bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixtures of Varying Coefficient Models for Longitudinal Data with Discrete or Continuous Nonignorable Dropout
Authors: Hogan Joseph W. , Lin Xihong , Herman Benjamin
Published: December 2004

Summary The analysis of longitudinal repeated measures data is frequently complicated by missing data due to informative dropout. We describe a mixture model for joint distribution for longitudinal repeated measures, where the dropout distribution may be continuous and the dependence between response and dropout is semiparametric. Specifically, we assume that responses follow a varying coefficient random effects model conditional on dropout time, where the regression coefficients depend on dropout time through unspecified nonparametric functions that are estimated using step functions when dropout time is discrete (e.g., for panel data) and using smoothing splines when dropout time is continuous. Inference under the proposed semiparametric model is hence more robust than the parametric conditional linear model. The unconditional distribution of the repeated measures is a mixture over the dropout distribution. We show that estimation in the semiparametric varying coefficient mixture model can proceed by fitting a parametric mixed effects model and can be carried out on standard software platforms such as SAS. The model is used to analyze data from a recent AIDS clinical trial and its performance is evaluated using simulations.
Estimation in Bayesian Disease Mapping
Authors: MacNab Ying C. , Farrell Patrick J. , Gustafson Paul , Wen Sijin
Published: December 2004

SummaryRecent work on Bayesian inference of disease mapping models discusses the advantages of the fully Bayesian (FB) approach over its empirical Bayes (EB) counterpart, suggesting that FB posterior standard deviations of small‐area relative risks are more reflective of the uncertainty associated with the relative risk estimation than counterparts based on EB inference, since the latter fail to account for the variability in the estimation of the hyperparameters. In this article, an EB bootstrap methodology for relative risk inference with accurate parametric EB confidence intervals is developed, illustrated, and contrasted with the hyperprior Bayes. We elucidate the close connection between the EB bootstrap methodology and hyperprior Bayes, present a comparison between FB inference via hybrid Markov chain Monte Carlo and EB inference via penalized quasi‐likelihood, and illustrate the ability of parametric bootstrap procedures to adjust for the undercoverage in the “naive” EB interval estimates. We discuss the important roles that FB and EB methods play in risk inference, map interpretation, and real‐life applications. The work is motivated by a recent analysis of small‐area infant mortality rates in the province of British Columbia in Canada.
Smooth Random Effects Distribution in a Linear Mixed Model
Authors: Ghidey Wendimagegn , Lesaffre Emmanuel , Eilers Paul
Published: December 2004

Summary A linear mixed model with a smooth random effects density is proposed. A similar approach to P‐spline smoothing of Eilers and Marx (1996, Statistical Science11, 89–121) is applied to yield a more flexible estimate of the random effects density. Our approach differs from theirs in that the B‐spline basis functions are replaced by approximating Gaussian densities. Fitting the model involves maximizing a penalized marginal likelihood. The best penalty parameters minimize Akaike's Information Criterion employing Gray's (1992, Journal of the American Statistical Association87, 942–951) results. Although our method is applicable to any dimensions of the random effects structure, in this article the two‐dimensional case is explored. Our methodology is conceptually simple, and it is relatively easy to fit in practice and is applied to the cholesterol data first analyzed by Zhang and Davidian (2001, Biometrics57, 795–802). A simulation study shows that our approach yields almost unbiased estimates of the regression and the smoothing parameters in small sample settings. Consistency of the estimates is shown in a particular case.
Efficient Regression Analysis with Ranked‐Set Sampling
Authors: Chen Zehua , Wang You‐Gan
Published: December 2004

Summary This article is motivated by a lung cancer study where a regression model is involved and the response variable is too expensive to measure but the predictor variable can be measured easily with relatively negligible cost. This situation occurs quite often in medical studies, quantitative genetics, and ecological and environmental studies. In this article, by using the idea of ranked‐set sampling (RSS), we develop sampling strategies that can reduce cost and increase efficiency of the regression analysis for the above‐mentioned situation. The developed method is applied retrospectively to a lung cancer study. In the lung cancer study, the interest is to investigate the association between smoking status and three biomarkers: polyphenol DNA adducts, micronuclei, and sister chromatic exchanges. Optimal sampling schemes with different optimality criteria such as A‐, D‐, and integrated mean square error (IMSE)‐optimality are considered in the application. With set size 10 in RSS, the improvement of the optimal schemes over simple random sampling (SRS) is great. For instance, by using the optimal scheme with IMSE‐optimality, the IMSEs of the estimated regression functions for the three biomarkers are reduced to about half of those incurred by using SRS.
Comparability of Segmented Line Regression Models
Authors: Kim Hyune‐Ju , Fay Michael P. , Yu Binbing , Barrett Michael J. , Feuer Eric J.
Published: December 2004

