Ultrastructure of spermatogenesis in Cerastoderma glaucum (Cardiacea) and Spisula subtruncata (Mactracea)

Summary

In Cerastoderma glaucum, Sertoli cells are rich in lipids, glycogen and lysosomes, and premeiotic cells exhibited nuage, a prominent Golgi complex and endoplasmic reticulum cisternae encircling the nucleus. The Golgi complex gives rise to proacrosomal vesicles during mid-spermiogenesis, and the round acrosomal vesicle, with a dense fibrillar core, migrates laterally while linked to the plasma membrane as it develops the subacrosomal material. In its final position, the vesicle becomes cap-shaped (0.6 μm) and differentiates into apical light and basal dense regions. The elongated and helicoidal nucleus (8–9.9 μm) has a thin tip (0.3 μm) that invades the subacrosomal space, and in the midpiece (0.8 μm) two of the four mitochondria extend laterally to the nucleus (1.5–2.1 μm). In Spisula subtruncata, Sertoli cells are rich in lipids, glycogen and phagocytosed sperm. Premeiotic cells exhibit nuage, a prominent Golgi complex that gives rise to proacrosomal vesicles from the leptotene stage and a flagellimi that is extruded at zygotene. The acrosomal vesicle forms during the round spermatid stage and differentiates into a large and dense basal region and an apical light region. It then migrates while linked to the plasma membrane by its apical pole. Development of the subacrosomal perforatorium is associated with nuage materials and endoplasmic reticulum vesicles. The mature cap-shaped (0.6 μm) acrosomal vesicle exhibits a large apical and irregular region with floccular contents and a basal dense region. The round nucleus becomes barrel-shaped (1.5 μm) and the midpiece (0.8 μm), with four mitochondria, contains a few glycogen particles.     

Cloning and characterization of cDNA probes for the analysis of metallothionein gene expression in the Mediterranean bivalves: <Emphasis Type="Italic">Ruditapes decussatus</Emphasis> and <Emphasis Type="Italic">Cerastoderma glaucum</Emphasis>

cDNA probes have been developed for subsequent use in monitoring the cadmium exposure of the clam Ruditapes decussatus and the cockle Cerastoderma glaucum using metallothionein (MT) gene expression in different tissues of these species. Two partial MT cDNAs were isolated from Ruditapes decussatus and Cerastoderma glaucum. The identification of the nucleotide sequences showed that the cDNAs consist of 480 bp coding 72 amino acid proteins containing 21 cysteine residues organized in Cys–X–Cys motifs as classically described for MTs. The induction of MT gene expression in CdCl₂ treated bivalves was confirmed by dot blot analysis and suggests a potential specific tissue expression rate.     

Isozymic classification of pearl millet (Pennisetum glaucum,Poaceae) landraces from Niger (West Africa)

The principal landraces of the pearl millet,Pennisetum glaucum (L.)R. Br., from Niger have been analysed for their genetic structure at eight enzyme systems coded by 12 loci and 46 alleles. Three groups have been identified: (1) early-maturing pearl millets, cultivated between 8° and 13°E longitude, including the oases from Aïr mountains; (2) early-maturing millets situated more to the west (1° and 8°E longitude), and (3) late-maturing millets. Group 1 shows the highest isozyme diversity. The differences between the accessions represent 8.8% of the total diversity and the differences between the three groups 4.5%. The accessions from groups 1 and 3 are the least distant. When considering pearl millets from areas outside Niger, the chadian and sudanese millets are enzymatically close to the Niger group 1. The pearl millets from Niger group 2 are close to millets from east Mali, northern Burkina Faso and Senegal, and the Niger group 3 to the late-maturing millets group from West Africa. This study should help breeders to select the landraces for improvement and parents for crosses from cultivars of Niger and introduced germ plasm.     

