adducts were detected by (32)P-postlabeling. Three of these adducts have been described previously (Povey et al., Br. J. Cancer (1996) 74, 1342-1348) and in this study, using a slightly different protocol, four new adducts, with higher chromatographic mobility, were detected at levels ranging from 50 to 230% of those previously described. When DNA was treated in vitro with activated ptaquiloside (APT) and analysed by butanol extraction or nuclease P1 treatment, only one adduct was detected by (32)P-postlabeling. This adduct was not present in the DNA from mice treated with bracken fern or spores, suggesting either that bracken contains genotoxins other than ptaquiloside or that the metabolism of ptaquiloside produces genotoxins not reflected by activated ptaquiloside. However, as the ATP-derived adduct has been detected previously in ileal DNA of bracken-fed calves, species-specific differences in the metabolism of bracken genotoxins may exist, thereby leading to differences in their biological outcomes.     

Observations on the Microanatomy of the Spermatozoid of the Bracken Fern (Pteridium aquilinum)

Salient features of structure of the spermatozoid of a fern (Pteridium aquilinum) have been determined by a combination of visual and ultraviolet microscopy, with electron microscopy of shadow-cast whole mounts and thin sections, using magnifications up to but not exceeding 50,000 diameters. Attention has been concentrated on the arrangement rather than on the internal details of the various parts. The most important component, apart from the spirally wound nucleus, numerous (about 40) cilia, and mitochondria, is a sheet of parallel fibres spirally wound near the surface of a cone of cytoplasm to which all the other major components are in various ways attached. The diameter of the individual fibres is of the order of 200 A. A few details are given of other minor cell constituents including additional mechanical materials, starch-containing leucoplasts, and the smaller cytoplasmic inclusions.     

The Effect of Colchicine on Spermatogenesis in a Fern, Pteridium aquilinum (L.) Kuhn

Treatment of developing antheridia of Pteridium aquilinum for24 h with radioactive and normal colchicine resulted in spermatocyteswith restitution nuclei, binucleate spermatocytes with multipleimmature blepharoplasts, and spermatids in which the organizationof the microtubular ribbon and basal bodies, and the shapingof the nucleus were seriously disturbed. The results indicatethat the coiling of the multilayered structure and the condensationof the chromatin, two key events in spermatogenesis, are independentof tubulin polymerization. Transitional stages were observed between the granular materialof the blepharoplast and microtubules. Colchicine affected theassembly of the cartwheel structure of the basal bodies lessthan that of the triplets, which were often rudimentary or absent.Autoradiographs were only partially successful because of thefailure to devise a satisfactory method of embedding by freeze-substitution,but there was clear evidence of colchicine binding by nucleiin young spermatocytes. Pteridium aquilinum (L.) Kuhn, bracken, spermatogenesis, colchicine     

蜈蚣草孢壁发育及其系统学意义

利用光镜、扫描电镜和透射电镜对凤尾蕨科(Pteridaceae)蜈蚣草(Pteris vittata L.)孢壁的形成和发育进行研究。结果表明:蜈蚣草孢子四面体型,极面观钝三角圆形,赤道面观半圆形或超半圆形,近极面具瘤状纹饰和近极脊,远极面具脊并连成网状,具赤道环;孢子具乌毛蕨型外壁,由外壁外层构成纹饰的轮廓;实心型周壁由2层构成,且内层薄、外层具小球体。结合孢子外壁和周壁的发育特征,认为凤尾蕨科与裸子蕨科和水蕨科的亲缘关系较近,支持将裸子蕨科和水蕨科置于凤尾蕨科。     

Micromorphological and chemical characterisation of Stachys recta L. subsp. serpentini (Fiori) Arrigoni in comparison to Stachys recta L. subsp. recta (Lamiaceae)

Stachys recta L. is a very polymorphous species in which numerous subspecies were recognised. S. recta L. subsp. serpentini (Fiori) Arrigoni is a typical endemism growing on serpentine soils in northern Apennines and particularly in Tuscany (Italy). In order to contribute to a better knowledge of this plant and to its differentiation with respect to S. recta L. subsp. recta, the micromorphological characters (non-glandular and glandular trichomes) and the essential oil composition of the two subspecies were investigated. Micromorphological characters were studied using scanning and transmission electron microscopy, while light microscopy was used for histochemical observations. Essential oil analysis was carried out by gas chromatography and mass spectrometry.In the two examined taxa, the morphology and distribution of glandular and non-glandular trichomes, and the different essential oil composition, may be considered distinctive characters at subspecies level. This is consistent with the taxonomic classification considering S. recta subsp. serpentini a subordinate taxon of S. recta.     