Summary Segmented line regression models, which are composed of continuous linear phases, have been applied to describe changes in rate trend patterns. In this article, we propose a procedure to compare two segmented line regression functions, specifically to test (i) whether the two segmented line regression functions are identical or (ii) whether the two mean functions are parallel allowing different intercepts. A general form of the test statistic is described and then the permutation procedure is proposed to estimate the p‐value of the test. The permutation test is compared to an approximate F‐test in terms of the p‐value estimation and the performance of the permutation test is studied via simulations. The tests are applied to compare female lung cancer mortality rates between two registry areas and also to compare female breast cancer mortality rates between two states.
Surveillance in Longitudinal Models: Detection of Intrauterine Growth Restriction
Authors: Petzold Max , Sonesson Christian , Bergman Eva , Kieler Helle
Published: December 2004

Summary A new methodology for online detection of intrauterine growth restriction (IUGR) is proposed where traditional methods for statistical surveillance are applied. Here, deficient growth rate is used to detect IUGR instead of the common surrogate measure “small for gestational age” (SGA). Fetal growth is estimated by repeated measurements of symphysis‐fundus (SF) height. At each time point the new method, based on the Shiryaev–Roberts method, is used to evaluate the growth in SF height. We use Swedish data to model a normal growth pattern, which is used to evaluate the capability of the new method to detect IUGR in comparison with a method used in practice today. Results from simulations indicate that the new method performs considerably better than the method used today. We also illustrate the effect of some important factors which influence the detection ability and illuminate the tendency of the method used today to misclassify SGA cases as IUGR.
Bayesian Extrapolation of Space–Time Trends in Cancer Registry Data
Authors: Schmid Volker , Held Leonhard
Published: December 2004

SummaryWe apply a full Bayesian model framework to a dataset on stomach cancer mortality in West Germany. The data are stratified by age group, year, and district. Using an age–period–cohort model with an additional spatial component, our goal is to investigate whether there is evidence for space–time interactions in these data. Furthermore, we will determine whether a period–space or a cohort–space interaction model is more appropriate to predict future mortality rates. The setup will be fully Bayesian based on a series of Gaussian Markov random field priors for each of the components. Statistical inference is based on efficient algorithms to block update Gaussian Markov random fields, which have recently been proposed in the literature.
PRICE DISPERSION IN THE SMALL AND IN THE LARGE: EVIDENCE FROM AN INTERNET PRICE COMPARISON SITE
Authors: Baye Michael R. , Morgan John , Scholten Patrick
Published: December 2004

This paper examines four million daily price observations for more than 1,000 consumer electronics products on the price comparison site http://Shopper.com. We find little support for the notion that prices on the Internet are converging to the ‘law of one price.’ In addition, observed levels of price dispersion vary systematically with the number of firms listing prices. The difference between the two lowest prices (the ‘gap’) averages 23 per cent when two firms list prices, and falls to 3.5 per cent in markets where 17 firms list prices. These empirical results are an implication of a general ‘clearinghouse’ model of equilibrium price dispersion.
ADVERSE SELECTION IN ELECTRONIC MARKETS: EVIDENCE FROM ONLINE STAMP AUCTIONS
Authors: Dewan Sanjeev , Hsu Vernon
Published: December 2004

We analyze adverse selection costs in online stamp auctions, based on a comparison of prices on eBay with those of matched stamps at a specialty stamps auction site in the U.S., Michael Rogers, Inc. (MR), which we know a priori has low quality uncertainty. We find that buyer prices are 10–15% lower on eBay as compared to MR, and the price difference, increases with the value of the stamps. Consistent with this adverse selection discount we find that the seller reputation mechanism on eBay has an economically modest, although statistically significant, effect on auction price and probability of sale.
POST‐CARTEL PRICING DURING LITIGATION
Authors: Harrington Joseph E.
Published: December 2004

Standard methods in the U.S. for calculating antitrust damages in price‐fixing cases are shown to create a strategic incentive for firms to price above the non‐collusive price after the cartel has been dissolved. This results in an overestimate of the but for price and an underestimate of the level of damages. The extent of this upward bias in the but for price is greater, the longer the cartel was in place and the more concentrated the industry.
MERGERS WITH SUPPLY FUNCTIONS
Authors: Akgün Uğur
Published: December 2004

I analyze the equilibrium effects of a merger in an industry when firms compete by submitting supply functions. Under the assumptions that the industry capital stock is fixed and production costs are quadratic and decreasing in capital, I find that any merger results in all firms reducing supply. The decrease in supply by non‐participating firms makes any merger profitable. A merger from a symmetric industry lowers welfare.
The Federal Arbitration System and Australian Economic Performance
Authors: Burgess John
Published: December 2004

