Search

Abstract: Arceuthobium americanum Nutt. ex Engelm., the lodgepole pine dwarf mistletoe, is a dioecious parasitic flowering plant infecting lodgepole pine (Pinus contorta subsp. latifolia (Engelm.) Critchfield) in the Pacific Northwest, [...]

Abstract: Dwarf mistletoes (DM), genus Arceuthobium, are dioecious parasitic flowering plants having prolonged life cycles lasting six years, culminating with explosive discharge of the single seed from the fruit. Arceuthobium [...]

Abstract: Arceuthobium americanum Nutt. ex Engelm. (lodgepole pine dwarf mistletoe) is a dioecious plant parasitizing conifers in North America. Here, we documented changes in the 'taxonomic richness' of culturable endophytic [...]

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a parasitic angiosperm that infects conifers in western Canadian forests. While production of viable pollen in anthers is critical to dwarf mistletoe reproduction, the few existing reports that examine staminate development in Arceuthobium are often incomplete or conflicting. The objective of this work was to investigate the developmental anatomy of anther and pollen of A. americanum using modern microscopy. We found that the microsporangium was toroidal from the outset and gave rise to a central peg-shaped sterile 'columella' early in anther development. The endothecium was absent, the epidermis persisted as an 'exothecium' fulfilling the role of the endothecium, and a primary parietal layer generated a secretory tapetum and middle layer. Thus, we suggest that a new category of anther wall development, the Arceuthobium type, be created. Microsporogenesis produced tetrahedral microspores via simultaneous cytokinesis and involved callose wall formation. Microgametogenesis resulted in round and atypical generative and vegetative nuclei. Additionally, the heterocolpate, echinate pollen grains, which were shed at the two-celled stage, were seen for the first time in their native state with environmental scanning electron microscopy. This work contributes to the understanding of A. americanum, the genus Arceuthobium, and angiosperms as a whole. Key words: anatomy, cytochemistry, dwarf mistletoe, microscopy, microsporogenesis, microgametogenesis. Le gui nain du pin lodgepole, Arceuthobium americanum Nutt. ex Engelm., est une angiosperme parasite qui infecte les coniferes des forets de l'Ouest du Canada. Alors que la production de pollen viable par les antheres est critique a la reproduction du gui nain, les rapports actuels, peu nombreux, qui se sont penches sur le developpement stamine chez Arceuthobium sont souvent incomplets ou contradictoires. L'objectif de ce travail etait d'examiner l'anatomie developpementale des antheres et du pollen d'A. americanum par microscopie moderne. Nous avons trouve que le microsporange etait en forme d'anneau des le debut et donnait naissance a une << columelle >> centrale conoide sterile tot lors du developpement de l'anthere. L'endotheque etait absente, l'epiderme persistait comme << exotheque >>, remplissant le role de l'endotheque, et une couche parietale primaire generaitun tapetum secretaire etune couche intermediaire; ainsi, nous suggerons qu'une nouvelle modalite de developpement de la paroi de l'anthere soit creee, le type <>. La microsporogenese produisait des microspores tetraedriques par cytocinese simultanee, et elle impliquait la formation d'une paroi calleuse. La microgametogenese resultait en noyaux generatifs et vegetatifs ronds et atypiques. De plus, les grains de pollen heterocolpes echines qui etaient liberes au stade biloculaire ont ete observes pour la premiere fois dans leur etat natif par microscopie electronique a balayage environnemental. Ce travail contribue a mieux comprendre globalement A. americanum, le genre Arceuthobium, et les angiospermes. Mots-cles: anatomie, cytochimie, gui nain, microscopie, microsporogenese, microgametogenese., Introduction Dwarf mistletoes (genus Arceuthobium, Santalaceae) are obligate aerial parasites found on members of Pinaceae and Cupressaceae (Hawksworth and Wiens 1996). These dioecious parasites compromise the health of the host [...]

