A cellular growth model for root tips

Growth of the root tip is modeled using a one-dimensional string of cells. Each cell is characterized by three distinct phases, division, elongation-only or maturity. In this model two hypothetical phytohormones, one produced at the root tip and the other at the shoot, determine the behavior of the cell, and therefore the growth of the entire tip. While the division rate is taken to be a step function of the string coordinate, the growth rate of each cell is assumed to be piecewise linear and composed of linear functions of cell length. Thereafter, suitable operators for the calculation of the velocity and relative growth rate distributions are given. The results of the model are finally compared to measurements of Arabidopsis thaliana, Nicotiana tabacum and Pisum sativum roots.     

Polychaete chaetae: Function, fossils, and phylogeny

In this article we review the phylogenetic distribution of majorchaetal types within the Polychaeta, discuss what has been demonstratedabout chaetal function in modern worms, and examine what isknown about the evolution of chaete through the fossil record.We conclude with specific cautions about how chaetae are treatedin phylogenetic analyses and make suggestions about how theycould be used to provide a stronger phylogenetic signal.     

Perfect phylogeny haplotyper: haplotype inferral using a tree model

SUMMARY: We have developed an efficient program, the Perfect Phylogeny Haplotyper (PPH) that takes in unphased population genotype data, and determines if that data can be explained by haplotype pairs that could have evolved on a perfect phylogeny.     

Integrating Early Cretaceous fossils into the phylogeny of living angiosperms:Magnoliidae and eudicots

Over the past 25 years, discoveries of Early Cretaceous fossil flowers, often associated with pollen and sometimes with vegetative parts, have revolutionized our understanding of the morphology and diversity of early angiosperms. However, few of these fossils have been integrated into the increasingly robust phylogeny of living angiosperms based primarily on molecular data. To remedy this situation, we have used a morphological dataset for living basal angiosperms (including basal eudicots and monocots) to assess the most parsimonious positions of early angiosperm fossils on cladograms of Recent plants, using constraint trees that represent the current range of hypotheses on higher-level relationships, and concentrating on Magnoliidae (the clade including Magnoliales, Laurales, Canellales, and Piperales) and eudicots. In magnoliids, our results confirm proposed relationships of Archaeanthus (latest Albian?) to Magnoliaceae, Endressinia (late Aptian) to Magnoliales (the clade comprising Degeneria, Galbulimima, Eupomatia, and Annonaceae), and Walkeripollis pollen tetrads (late Barremian?) to Win-teraceae, but they indicate that Mauldinia (early Cenomanian) was sister to both Lauraceae and Hernandiaceae rather than to Lauraceae alone. Among middle Albian to early Cenomanian eudicots, we confirm relationships of Nelumbites to Nelumbo, platanoid inflorescences and Sapindopsis to Platanaceae, and Spanomera to Buxaceae. With the possible exception of Archaeanthus, these fossils are apparently not crown group members of living families but rather stem relatives of one or more families.     

Animal phylogeny: root and branch surgery

Our view of how-many phyla relate to each other is being radically revised by molecular phylogenetics. For example, arthropods and annelids are no longer placed together, but are now considered to be in separate clades. The new tree has important ramifications for developmental biology and genomics.     

A phylogeny of the trimeresurus group of pit vipers: new evidence from a mitochondrial gene tree

The Trimeresurus group is an important radiation of over 40 Asian pit viper species. Once considered congeneric, four genera are generally currently recognized (Trimeresurus sensu stricto, Ovophis, Protobothrops, and Tropidolaemus) but relationships within and between these are still unclear. This study, based on mitochondrial cytochrome b sequences, is the first to include a large number of species (21) and demonstrates that the current taxonomy does not adequately represent either the relationships or the genetic diversity present in the complex. Although many deeper nodes are not strongly supported, the following novel conclusions are all well supported: (1) the paraphyly of Trimeresurus sensu stricto, (2) the presence of several divergent clades within Trimeresurus sensu stricto, (3) the paraphyly of some widespread, medically significant, species, (4) the nonmonophyly of Ovophis, and (5) the monophyly of Protobothrops. Mapping of morphological characters onto the mitochondrial tree further supports the four groups proposed for Trimeresurus sensu stricto.     