Has the Federal arbitration system been a facilitator, a barrier or irrelevant in the twentieth century growth record of Australia? To consider this question, the present review considers the role of wage setting institutions in the growth process. It then goes on to consider the contribution of the arbitration system to Australian economic performance. A number of criteria will be addressed, including inflation, unemployment, allocation of labour, productivity growth and responsiveness to economic shocks. The evidence is inconclusive in terms of a direct relationship between the wage setting decisions of the arbitration system and macroeconomic performance. Nevertheless, there are important institutional features of the arbitration system that are important in shaping the growth path of the Australian economy over the past century.
Geometrical Optics Approach to Markov‐Modulated Fluid Models
Authors: Dominici Diego , Knessl Charles
Published: December 2004

We analyze asymptotically a differential‐difference equation, that arises in a Markov‐modulated fluid model. Here, there are N identical sources that turn on and off, and when on they generate fluid at unit rate into a buffer, which processes the fluid at a rate

c < N. In the steady‐state limit, the joint probability distribution of the buffer content and the number of active sources satisfies a system of

N+ 1 ODEs, that can also be viewed as a differential‐difference equation analogous to a backward/forward parabolic PDE. We use singular perturbation methods to analyze the problem for

N→∞, with appropriate scalings of the two state variables. In particular, the ray method and asymptotic matching are used.
Absolute and Convective Instability for Evolution PDEs on the Half‐Line
Authors: Fokas A. S. , Papageorgiou D. T.
Published: December 2004

We analyze evolution PDEs exhibiting absolute (temporal) as well as convective (spatial) instability. Let ω(k) be the associated symbol, i.e., let

exp[ikx−ω(k)t] be a solution of the PDE. We first study the problem on the infinite line with an arbitrary initial condition

q0(x), where

q0(x) decays as

|x| → ∞. By making use of a certain transformation in the complex k‐plane, which leaves

ω(k) invariant, we show that this problem can be analyzed in an elementary manner. We then study the problem on the half‐line, a problem physically more realistic but mathematically more difficult. By making use of the above transformation, as well as by employing a general method recently introduced for the solution of initial‐boundary value problems, we show that this problem can also be analyzed in a straightforward manner. The analysis is presented for a general PDE and is illustrated for two physically significant evolution PDEs with spatial derivatives up to second order and up to fourth order, respectively. The second‐order equation is a linearized Ginzburg–Landau equation arising in Rayleigh–Bénard convection and in the stability of plane Poiseuille flow, while the fourth‐order equation is a linearized Kuramoto–Sivashinsky equation, which includes dispersion and which models among other applications, interfacial phenomena in multifluid flows.
COLCHICINE‐INDUCED ALTERATIONS IN COLONY DEVELOPMENT IN EUDORINA ELEGANS (VOLVOCALES, CHLOROPHYTA)1
Authors: Gottlieb Bruce , Goldstein Melvin E.
Published: December 2004

Colonies of Eudorina elegans Ehrenberg were treated with a 0.2% colchicine solution for periods of up to 48 h, and a number of alterations were observed in dividing colonies. Nuclear alterations were observed after 20 min of treatment, due to the inhibition of spindle microtubule polymerization. This inhibition resulted in increased ploidy levels, and permanent diploid colonies were obtained. The inhibition of cytoplasmic microtubule polymerization resulted in a number of structural alterations including: unequal cytokinesis of plakeal cells, the partial or complete inhibition of cytokinesis (30 min treatment), production of “stellate” cells (90 min treatment), and the subsequent formation of extra‐cytoplasmic particles around the plakeal cells (3 h treatment). A possible cytoskeletal function of peripherally orient ed microtubules, and the role of the phycoplast microtubules is discussed. In addition, colchicine treatment caused an inhibition of inversion (60 min treatment), an increase in golgi‐associated vesicles, and an excessive production of colonial envelope material (3 h treatment). The latter resulted in the formation of flattened Gonium‐like colonies. The process of inversion is discussed in light of the above results. Chloroplast microtubules, however, were unaffected by colchicine treatment.
NUCLEOTIDE SEQUENCE HOMOLOGY OF SOME ALGAL RIBOSOMAL RNAs1
Authors: Soh Guat Lean , Kochert Gary
Published: December 2004

Radioactively labeled ribosomal RNA from seven species of algae was purified and hybridized to purified DNA from Chlamydomonas reinhardtii Dangeard (Chlorophyta). Delta Tm values for the heterologous RNA‐DNA duplexes were obtained by thermal dissociation; values ranged from 3.9 to 10.9 C. Organisms traditionally considered to be less closely related to C. reinhardtii showed the greatest delta Tm values. Ulothrix fimbriata Bold and Klebsormidium flaccidum (Kütz.) S., M. & Bl., although similar morphologically, showed very different delta Tm values and would not appear to be closely related by these criteria.
CHLORIDE UPTAKE BY ANACYSTIS NIDULANS (CYANOPHYCEAE)1
Authors: Craig Susan R. , Budd Kenneth
Published: December 2004