The floral nectaries of three Tillandsia L. spp. having different pollinators were investigated with transmission electron microscopy (TEM) to describe the previously unstudied ultrastructure of the nectar-producing tissues (primarily the epidermis) and also to determine if any differences in the ultrastructural features could be correlated to pollination mode. We determined that there were variations in nectaries among the three species, and that these may be linked to pollinator choice. Tillandsia seleriana Mez, which has a strict relationship with ants, had a nectary epithelium characterized by abundant dictyosomes and endoplasmic reticulum (ER), and a final degeneration stage possibly leading to holocrine secretion. The presence of protein crystals in epithelial plastids was correlated to a nectar enriched with amino acids and proteins, likely functioning to provide a protein-enriched diet and possibly defence against pathogens. Epithelial cells of the hummingbird-pollinated Tillandsia juncea (Ruiz et Pav.) Poir. nectary displayed cell wall ingrowths and dictyosomes and also contained cytoplasmic lipid droplets and protein crystals within plastids, both of which would enrich the nectar for hummingbirds. The nectary epithelium and the parenchyma of bat-pollinated Tillandsia grandis Schltdl. possessed a few cubic protein crystals in the plastids and its secretion product appeared electron transparent. Key words: electron microscopy, nectar(y), pollination, secretion, Tillandsia. A l'aide de la microscopie electronique par transmission (MET), les auteurs ont examine les nectaires floraux chez trois especes de Tillandsia L, accueillant differents pollinisateurs. Les objectifs consistaient a decrire les ultrastructures jamais etudiees des tissus producteurs du nectar (surtout l'epiderme) et a determiner s'il existe des differences dans les caracteristiques ultrastructurales correspondant au mode de pollinisation. Ils ont observe une variation des nectaires selon chacune des trois especes. Chez le Tillandsia seleriana Mez, elles peuvent etre reliees au choix des pollinisateurs, ayant une relation stricte avec les fourmis; dans ce cas, l'epithelium des nectaires se caracterise par d'abondants dictyosomes et reticulum endoplasmique (RE), ainsi que par un stade de degeneration finale conduisant possiblement a une secretion holocrine. On observe une correlation entre la presence de proteines cristallisees dans les plastes epitheliaux avec un enrichissement du nectar en acides amines et proteines, fournissant probablement une diete enrichie en proteines et possiblement une defense contre les pathogenes. Les cellules epitheliales des nectaires du Tillandsia juncea (Ruiz et Pav.) Poir. montrent des invaginations cellulaires et des dictyosomes et contiennent egalement des gouttelettes lipidiques cytoplasmiques ainsi que des proteines cristallisees dans les plastes; ces deux apports pourraient enrichir le nectar recherche par les oiseaux-mouches. L'epithelium des nectaires et meme le parenchyme du Tillandsia grandis Schltdl., pollinise par des chauves-souris, possedent quelques cristaux cubiques de proteines dans les plastes, ce produit de secretion etant transparent aux electrons. [Traduit par la Redaction] Mots-cles: microscopie electronique, nectaire, nectar, pollinisation, secretion, Tillandsia., Introduction Pollination is an essential process in angiosperm reproduction. Animals--typically insects, birds, and bats--are often integral to pollination. The production of carbohydrate-based solutions (nectar) in specialized tissues (nectaries) is a [...]