The karyotype of Nodipecten nodosus (Bivalvia: Pectinidae)

Earlier karyotypical work on Nodipecten nodosus embryos indicated that this species has a diploid number of 38, with six pairs respectively of metacentric and submetacentric chromosomes and seven pairs of subtelocentric chromosomes, although there were some difficulties in obtaining complete metaphases. The present work provides additional results on specific regions of the chromosomes in N. nodosus and, by meiotic studies, confirms the chromosome number with more reliability. Active nucleolar organizer regions (NOR), detected in mitotic metaphases from embryos, can be characterized in N. nodosus by a high level of heteromorphism of NOR-sites, indicating that these regions are not appropriate as chromosomal markers in this species. The procedure for detecting constitutive heterochromatin of chromosomes allowed us to observe most of the heterochromatic blocks at a pericentromeric position and some at telomeric and interstitial positions. The analysis of meiotic chromosomes from gonad tissue revealed the presence of 19 bivalents during metaphase I, all homomorphic and isopicnotic, confirming the previously described diploid chromosomal number of 38 for N. nodosus. From these results, some evolutionary aspects of the Pectinidae are briefly discussed.     

Copepoda Poecilostomatoida associated with Bivalvia from New Guinea

Four species of Copepoda Poecilostomatoida are recorded from the mantle cavity of bivalve molluscs collected in West New Guinea (Irian Barat, Indonesia). Two of these are new to science: Pseudanthessius dimorphus and Lichomolgus hoi n. spp.     

葱属Anguinum亚属4种19居群的核型研究

石蒜科(Amaryllidaceae)葱亚科(Allioideae)葱族(Allieae)葱属(Allium)的Anguinum亚属在中国分布有6种2变种,该亚属植物具有重要的药用价值。该研究在扩大样本量和覆盖范围的基础上,采用常规压片法对葱属Anguinum亚属4种植物19居群的染色体核型进行了研究,首次报道了心叶韭(Allium ovalifolium var.cordifolium)的核型。结果表明:供试类群中茖葱都为四倍体,对叶韭和心叶韭都为二倍体,太白韭具有二倍体和四倍体,染色体基数均为x=8,核型类型都为2A型,每个居群都具有随体染色体,随体染色体多为st染色体,随体均位于短臂末端,并且对叶韭眉县居群和太白韭聂拉木居群存在B染色体。结合前人研究结果讨论了Anguinum亚属植物的染色体特征、随体染色体的多态性和该亚属植物的进化方式,探讨了茖葱(Allium victorialis)和对叶韭(A.listera)的细胞地理学问题。得到如下推论:(1)染色体加倍和结构变异是Anguinum亚属进化的两种重要机制,环境异质性使得Anguinum亚属植物随体染色体具较高的多态性;(2)茖葱通过多倍化和无性繁殖并存来扩大居群;(3)染色体形态变异是对叶韭适应环境变异的重要方式。     

Two Corbicula (Corbiculidae: Bivalvia) mitochondrial lineages are widely distributed in Asian freshwater environment

We investigated the biogeography of Asian Corbicula using mitochondrial gene sequence variation for Corbicula members sampled from 24 localities of eight Asian regions. A total of 210 individuals were genetically characterized by examining sequence variations of a 614 bp fragment of the mitochondrial cytochrome oxidase I (COI) gene. Phylogenetic analyses of the COI dataset revealed that Corbicula members are subdivided into two well-supported clades: estuarine and freshwater. A robust dichotomy between the Japanese/Korean (Corbicula japonica) and Chinese (Corbicula fluminalis) estuarine forms was evident, suggesting that these two regional populations represent a deep phylogeographic split. Our mitochondrial gene tree showed that among the freshwater members, two Corbicula mitochondrial lineages are the most common, having attained extensive geographic distribution in the Asian freshwater environment. While the present study provides significant biogeographic information on Asian Corbicula, a comprehensive phylogenetic study by cross-referencing the mitochondrial-based Corbicula phylogeny with nuclear gene data is required to fully understand the evolutionary origin(s) of triploidy/clonality in this genus.     