Anacystis nidulans (Richt.) Drouet & Daily (UTEX 625), grown in batch culture with 0.5% CO2 in air, was supplied with chloride labelled with 36Cl in light and dark. Uptake in light was stimulated relative to uptake in darkness. A single transport system for Cl− with an apparent Km for Cl− of 0.14 mM was identified. Chloride in the cells reached a maximum value after 30–50 min at 25 C. At this point the internal Cl− concentration was calculated to be 60‐fold the external (0.1 mM) in light and 37‐fold in darkness. DCMU (3‐[3,4‐dichlorophenyl]–1, 1‐dime‐thylurea), at concentrations which abolished photosynthetic O2 evolution did not inhibit Cl− uptake in light. Carbonyl cyanide m‐chlorophenyl hydrazone (CCCP), at uncoupling concentrations for photosynthesis and dark respiration, strongly inhibited Cl− uptake in light and darkness. N,N'‐dicyclohexyl carbodiimide (DCCD), an energy transfer inhibitor, inhibited light Cl− uptake more slowly than photosynthesis but had no effect on dark Cl− uptake. It is concluded that Cl− uptake in A. nidulans was active in light and darkness, and that ATP was the probable energy source for transport.
A MORPHOMETRIC STUDY OF LEAD AND COPPER EFFECTS ON DIATOMA TENUE VAR. ELONGATUM (BACILLARIOPHYTA)1
Authors: Sicko‐Goad Linda , Stoermer Eugene F.
Published: December 2004

Polyphosphate bodies containing lead were induced in laboratory cultures of Diatoma tenue var. elongatum Lyngb. by the addition of phosphorus and 0.05 μg‐atoms/l Pb to P deficient medium. Morphometric analysis of cells exposed to Pb showed a significant decrease in number of mitochondria with a concomitant increase in their volume and an increase in membranous organelles in the vacuole compared to phosphorus starved and phosphorus sufficient controls. Exposure of cultures to 0.08 μg‐atoms/l copper resulted in reduction of the number of polyphosphate bodies formed during luxury uptake but no other significant morphological changes in cellular organelles. Ecological implications of the interactions between nutrients and low level trace metal contamination are discussed.
CHLOROPHYLL a:b RATIOS IN MARINE PLANKTONIC ALGAE1
Authors: Wood A. Michelle
Published: December 2004

Chlorophyll a:b ratios for Chlorella capsulata Guillard, Bold & MacEntee, Chlorosarcinopsis halophila Guillard, Bold,& MacEntee, Nannochloris atomus Butcher and Micromonas pusilla (Butcher) Manton & Parke were found to be 1.74, 2.46, 1.89, and 1.53, respectively. Compared to previously published values in marine planktonic algae, these ratios are similar to the average value (2.17, SD = 1.12) reported for 25 species in 15 genera. Both the new data and previously published data support the hypothesis that marine algae have lower chlorophyll a:b ratios than do other chlorophyll b containing plants.
ON THE TAXONOMY OF CALIFORNIA LAMINARIA (PHAEOPHYTA)1
Authors: Druehl Louis D.
Published: December 2004

It is suggested that Laminaria setchellii Silva be retained as a species separate from L. dentigera Kjellman as there is no evidence suggesting they are conspecific. Further, L. saccharina (L.) Lamouroux and L. groenlandica Rosenvinge should also continue to be recognized as valid components of the California flora.
Xxth International Congress of Photogrammetry and Remote Sensing
Authors: Newby Paul R. T. , Woodsford Peter A. , Mills Jon P. , Holland David A. , Tompkinson William , Holmes Adrian J. , Robson Stuart , Aplin Paul , Buckley Simon J. , Mehner Henny
Published: December 2004

The XXth International Congress of Photogrammetry and Remote Sensing was held at the Istanbul Convention and Exhibition Centre (ICEC), Turkey, from 12th to 23rd July 2004. Reports are given on the Congress as a whole, including the General Assembly, some Technical Commission activities and the Congress Exhibition. Papers from the Congress are published in Volume XXXV of the International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences.
Protest Voting in Austria, Denmark, and Norway
Authors: Bergh Johannes
Published: December 2004

The article, in part, aims to provide a framework for analysis of the concept of ‘protest voting’. It addresses two empirical questions by use of this framework. First, which parties benefit from protest voting? Second, what are the main objects of political protest which these voters direct their grievances at? Do they protest against the political system, the political elites, or merely certain policies? The empirical analysis, which is based on data from Austria, Denmark, and Norway, suggests that parties that are in opposition, and that have no immediate chance of gaining a government position, are the ones that benefit from protest voting. Political elites are the most common objects of political protest in these countries.
Minority‐Rule Budgeting under a De Facto Constructive Vote of No Confidence: A Cure for the Norwegian Illness?
Authors: Helland Leif
Published: December 2004