In this study, we proposed that a constant gradient magnetic field could be generated by the construction of a current-carrying coil possessing a turn-density (number of turns per unit length) that varies linearly with axial position (i.e., a varying turn-density coil, VTDC). A VTDC is easily constructed and could be used to demonstrate how a ferromagnet placed in a magnetic field experiences a net force. Using the Biot-Savart law, we predicted that a ferromagnetic dipole suspended in a VTDC experiences a force proportional to the length of the dipole. We designed and executed an experiment to test our prediction. A coil with a turn-density varying at a rate of 0.11 [cm.sup.-2] was constructed. Rare-earth magnets were suspended along the centre of the VTDC using a string that was attached to a mass resting on a scale. The scale reading measured the force experienced by the hanging magnet. The procedures were also carried out in a constant turn-density solenoid (control). A direct linear relationship between force and magnet length was observed in the VTDC, whereas no force was detected in the zero-gradient field solenoid (p < 0.000 001). Linear regressions suggested that the observed data matched the predicted values (95% certainty). The magnetic moment of 0.56 ± 0.21 J/T is in reasonable agreement with remnant magnetization for neodymium magnets of ~1 T. We found that our easily-built VTDC produced a uniform gradient as no significant differences were observed when magnets were hung at different axial positions. Overall, the results were supportive of the theory. Our VTDC could be readily constructed and used in a physics classroom to demonstrate basic principles of electromagnetism. PACS Nos.: 01.50.My, 41.20.Gz. Dans cette etude, nous avancons qu'un gradient constant de champ magnetique peut etre genere en construisant un solenoide portant un courant avec une densite de tours (nombre de tours par unite de longueur) qui varie lineairement avec la position axiale (un solenoide a densite de tour variable ou VTDC). Un VTDC est facile a construire et peut etre utilise pour demontrer comment un echantillon ferromagnetique place dans un champ magnetique ressent une force nette. Utilisant la loi de Biot-Savard nous predisons qu'un dipole ferromagnetique suspendu dans un VTDC ressent une force proportionnelle a la longueur du dipole. Nous avons developpe et complete une experience pour prouver notre prediction. Nous avons construit un solenoide avec une densite de tour variable au taux de 0.11 [cm.sup.-2]. Nous avons a tour de role suspendu des aimants faits de terre rare le long du centre de la bobine, chacun retenu par un fil attache a une masse au repos sur une balance. La masure de la balance donne la force ressentie par l'aimant suspendu. Nous avons repete la procedure avec une bobine a densite de tour constante pour fin de controle. Nous avons observe une relation lineaire entre la force et la longueur de l'aimant dans le VTDC, alors qu'aucune force n'a ete detectee dans le solenoide a gradient nul de champ (p < 0.000 001). La regression lineaire suggere que les donnees observees agreent avec les valeurs predites (95%). Le moment magnetique de 0.56 ± 0.21 J/T agree raisonnablement avec la magnetisation remanente pour un aimant de neodyme de ~1 T. Nous trouvons que nos VTDC faciles a construire produisent un gradient uniforme, puisqu'aucune difference n'est observee pour des aimants suspendus a differentes positions axiales. Dans l'ensemble, les resultats supportent notre theorie. Notre VTDC pourrait etre facilement construit et utilise dans des classes de physique pour demontrer des principes de base de l'electromagnetisme. [Traduit par la Redaction], 1. Introduction The magnetic force [1] is a requisite topic of study for students studying physics in both high school and college or university. Introductory texts on the magnetic force [...]