The expression and perpetuation of inherent somatic variation in regenerants from embryogenic cultures of Pennisetum glaucum (L.) R. Br. (pearl millet)

Summary Genetic analysis was conducted on the qualitative and quantitative traits of sexual progeny derived from embryogenic cultures of two inbred lines of Pennisetum glaucum (L.) R. Br. (pearl millet). These lines included a genetically stable inbred of Tift 23 BE and a genetic marker line, derived from Tift 23BE, which bore qualitative genetic markers for a dominant purple plant trait (P) and two recessive traits, early flowering (e₁) and yellow stripe (ys). Tissue culture regenerant populations (R₀) and progeny populations (R₁) produced from these plants by selfing showed no qualitative genetic variation when derived from the genetically stable inbred Tift 23BE. In contrast, stably inherited qualitative variation for a number of genetic markers was observed in R₀, R₁, and R₂ progeny of the genetic marker line. In a population of 1,911 plants regenerated over a 12-month period, 0.02% of the population lost or showed reduced expression of the purple plant trait and 92% of plants were chlorophyll deficient. Plants showing reduction or loss of anthocyanin synthesis also flowered later. None of the purple plants showed any significant variation in flowering time. The incidence of chlorophyll deficiency increased with time in culture, 51 % of the progeny regenerated after 1 month were chlorophyll deficient, while 100% of the plants regnerated after 12 months were chlorophyll deficient. Qualitative variation was also observed in control populations of the genetic marker line where 1 plant in a total of 1,010 lacked purple pigmentation and a total of 6% showed chlorophyll variation in the first generation (S₀). The presence of qualitative variation in controls suggests that the inherent variation present in the original explant was expressed and perpetuated in vitro. Quantitative variation was observed for a number of traits in the first sexual cycle (R₁) of the marker line but did not occur in a subsequent generation, suggesting that this variation was epigenetic.     

Analysis of recombination rate in female and male gametogenesis in pearl millet (Pennisetum glaucum) using RFLP markers

Sex as a factor affecting recovered recombination in plant gametes was investigated in pearl millet, Pennisetum glaucum, by using reciprocal three-way crosses [(AxB)xCvCx(A x B)]. The two populations were mapped at 42 loci pre-selected to cover the majority of the genome. No differences in recombination distances were observed at the whole-genome level and only a few individual linkage intervals were found to differ, all in favour of increased recombination through the male. Distorted segregations found in the three-way crosses provide evidence of post-gametic selection for particular gene(s) or chromosome regions. The significance of these results for the design of pearl millet breeding programmes and inheritance experiments, as well as for other experimental strategies, is discussed.     

Ring formation and annual growth in Corbicula consobrina Caillaud, 1827 (Bivalvia,Corbiculidae)

The growth of C. consobrina of the White Nile near Khartoum was studied during March–December, 1977 from material collected from fish guts every two months. It was found that the growth season extends from February to July in correlation with the rise in temperature. Food was abundant and the concentration of the dissolved calcium in the river water was also increasing.During the flood season from July to October, the clams entered a resting state as a result of the annual siltation and consequently growth was arrested. Growth rings were found to be formed as a result of the siltation-induced resting state.There is evidence that little growth occurred during the cooler months from October to December. The development of the false rings on the shells is possibly a result of the changes in the water levels.Analysis of the growth of the adult clams showed that there is a clear size-time relation; there was close agreement between the calculated maximum sizes and the actual data collected from the field.Other examples from Sudanese inland waters were also discussed. The role of the annual hydrological cycles in regulating the populations activities and hence the growth of the individuals was found to be important.     

新建迭部蛤(新名) (Tewomorpha)替代晚出名)(Tewoella Ding and Li, 1987 (非)(Tewoella Sun, 1979)

1993年, 于菁珊和董国义为辽宁上三叠统的非海相双壳类化石建立了一个新属辽宁蚌Liaoningia Yu and Dong, 1993, 以Liaoningia opima Yu and Dong, 1993作为模式种。然而, 早在1979年, 邢裕盛和刘桂芝就已为辽宁晚前寒武纪南关岭组所产的化石标本创建了新属名辽宁水母属Liaoningia Xing and Liu, 1979, 模式种是Liaoningia fuxianensis Xing and Liu, 1979。然而, 多数学者反对将它视为水母类化石, 有人怀疑辽宁水母属是假化石, 迄今学术界并无统一意见, 故本文暂将它归为疑问化石(Problematica)。根据“国际动物命名法规”, 我们提出一个新的属名Liaoningoconcha nom. nov., 用以替代Liaoningia Xing and Liu, 1979的次同义名Liaoningia Yu and Dong, 1993, 仍使用于菁珊和董国义在1993年指定的模式种, 中文译名不变。     