A formal analysis of a possible adjustment in the present voting institutions of the Norwegian parliament is conducted. The analysis is confined to three unitary players in a minority situation. It is argued that such a set‐up represents a fairly accurate description of the present political situation in the Norwegian budget process. The proposed adjustment in the voting institutions leads to something that resembles a de facto constructive vote of no confidence in the budget process. Such an instrument is often said to strengthen a minority government. The formal ana‐lysis shows that the adjusted voting institution selects a Condorcet winner if such a winner exists. If, however, no such winner exists, the minority government is always defeated. The latter finding implies that if a cycle in preferences is present, the adjusted voting institution will amplify the inherent instability. This is in stark contrast to the common claim that institutions help break cycles.
505. Aloe Parvula
Authors: Du Puy David
Published: December 2004

Summary.  Aloe parvula A. Berger, a miniature aloe endemic to Madagascar, is described and illustrated. Its ecology and conservation status are discussed. A typical habitat in the Itremo Massif is shown.
506. Aloe Compressa
Authors: Du Puy David
Published: December 2004

Summary.  Aloe compressa H. Perrier, a miniature aloe endemic to Madagascar, is described and illustrated. Its ecology and conservation status are discussed.
507. Aloe Calcairophila
Authors: Du Puy David
Published: December 2004

Summary.  Aloe calcairophila Reynolds, a miniature aloe, endemic to Madagascar, is described and illustrated. Its ecology and conservation status are discussed. Its habitat on Cipolins dominated by Aloe capitata var cipolinicola, is shown.
510. Angraecum Praestans
Authors: Hermans Johan
Published: December 2004

Summary.  The history, taxonomy, habitat and cultivation of Angraecum praestans Schltr. from Madagascar are discussed. A description is provided.
Conserving Madagascar's Plant Diversity: Kew's Madagascar Threatened Plants  Project
Authors: Britt Adam , Clubbe Colin , Ranarivelo Tianjanahary
Published: December 2004

Summary.  This paper outlines the work of the Madagascar Threatened Plants Project(TPP), partly financed by the Friends of Kew. Several species of orchids, palms and succulents are being studied and propagated as trial subjects. At the same time funds are used to improve the infrastructure of Malagasy Institutions actively involved in plant conservation, and to train post‐graduate students who will be the next generation of Malagasy botanists, conservationists and horticulturists.
Feature
Authors: McIlroy D. , Garton M.
Published: December 2004

The ‘pipe rock’ lithofacies has been much maligned by many generations of undergraduates as being dull. We attempt herein to demonstrate some of the subtleties of the pipe‐rock ecosystem and show that ichnology can be a most useful tool to stratigraphers, sedimentologists and petroleum geologists.
Photoperiod Affects Neuronal Nitric Oxide Synthase and Aggressive Behaviour in Male Siberian Hamsters (Phodopus sungorus)
Authors: Wen J. C. , Hotchkiss A. K. , Demas G. E. , Nelson R. J.
Published: December 2004

Many nontropical animals display physiological and behavioural changes in response to seasonal environmental cues including photoperiod (day length). Male Siberian hamsters (Phodopus sungorus) housed in short photoperiod undergo testicular regression accompanied by reduced circulating testosterone and decreased reproductive behaviour. By contrast to the majority of small mammals studied, aggressive behaviour is elevated in short‐day Siberian hamsters when blood testosterone concentrations are not detectable. Because gonadal steroid hormones influence neuronal nitric oxide synthase (nNOS), and this enzyme has been implicated in aggressive behaviour, we hypothesized that nNOS expression would be decreased in short‐day male Siberian hamsters and negatively correlated with the display of territorial aggression. Adult male Siberian hamsters were individually housed in either long (LD 16 : 8 h) or short (LD 8 : 16 h) photoperiods for 10 weeks. Hamsters were assigned to one of two categories by assessing testicular volume and plasma testosterone values: (i) photoperiodic responsive (i.e. regressed testes and low testosterone concentrations) or (ii) photoperiodic nonresponsive (i.e. testes size and circulating testosterone concentrations equivalent to hamsters maintained in long days). At week 10, aggression was assessed using a resident–intruder test. Latency to initial attack, frequency of attacks and duration of total attacks were recorded during a 10‐min aggression trial. Brains were collected immediately after behavioural testing and stained for nNOS expression using immunohistochemistry. All short day‐housed hamsters were significantly more aggressive than long‐day animals, regardless of gonadal size or testosterone concentrations. Short‐day animals, both reproductively responsive and nonresponsive morphs, also had significantly less nNOS‐immunoreactive cells in the anterior and basolateral amygdaloid areas and paraventricular nuclei compared to long‐day hamsters. Together, these results suggest that seasonal aggression in male Siberian hamsters is regulated by photoperiod, through mechanisms that are likely independent from gonadal steroid hormones.
Analysis of the aliphatic monomer composition of polyesters associated with Arabidopsis epidermis: occurrence of octadeca‐cis‐6, cis‐9‐diene‐1,18‐dioate as the major component
Authors: Bonaventure Gustavo , Beisson Frédéric , Ohlrogge John , Pollard Mike
Published: December 2004