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment (sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.     

Molecules and Morphology: Conflicts and Congruence within the Fern GenusTrichomanes(Hymenophyllaceae)

The interaction between three independent data sets (anatomy/morphology, cytology, molecules) has been evaluated within the controversial genusTrichomanes(Hymenophyllaceae). Anatomy/morphology, cytology, andrbcL sequences, despite their high and significant level of incongruence, were thus empirically combined with differential weighting in a cladistic analysis withinTrichomanesin order to give an appreciation of the contribution of each data set in the resulting topologies and to study more precisely the nature of potential conflicts. Results show that any standard statistics values (such as bootstrap) do not appear to be objectively useful for the choice of the “best” topology or the “good” clades provided by the combination. This weighting approach reveals three cases: (i) some clades (such as subgenusDidymoglossum) are always retrieved and correspond to the absence of conflicts between the different data, (ii) some new clades (such as subgenusAchomanes) are either provided or reenforced as a “synergetic” result of the combination of the data and (iii) that remaining conflicting clades reflect the persistence of incongruence between data whatever the weighting.     

Morphological, chemical and genetic differentiation of two subspecies of Cistus creticus L. (C. creticus subsp. eriocephalus and C. creticus subsp. corsicus)

Cistus creticus L., an aromatic species from the Mediterranean area, contains various diterpenes bearing the labdane skeleton. The production of essential oil from this species has potential economic value, but so far, it has not been optimized. In order to contribute to a better knowledge of this species and to its differentiation, the morphological characters, volatile chemical composition and genetic data of two subspecies (C. creticus subsp. eriocephalus and C. creticus subsp. corsicus) were investigated. The leaf trichomes were studied using scanning electron microscopy. The chemical composition of Corsican essential oil (C. creticus subsp. corsicus) has been reported using GC, GC/MS and ¹³C NMR; the main constituents were oxygenated labdane diterpenes (33.9%) such as 13-epi-manoyl oxide (18.5%). Using plant material (54 samples) collected from 18 geographically distinct areas of the islands of Corsica and Sardinia, the basis of variation in the headspace solid-phase microextraction volatile fraction and an inter-simple sequence repeat genetic analysis were also examined. It was shown that the two subspecies of C. creticus differed in morphology, essential oil production, volatile fraction composition and genetic data.     

Achene morphology and slime structure in some taxa of Artemisia L. and Neopallasia L. (Asteraceae)

We have examined slime cell distribution on the surface of the achenes of some Artemisia and Neopallasia taxa, as well as slime composition, envelope formation during the hydration, and slime relation to different morphological features and environmental factors. The results of the studies show a characteristic pattern of slime cells distribution, which could differ between taxa. The slime in the taxa studied belongs to the cellulose type and consists of two components i.e., pectins and cellulose. Although all fruits contain slime cells, not all of them show the slime envelope formation. Plants occurring in dry habitats (such as A. barrelieri) or annual species (such as A. annua) are characterised by a large amount of slime and a fast process of slime envelope formation. Slime production has not been observed in some polyploid populations (A. campestris and A. campestris ssp. sericea) and in two species occurring in relatively fertile habitats (A. verlotiorum, A. vulgaris). A reason for this may be either the immaturity of polyploid fruits leading to the production of a scarce, not detectable slime amount or, alternatively, the occurrence of not functional slime cells. Slime facilitates and stimulates the germination, as well as the adherence of the fruits to the ground or to animals (for dispersal). The slime could play important role in the distribution and colonisation of new habitats in many Artemisia taxa.     