A complete styginid trilobite from the Ordovician of Sweden

Styginidae are a small group of trilobite species, which are usually rare and most of which are incompletely known. Here we describe a complete specimen of Raymondaspis grandigena n.sp. from the Middle Ordovician (Darriwilian, upper Arenig) of Sweden. Among the group it has an unusual combination of exceptionally large genal spines, a thorax with notably short pleural spines in the anterior tergites, and a wide concave pygidial margin. The hypostome is documented for the first time in situ in a styginid, and its attachment can be best described as semi-impendent.     

Bride capture,sister exchange and gift marriage among the makuna: A model of marriage exchange

This article explores how notions of power, femininity, and ethnicity permeate the discourses of and around girls involved in gangs. I explore how the cholas ‐ Latina gang girls ‐ of Foxbury perform and inscribe on their bodies a specific kind of femininity that not only confounds wider community notions of how girls should act, dress, and talk, but throws into question the very gendered category that girls are expected to inhabit.     

New notharctine primate fossils from the early Eocene of New Mexico and southern Wyoming and the phylogeny of Notharctinae

Previously undescribed notharctine primate fossils are reported from the early Eocene San Jose Formation, San Juan Basin, New Mexico, and the early Eocene Wasatch Formation, southern Wyoming. These collections include the most complete specimens yet discovered of the poorly known species Copelemur tutus and Copelemur praetutus; the first upper dentitions of Cantius angulatus and Cantius frugivorus from the type area of these taxa; and fossils attributable to two new notharctine species, Copelemur australotutus and Smilodectes gingerichi. These new fossils reveal that current ideas concerning notharctine phylogeny are incorrect. Two major, monophyletic clades are apparent within the subfamily: the tribe Copelemurini, consisting of the genera Copelemur and Smilodectes, and the tribe Notharctini, comprising the genera Cantius, Pelycodus, and Notharctus. Analysis of the paleobiogeographic distribution of the Copelemurini indicates that this clade was limited to more southerly regions of western North America during early Eocene time. Northward migration of more tropical habitats during the late Wasatchian and early Bridgerian in western North America, associated with an overall climatic warming trend through the early and middle Eocene, appears to have allowed several mammalian taxa, including Smilodectes, to extend their ranges northward during this time interval. Such taxa thus possess diachronous distributions and have been partly responsible for the long-standing confusion regarding the biostratigraphic correlation of early Eocene faunas from New Mexico with those from Wyoming. Based on several taxa which are also known from the Wasatchian of Wyoming, the age of the San Jose Formation appears to be middle Wasatchian.     

A model for coding pollen size in reference to phylogeny using examples from the Ebenaceae

Most genetically based features should be available for use in cladistic analysis. Palynologists routinely measure polar (P) and equatorial (E) axes and place pollen into size classes defined by earlier pollen workers. Grouping of pollen into globally arbitrary classes may not correspond to statistically significant differences among the taxa of a study. We propose a model using conventional statistical procedures coupled with data visualization and Monte Carlo simulation. This approach is not a final solution to the general problem of coding continuous characters into discrete states; it is an attempt to address the problems of character state delimitation in pollen morphology. We suggest that the coding of continuous measurement variables (e.g., P, E) into character states should be done following a logical sequence of interactive visualization (2D and 3D) of bivariate frequency distributions including the inspection of prediction and confidence ellipses (e.g., 99%), and use of ANOVA. We illustrate our approach using realistic pollen data sets generated by a computer program (POLSIM) written to perform Monte Carlo sampling from normally distributed statistical populations of polar and equatorial axes. Our model is then applied to an original data set of 4,134 pollen grains from the Ebenaceae, resulting in the coding of the four genera into three character states for pollen size.     

A molecular phylogeny of scaly tree ferns (Cyatheaceae)

Tree ferns recently were identified as the closest sister group to the hyperdiverse clade of ferns, the polypods. Although most of the 600 species of tree ferns are arborescent, the group encompasses a wide range of morphological variability, from diminutive members to the giant scaly tree ferns, Cyatheaceae. This well-known family comprises most of the tree fern diversity (～500 species) and is widespread in tropical, subtropical, and south temperate regions of the world. Here we investigate the phylogenetic relationships of scaly tree ferns based on DNA sequence data from five plastid regions (rbcL, rbcL-accD IGS, rbcL-atpB IGS, trnG-trnR, and trnL-trnF). A basal dichotomy resolves Sphaeropteris as sister to all other taxa and scale features support these two clades: Sphaeropteris has conform scales, whereas all other taxa have marginate scales. The marginate-scaled clade consists of a basal trichotomy, with the three groups here termed (1) Cyathea (including Cnemidaria, Hymenophyllopsis, Trichipteris), (2) Alsophila sensu stricto, and (3) Gymnosphaera (previously recognized as a section within Alsophila) + A. capensis. Scaly tree ferns display a wide range of indusial structures, and although indusium shape is homoplastic it does contain useful phylogenetic information that supports some of the larger clades recognised.     