Although the surface waxes from Arabidopsis thaliana leaves and stems have been thoroughly characterized, the monomer composition of the polyesters of the cuticular membrane has not been analyzed. Delipidated Arabidopsis leaves or stems, when depolymerized under conditions to cleave polyesters, produced typical ω–hydroxy fatty acid cutin monomers such as 16‐hydroxy‐palmitate, 10,16‐dihydroxy‐palmitate and 18‐hydroxy‐9,10‐epoxy‐stearate. However, the major monomer was octadeca‐cis‐6, cis‐9‐diene‐1,18‐dioate, with lesser amounts of octadec‐cis‐9‐ene‐1,18‐dioate and hexadeca‐1,16‐dioate. These dicarboxylates were found predominantly in epidermal peels from Arabidopsis stems and are therefore likely to be associated with the cuticular membrane. They were also found in analyses of canola leaves but were absent in tomato and apple fruit cutins. In the fad2‐1 mutant line of Arabidopsis, which has reduced levels of linoleate and linolenate and elevated oleate in cytosolic phospholipids, the amount of octadeca‐cis‐6, cis‐9‐diene‐1,18‐dioate was 50% reduced, with a concomitant increase in octadec‐cis‐9‐ene‐1,18‐dioate. In a fatb‐ko line of Arabidopsis, where the availability of cytosolic palmitate is impaired, there was an 80% loss of C16 monomers and a compensating increase in C18 monomers. The presence of substantial amounts of dicarboxylates in cuticular membranes is unexpected. High amounts of aliphatic dicarboxylates are usually considered as an indicator of suberin, and are reported only as very minor components of cutin. The high level of polyunsaturation is also unusual in cuticles; saturated fatty acid monomers usually predominate, with lesser amounts of monounsaturates. These novel findings for Arabidopsis demonstrate that a broad range of monomer compositions are possible for polyesters of the epidermis.
Comparison of TRY and the closely related At1g01380 gene in controlling Arabidopsis trichome patterning
Authors: Esch Jeffrey J. , Chen Margaret A. , Hillestad Matthew , David Marks M.
Published: December 2004

A screen of activation‐tagged Arabidopsis lines resulted in the identification of At1g01380, which encodes a small R3 single repeat MYB gene, as a negative regulator of trichome initiation. Plants that overexpress this gene have fewer trichomes. The gene is closely related to the previously identified negative regulator TRY, and has a similar pattern of expression as TRY in developing leaves. As previously shown for TRY, At1g01380 protein can inhibit the interaction between the positive trichome regulators GL1 and GL3, and likely limits trichome initiation via this inhibition. While TRY and At1g01380 are closely related, they are not completely functionally equivalent. When placed under the transcriptional control of the TRY promoter, At1g01380 can only partially rescue the try mutant. Interestingly, Atg01380 is highly expressed in gl3‐sst trichomes, while TRY expression is greatly reduced. The mutation in gl3‐sst causes a reduced interaction between the GL1 and GL3 proteins and results in fewer leaf trichomes that develop in clusters. The differential expression of TRY and At1g01380 in this mutant can be used to explain how its altered trichome pattern in gl2‐sst is generated.
Arabidopsis glucosyltransferase UGT74B1 functions in glucosinolate biosynthesis and auxin homeostasis
Authors: Douglas Grubb C. , Zipp Brandon J. , Ludwig‐Müller Jutta , Masuno Makoto N. , Molinski Tadeusz F. , Abel Steffen
Published: December 2004