Aspects of Morphogenesis in a Dorsiventral Fern, Pteridium aquilinum (L.) Kuhn: With one Plate and ten Figures in the Text

The formation of the horizontal dorsiventral rhizome of Pteridiumaquilinum from the erect radial axis of the young sporelingis described. The shoot apex and the inception of leaves andbuds at the apical meristem have been investigated, and theirinception is shown to be essentially similar in long and shortshoots, later differences being due to differing rates of growthand internodal elongation in the two types of shoot.     

阔鳞瘤蕨(水龙骨科)卵细胞发育超微结构观察

水龙骨科是蕨类植物中最进化的类群,该文采用超微技术对水龙骨科的阔鳞瘤蕨(Phymatosorus hainanensis)卵发育过程进行观察,以完善薄囊蕨植物卵发生的资料,为揭示蕨类植物的有性生殖及演化机制奠定基础。结果表明:(1)幼卵、颈沟细胞、腹沟细胞通过胞间连丝紧密连接。(2)发育过程中,卵与腹沟细胞之间细胞壁显著加厚,将卵细胞与腹沟细胞隔离。(3)在壁的下方产生分离腔,内含大量不定形物质,但卵细胞与腹沟细胞在中间处始终相连。(4)分离腔中的不定形物质沉积在卵细胞质膜外形成了一层加厚的卵膜,而在连接区(孔区)处不形成卵膜,该位置最终形成了受精孔。(5)卵细胞核变得高度不规则,近成熟时卵核产生了大量的核外突。     

Food cues and gonadal development in neotropical spotted antbirds (Hylophylax naevioides)

Most temperate-zone birds live in environments with a regular seasonality, and primarily use the long-term changes in photoperiod as a cue to initiate gonadal development in anticipation of the breeding season. Short-term cues such as food and temperature are later used to fine-tune the rate of gonadal development to local conditions. Many tropical habitats are seasonal, but the timing of the seasons (e.g., rainy season) can vary considerably between years. We hypothesize that to time breeding in environments with seasonal variability, tropical birds respond to both long-term and short-term environmental cues to initiate gonadal growth. We tested the effectiveness of photoperiod and food cues for the initiation of gonad growth in captive male spotted antbirds (Hylophylax n. naevioides) from Panama. A ‘control’ group was maintained on the short natural photoperiod of 12 h light and 12 h dark (LD 12:12) and adequate food. A ‘food-stimulated’ group was also held on LD 12:12 but received an increase in food quantity and quality. A ‘photo+food-stimulated’ group experienced an increase in daylength by 1 h (LD 13:11, the maximal photoperiod in Panama) and an increase in food quantity and quality. Within 3 weeks testis sizes of ‘food-stimulated’ birds increased significantly, suggesting that food cues alone can initiate gonad development. As expected from the previous experiment, testis sizes of ‘photo+food-stimulated’ birds, but not ‘control’ birds, also increased. We suggest that the capability to respond to both food and photoperiodic cues allows animal the flexibility to adjust reproductive activity to variable environmental conditions each year. Future work should elucidate whether food provides nutritional or non-nutritional cues, and the neurophysiological mechanisms by which food stimulates reproductive activity.     

Genetic diversity and population structure in Tunisian Lavandula stoechas L. and Lavandula multifida L. (Lamiaceae)

The genetic diversity and population structure of 20 Tunisian Lavandula stoechas L. and Lavandula multifida L. populations, from different bioclimates, were analysed by starch gel electrophoresis using seven isozymes. The genetic diversity within populations varied according to species. Variation in L. multifida was higher than that observed for L. stoechas, and exclusive alleles were detected for taxa.

A high differentiation among populations, for each species, estimated by Wright's F-statistics was revealed. The genetic structure of populations from the same bioclimate was substantial. Nei's, R. [1978. Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89, 583–590] genetic distance among pairs of populations was low. The UPGMA cluster analysis of genetic distance values revealed that populations for each species were not strictly clustered together according to bioclimate or geographic proximity.

For each species, the low genetic divergence among populations and their substantial structure indicate their recent fragmentation due to anthropic pressures. The dendrogram generated from pairwise genetic distance among all populations showed two distinct clusters each corresponding to one species. The high genetic divergence between the two species, based on isozymes, corroborates their taxonomic status, as previously reported using morphological traits. The strategy for the management and conservation of populations should be made for each taxa according to its level of diversity and bioclimate.