In North America, the most widespread and speciose mistletoe is Arceuthobium M. Bieb. (dwarf mistletoes, Viscaceae), which is a dioecious parasite of conifers. Little is known about its sex determination system, and sex chromosomes have not been identified. A genetic marker for early gender discrimination in Arceuthobium would be useful in the study of sex ratios and sex determination. Here, random amplified polymorphic DNA analysis via the polymerase chain reaction (PCR) was used to investigate genetic differences between genders in Arceuthobium americanum Nutt. ex Engelm. collected near Kamloops, British Columbia, and Belair, Manitoba. A total of 196 10-mer primers were selected for analysis of DNA from isolated male and female A. americanum somatic tissue. A ~900 bp female-specific DNA fragment was generated with primer OPB-18 (5'-CCACAGCAGT-3'). The fragment was cloned and sequenced. Using GenBank and the basic local alignment search tool alignment software, it was determined that the first ~300 bp of this DNA sequence shared a high degree of similarity to transposable elements (76%) and a Y-chromosome (male) fragment (75%) in Silene latifolia Poir. Sequence-characterized amplified region primers were then designed. This study has generated an efficient molecular tool to differentiate male and female A. americanum while also providing evidence indicating that A. americanum may have homomorphic, possibly protoheteromorphic, sex chromosomes. Key words: dwarf mistletoes, gender discrimination, polymerase chain reaction, primers, random amplified polymorphic DNA, sequence characterized amplified regions. En Amerique du Nord, le genre Arceuthobium (gui nain, Viscaceae), parasites dioi'ques sur les coniferes, est le plus repandu et le plus riche en especes. On connait peu de chose sur le systeme de determination du sexe et l'on n'a pas encore identifie les chromosomes porteurs du sexe. Il serait utile de disposer d'un marqueur permettant de determiner hativement le genre chez les Arceuthobium dans les etudes sur les ratios des sexes et la determination des sexes. Les auteurs ont utilise l'analyse du polymorphisme de l'ADN amplifie aleatoirement (RAPD) en utilisant la reaction par polymerisation en chaine (PCR) pour examiner les differences genetiques entre les genres chez l'Arceuthobium americanum Nutt. ex Engelm. recolte pres de Kamloops, en Colombie Canadienne et a Belair au Manitoba. Ils ont selectionne un total de 196 amorces << 10-meres >> pour analyser l'ADN isole de tissus somatiques de plants males et femelles de l'A. americanum, a l'aide de l'amorce OPB-18 (5'-CCACAGCAGT-3'). Ils ont clone et sequence le fragment. En utilisant comme outil le logiciel de recherche basique d'alignement local (BLAST), on a determine que les 300 premieres pb de cette sequence ADN partagent un fort degre de similitude avec des elements transposables (76%) et un fragment (75%) du chromosome Y (male) du Silene latifolia. Les auteurs ont ensuite construit des amorces provenant d'une sequence amplifiee d'une region caracterisee (SCAR). Cette etude a genere un outil moleculaire efficace pour differencier les plantes males et femelles de l'A. americanum tout en fournissant une preuve que l'A. americanum pourrait posseder des chromosomes sexuels homomorphes, possiblement protoheteromorphes. Mots-cles : gui nain, discrimination des genres, reaction en chaine par polymerase, polymorphisme de l'ADN amplifie aleatoirement, sequence amplifiee de regions caracterisees., [Traduit par la Redaction] Introduction The genus Arceuthobium M. Bieb. (Viscaceae), also known as dwarf mistletoes, comprises a group of obligate aerial parasites on Pinaceae and Cupressaceae. Arceuthobium americanum Nutt. [...]

The human Y chromosome began to evolve from an autosome hundreds of millions of years ago, acquiring a sex-determining function and undergoing a series of inversions that suppressed crossing over with the X chromosome (1,2). Little is known about the recent evolution of the Y chromosome because only the human Y chromosome has been fully sequenced. Prevailing theories hold that Y chromosomes evolve by gene loss, the pace of which slows over time, eventually leading to a paucity of genes, and stasis (3,4). These theories have been buttressed by partial sequence data from newly emergent plant and animal Y chromosomes (5-8), but they have not been tested in older, highly evolved Y chromosomes such as that of humans. Here we finished sequencing of the male-specific region of the Y chromosome (MSY) in our closest living relative, the chimpanzee, achieving levels of accuracy and completion previously reached for the human MSY. By comparing the MSYs of the two species we show that they differ radically in sequence structure and gene content, indicating rapid evolution during the past 6 million years. The chimpanzee MSY contains twice as many massive palindromes as the human MSY, yet it has lost large fractions of the MSY protein-coding genes and gene families present in the last common ancestor. We suggest that the extraordinary divergence of the chimpanzee and human MSYs was driven by four synergistic factors: the prominent role of the MSY in sperm production, 'genetic hitchhiking' effects in the absence of meiotic crossing over, frequent ectopic recombination within the MSY, and species differences in mating behaviour. Although genetic decay may be the principal dynamic in the evolution of newly emergent Y chromosomes, wholesale renovation is the paramount theme in the continuing evolution of chimpanzee, human and perhaps other older MSYs., This study required that we first complete the sequencing of the chimpanzee MSY (9-11) using large-insert bacterial artificial chromosome (BAC) clones and the iterative mapping and sequencing strategy used to [...]