Glucosinolates are a class of secondary metabolites with important roles in plant defense and human nutrition. Here, we characterize a putative UDP‐glucose:thiohydroximate S‐glucosyltransferase, UGT74B1, to determine its role in the Arabidopsis glucosinolate pathway. Biochemical analyses demonstrate that recombinant UGT74B1 specifically glucosylates the thiohydroximate functional group. Low Km values for phenylacetothiohydroximic acid (approximately 6 μm) and UDP‐glucose (approximately 50 μm) strongly suggest that thiohydroximates are in vivo substrates of UGT74B1. Insertional loss‐of‐function ugt74b1 mutants exhibit significantly decreased, but not abolished, glucosinolate accumulation. In addition, ugt74b1 mutants display phenotypes reminiscent of auxin overproduction, such as epinastic cotyledons, elongated hypocotyls in light‐grown plants, excess adventitious rooting and incomplete leaf vascularization. Indeed, during early plant development, mutant ugt74b1 seedlings accumulate nearly threefold more indole‐3‐acetic acid than the wild type. Other phenotypes, however, such as chlorosis along the leaf veins, are likely caused by thiohydroximate toxicity. Analysis of UGT74B1 promoter activity during plant development reveals expression patterns consistent with glucosinolate metabolism and induction by auxin treatment. The results are discussed in the context of known mutations in glucosinolate pathway genes and their effects on auxin homeostasis. Taken together, our work provides complementary in vitro and in vivo evidence for a primary role of UGT74B1 in glucosinolate biosynthesis.
Mutations in PMR5 result in powdery mildew resistance and altered cell wall composition
Authors: Vogel John P. , Raab Theodore K. , Somerville Chris R. , Somerville Shauna C.
Published: December 2004

Powdery mildews and other obligate biotrophic pathogens are highly adapted to their hosts and often show limited host ranges. One facet of such host specialization is likely to be penetration of the host cell wall, a major barrier to infection. A mutation in the pmr5 gene rendered Arabidopsis resistant to the powdery mildew species Erysiphe cichoracearum and Erysiphe orontii, but not to the unrelated pathogens Pseudomonas syringae or Peronospora parasitica. PMR5 belongs to a large family of plant‐specific genes of unknown function. pmr5‐mediated resistance did not require signaling through either the salicylic acid or jasmonic acid/ethylene defense pathways, suggesting resistance in this mutant may be due either to the loss of a susceptibility factor or to the activation of a novel form of defense. Based on Fourier transform infrared analysis, the pmr5 cell walls were enriched in pectin and exhibited a reduced degree of pectin modification relative to wild‐type cell walls. In addition, the mutant had smaller cells, suggesting a defect in cell expansion. A double mutant with pmr6 (defective in a glycosylphosphatidylinositol‐anchored pectate lyase‐like gene) exhibited a strong increase in total uronic acid content and a more severe reduction in size, relative to the single mutants, suggesting that the two genes affect pectin composition, either directly or indirectly, via different mechanisms. These two mutants highlight the importance of the host cell wall in plant–microbe interactions.
Loss of TIP1;1 aquaporin in Arabidopsis leads to cell and plant death
Authors: Ma Shisong , Quist Tanya M. , Ulanov Alexander , Joly Robert , Bohnert Hans J.
Published: December 2004

Arabidopsis TIP1;1 (γTIP) is a member of the tonoplast family of aquaporins (AQP). Using RNA interference (RNAi) we reduced TIP1;1 to different extent in various lines. When most severely affected, miniature plants died, a phenotype partially complemented by the TIP1;1 homolog McMIP‐F. Less severely affected lines produced small plants, early senescence, and showed lesion formation. The relative water content in TIP1;1 RNAi plants was not significantly affected. Global expression profiling suggested a disturbance in carbon metabolism in RNAi lines with upregulated transcripts for functions in carbon acquisition and respiration, vesicle transport, signaling and transcription, and radical oxygen stress. Metabolite profiles showed low glucose, fructose, inositol, and threonic, succinic, fumaric, and malic acids, but sucrose levels were similar to WT. Increased amounts were found for raffinose and several unknown compounds. TIP1;1 RNAi plants also contained high starch and apoplastic carbohydrate increased. A GFP‐TIP1;1 fusion protein indicated tonoplast location in spongy mesophyll cells, and high signal intensity in palisade mesophyll associated with vesicles near plastids. Signals in vascular tissues were strongest not only in vesicle‐like structures but also outlined large vacuoles. Compromised routing of carbohydrate and lack of sucrose provision for cell‐autonomous functions seems to characterize this RNAi phenotype. We suggest a function for TIP1;1 in vesicle‐based metabolite routing through or between pre‐vacuolar compartments and the central vacuole. Phenotype and expression characteristics support a view of TIP1;1 functioning as a marker for vesicles that are targeted to the central vacuole.
Endogenous salicylic acid protects rice plants from oxidative damage caused by aging as well as biotic and abiotic stress
Authors: Yang Yinong , Qi Min , Mei Chuansheng
Published: December 2004