Genetic insight into Mediterranean chukar (Alectoris chukar, Galliformes) populations inferred from mitochondrial DNA and RAPD markers

The chukar (Alectoris chukar, Galliformes) is one of the most important game birds as it is widely distributed and hunted over the whole of its range. The aim of this work was to assess the genetic differentiation as well as the possible presence of hybrid specimens in A. chukar populations from Italy, Greece and Cyprus. To provide phylogenetic context, conspecific, allopatric specimens from Israel, Georgia, Armenia, Kazakhstan, Afghanistan, Pakistan, Mongolia, China and USA were compared. Sequencing of the mitochondrial DNA (mtDNA) Control Region supplied information on the ancestry of A. chukar populations, whereas Random Amplified Polymorphic DNA (RAPD) fingerprinting was used to assess whether hybridization had occurred. The Italian population was found to be an inter-specific mixture of A. chukar and A. rufa (i.e., the red-legged partridge) mtDNA lineages, whereas the representatives from Greece and Cyprus showed only the A. chukar maternal line. RAPD markers revealed introgression with A. rufa genes in the Italian population, whereas no A. chukar × A. rufa hybrid specimens were detected in the eastern Mediterranean populations. The genetic data obtained from the Italian A. chukar population as well as from a few Greek specimens pointed against their Mediterranean kinship, suggesting relationships with A. chukar subspecies from the easternmost part of the Asian continent.     

Reproduction and sperm structure in Galeommatidae (Bivalvia, Galeommatoidea)

Reproduction and/or sperm structure was studied in 18 species belonging to five genera of Galeommatidae from Phuket Island, Andaman Sea, Thailand, and Hong Kong. Incubation of the ova occurs in the inner and outer demibranchs of both gills, and sperm is most probably transferred to the ctenidial brood chamber as masses of agglutinated and non-encapsulated spermatozoa. The smallest specimens are males, but change into the female sex and there is a strong indication that some of the species are alternate hermaphrodites. Dwarf males occur in one species (Galeomma layardi). The sperm of all 18 species studied are of the ent-aquasperm type with a more or less hemispherical acrosome that is tilted with respect to the long axis of the moderately elongated nucleus. It is suggested that this type of sperm affords the best autapomorphy for the family Galeommatidae.     

Karyotypes,C-banding and nucleolar numbers inGuizotia (Compositae)

Karyotypes, constitutive heterochromatin and nucleolar numbers of five recognized taxa and two systematically new populations ofGuizotia have been studied using Giemsa or aceto-orcein staining, C-banding and silver nitrate staining. All accessions have 2n = 30 chromosomes, but satellite chromosome number and nucleolar number varied from four to eight. Centromere positions varied from predominantly median to submedian and subterminal in different materials. The satellites and an interstitial region in the short arm of one chromosome pair were C-banded in all materials. Telomeric and centromeric C-bands were also observed. The material could be classified into three groups, indicating possible phylogenetic relationships.     

云南泸定百合8个野生居群的染色体核型分析

用常规压片法,对云南省境内泸定百合(Lilium sargentiae Wilson)8个野生居群的染色体进行了核型分析,结果显示:(1)野生泸定百合8个居群均为二倍体(2n=2x=24),染色体基数为12,共24条染色体,无B染色体;(2)核型类型均为3A,第1、2对染色体均为具中部(m)或近中部(sm)着丝点的大形染色体,且第1对染色体上均具有随体;(3)染色体长度比为1.64～2.26,平均臂比为6.43～8.22,核型不对称系数为79.82% ～ 81.77%。研究表明,泸定百合染色体数相对稳定,染色体变异主要表现在结构变异,各个居群的染色体组成、随体数、随体位置、臂比、染色体长度比及核型不对称系数均有差异,泸定百合各居群间存在明显的核型多态性。