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a parasitic angiosperm that infects conifers in western Canadian forests. A striking feature of the Arceuthobium life cycle is explosive seed dispersal, triggered by hydrostatic build-up within the fruit, localized in a tissue called 'viscin.' Viscin is composed of two cell types: 'viscin cells' that accrue pressure in their hydrated mucilage, and 'vesicular cells' with a previously undetermined function. The objective of this work was to investigate the development and composition of vesicular cells using microscopy, cytochemistry, and gas chromatography--mass spectroscopy. We found that vesicular cells are initiated from mesocarp cells lining the viscin cells. As development of the seed progresses, vesicular cells form a single layer, enlarge, and become isodiametric. Later, the cells make up all of the remaining 3-4 outer mesocarp layers. Concomitant with enlargement, intracellular triacylglycerides (TAGs) largely composed of 16-carbon and 18-carbon fatty acids, accumulate. Immediately prior to discharge, vesicular cell boundaries become indistinct, and the cell contents become confluent, creating a lipid mass between the viscin cells and the exocarp. Vesicular cells and their resulting lipid mass likely function in discharge by acting as a hydrophobic barrier to water loss and (or) as a repellant, resistant layer. Key words: cytochemistry, dwarf mistletoe, gas chromatography--mass spectroscopy (GC-MS), triacylglycerides (TAGs), viscin tissue. Le gui nain du pin lodgepole, Arceuthobium americanum, est une angiosperme parasite infectant les forets de l'Ouest canadien. On y observe une caracteristique bien particuliere, soit la dispersion explosive des graines, declenchee par la formation d'une pression hydrostatique a l'interieur du fruit, localizee dans un tissu 'vicinal.' Ce tissu comporte deux types de cellules: les 'cellules vicinales' qui augmentent la pression dans leur mucilage hydrate et les 'cellules vesiculaires', dont la fonction n'a encore jamais ete definie. Les auteurs ont etudie le developpement et la composition des cellules vesiculaires a 'aide de la microscopie, de la cytochimie et de la chromatographie en phase gazeuse--spectroscopie de masse. Its ont constate que les cellules vesiculaires prennent naissance dans les cellules du mesocarpe bordant les cellules vicinales. An cours du developpement de la graine, les cellules vesiculaires forment une seule couche, grossissent et deviennent isodiametriques. Plus tard, les cellules transforment toutes les cellules residuelles des 3-4 couches du mesocarpe exteme. De fargon concomitante avec l'agrandissement, elles accumulent des triacylglycerides (TAGs) constitues surtout d'acides gras a 16 et 18 carbones. Immediatement avant la decharge, le pourtour des cellules vesiculaires devient indistinct, et les contenus des cellules deviennent confluents, creant une masse lipidique entre les cellules vicinales et l'exocarpe. Les cellules vesiculaires et la masse lipidique qui en resulte interviennent vraisemblablement dans la dicharge, en agissant comme couche de resistance sous forme d'une barriere hydrophobe a la perte de 'eau on comme repulsif. Mots-cles: cytochimie, gui nain, chromatographie en phase gazeuse--spectrographie de masse (GC-MS), triacylglycerides (TAGs), tissu vicinal. [Traduit par la Redaction], Introduction Mistletoes are flowering plants and aerial parasites belonging to the order Satantalales (Kuijt 1968; Cronquist 1981; Mathiasen et al. 2008). The mistletoe habit is believed to have evolved five [...]

Abstract: The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a dioecious angiosperm that parasitizes conifers in western Canadian forests, causing significant yearly timber loss. A striking consequence [...]

Ovarian carcinomas with mutations in the tumour suppressor BRCA2 are particularly sensitive to platinum compounds (1). However, such carcinomas ultimately develop cisplatin resistance. The mechanism of that resistance is largely [...]

Author(s): Michael C. Zody (corresponding author) [1]; Manuel Garber [1]; Ted Sharpe [1]; Sarah K. Young [1]; Lee Rowen [2]; Keith O'Neill [1]; Charles A. Whittaker [1, 6]; Michael Kamal [...]

Author(s): Elena V. Linardopoulou [1, 2]; Eleanor M. Williams [1]; Yuxin Fan [1, 4]; Cynthia Friedman [1]; Janet M. Young [1]; Barbara J. Trask (corresponding author) [1, 2, 3] The [...]

Author(s): The International Human Genome Mapping Consortium ; Washington University School of Medicine, Genome Sequencing Center: ; John D. McPherson (corresponding author) [1]; Marco Marra [1]; LaDeana Hillier [1]; Robert [...]