Transient exposure of root tips to primary and secondary metabolites: Impact on root growth and production of border cells

Here we describe the use of Pisum sativum L. as a model system to measure how short-term treatment of root tips with soluble metabolites can influence root growth and release of root exudates. The results revealed that even a 3-minute exposure of root tips to metabolites normally released from roots into the rhizosphere (e.g. rhamnose, ferulic acid, salicylic acid) can significantly influence root growth without affecting production of border cells and associated exudates. Conversely, products including caffeine, saccharide lactone, and pisatin alter production of border cells, without affecting root growth. Understanding how root-derived and exogenous metabolites can selectively impact root function may yield benefits in crop production, especially in greenhouse agriculture systems where growing roots can be exposed to a significant accumulation of plant exudates.     

Ultrastructural observations of maize root tips following exposure to monensin

Summary Epidermal and outer rootcap cells of maize root tips were treated with the sodium selective ionophore, monensin, and the ultrastructural changes were studied. In the presence of 10^–5 to 10^–3 M monensin, dictyosomes became distorted, cisternae separated from the stack, and secretory vesicles were released. Released secretory vesicles disappeard from the cytoplasm suggesting that their transport to, and fusion with, the plasma membrane was unaffected. Monensin did not inhibit cytoplasmic streaming of the outer rootcap cells. No new secretory vesicles were formed on the remaining dictyosomes or dictyosome fragments. In contrast to results with animal cells, swelling of plant dictyosome cisternae was observed only after fixation in glutaraldehyde-osmium tetroxide and not after fixation in potassium permanganate. Other cell components were not altered structurally by monensin. The effects of monensin on the Golgi apparatus were reversible, and dictyosomes were either repaired or new dictyosomes were formed after the root tips were removed from the monensin.Dictyosomes in epidermal cells reacted in the same manner as those in the rootcap except that numerous secretory vesicles remained in the cytoplasm, mostly in association with dictyosome fragments. Some secretory vesicles increased in size but no evidence of vesicle-vesicle fusion was noted. Cell plate formation was partially inhibited or blocked by monensin.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of this product by the USDA.     

A high-yield procedure for isolation of metaphase chromosomes from root tips ofVicia faba L.

A new method is described for the isolation of large quantities of Vicia faba metaphase chromosomes. Roots were treated with 2.5 mM hydroxyurea for 18 h to accumulate meristem tip cells at the G₁/S interface. After release from the block, the cells re-entered the cell cycle with a high degree of synchrony. A treatment with 2.5 M amiprophos-methyl (APM) was used to accumulate mitotic cells in metaphase. The highest metaphase index (53.9%) was achieved when, 6 h after the release from the hydroxyurea block, the roots were exposed to APM for 4 h. The chromosomes were released from formaldehyde-fixed root tips by chopping with a scalpel in LB01 lysis buffer. Both the quality and the quantity of isolated chromosomes, examined microscopically and by flow cytometry, depended on the extent of the fixation. The best results were achieved after fixation with 6% formaldehyde for 30 min. Under these conditions, 1 · 10⁶ chromosomes were routinely obtained from 30 root tips. The chromosomes were morphologically intact and suitable both for high-resolution chromosome studies and for flow-cytometric analysis and sorting. After the addition of hexylene glycol, the chromosome suspensions could be stored at 4° C for six months without any signs of deterioration.Abbreviations APM amiprophos-methyl - DAPI 4,6-diamidino-2-phenylindole The authors thank Mrs. Jiina Eliáová for her excellent technical assistance and Dr. Slavomir Ondro for the supply of V. faba seeds. A gift sample of APM from the Mobay Corporation (Agricultural Chemicals Division, Kansas City, Mo., USA) is gratefully acknowledged.