Salicylic acid (SA) is a key endogenous signal that mediates defense gene expression and disease resistance in many dicotyledonous species. In contrast to tobacco and Arabidopsis, which contain low basal levels of SA, rice has two orders of magnitude higher levels of SA and appears to be insensitive to exogenous SA treatment. To determine the role of SA in rice plants, we have generated SA‐deficient transgenic rice by expressing the bacterial salicylate hydroxylase that degrades SA. Depletion of high levels of endogenous SA in transgenic rice does not measurably affect defense gene expression, but reduces the plant's capacity to detoxify reactive oxygen intermediates (ROI). SA‐deficient transgenic rice contains elevated levels of superoxide and H2O2, and exhibits spontaneous lesion formation in an age‐ and light‐dependent manner. Exogenous application of SA analog benzothiadiazole complements SA deficiency and suppresses ROI levels and lesion formation. Although an increase of conjugated catechol was detected in SA‐deficient rice, catechol does not appear to significantly affect ROI levels based on the endogenous catechol data and exogenous catechol treatment. When infected with the blast fungus (Magnaporthe grisea), SA‐deficient rice exhibits increased susceptibility to oxidative bursts elicited by avirulent isolates. Furthermore, SA‐deficient rice is hyperresponsive to oxidative damage caused by paraquat treatment. Taken together, our results strongly suggest that SA plays an important role to modulate redox balance and protect rice plants from oxidative stress.
Gene shuffling‐generated and natural variants of the tomato resistance gene Cf‐9 exhibit different auto‐necrosis‐inducing activities in Nicotiana species
Authors: Wulff Brande B.H. , Kruijt Marco , Collins Peter L. , Thomas Colwyn M. , Ludwig Andrea A. , De Wit Pierre J.G.M. , Jones Jonathan D.G.
Published: December 2004

Tomato Cf genes encode membrane‐bound proteins with extracellular leucine‐rich repeats, and confer resistance to the fungal tomato pathogen Cladosporium fulvum, and a hypersensitive response (HR) to C. fulvum‐derived race‐specific elicitors. Several Cf genes, including Cf‐4 and Cf‐9, are members of the highly homologous Hcr9 (homologues of C. fulvumresistance gene Cf‐9) gene family. Hcr9s evolve mainly by sequence exchange between paralogues, by which novel Cf genes may be generated. To mimic this aspect of natural evolution, we generated chimeras between multiple Hcr9s in vitro by gene shuffling. The shufflants were tested for novel specificities by transient expression in Nicotiana benthamiana. Many shufflants induced an HR in the absence of fungal elicitors and were designated auto‐activators. We also identified two natural Hcr9 auto‐activators in the wild tomato species Lycopersicon peruvianum, which induced an HR upon expression in N. benthamiana. The Hcr9 auto‐activators exhibit different auto‐necrosis‐inducing specificities in five selected species of the Nicotiana genus, and they were shown to function in the same signalling pathway as Cf‐9. Auto‐activating alleles of nucleotide binding site–leucine‐rich repeat genes and the protein kinase Pto were previously described. The auto‐activators described here, belonging to the Cf‐like structural class of resistance genes, shed light on this important phenotype and may be used as tools to unravel the mechanisms by which this class of resistance proteins function.
A retrospective study comparing the histopathological features and response to treatment in two canine nasal dermatoses, DLE and MCP
Authors: WIEMELT S. P. , GOLDSCHMIDT M. H. , GREEK J. S. , JEFFERS J. G. , WIEMELT A. P. , MAULDIN E. A.
Published: December 2004

Abstract  Canine discoid lupus erythematosus (DLE) and mucocutaneous pyoderma (MCP) have overlapping clinical and histopathological changes, often making diagnosis difficult. Histopathological features of 27 nasal planum biopsies were scored to determine whether DLE and MCP were histopathologically distinguishable. Long‐term follow‐up, enabling assessment of clinical diagnoses, was available on 15 cases; 11/15 cases were immunomodulatory responsive (ImR) and 4/15 were antibiotic responsive (AbR). Clinical diagnosis, determined by response to treatment for 15/27 cases, was not predictable based on scoring of histopathological features. Distinct histopathological patterns were observed: 2/11 ImR cases had a lymphocyte‐rich interface dermatitis. All other cases had the same histopathological changes: a band‐like diffuse superficial plasmacytic to lymphoplasmacytic dermatitis ± focal basal cell damage, but different clinical diagnoses (4/4 AbR, 9/11 ImR). German shepherd dogs/crosses were over‐represented (44.4% of the cases) and tended to have more multifocal lesions (41.7% vs. 26.7% of all other breeds). Longer duration of disease was associated with a preponderance of plasmacytic infiltrate (P = 0.026).
Temporal Shifts in Conspicuousness: Mate Attraction Displays of the Texas Field Cricket, Gryllus texensis
Authors: Bertram Susan M. , Xochitl Orozco S. , Bellani Rudy
Published: December 2004

Conspicuous mate attraction displays can simultaneously draw the attention of potential mates and predators, placing the signaller in peril of becoming prey. The balance between these countervailing forms of selection has the potential to shape mate attraction displays. Male Texas field crickets (Gryllus texensis; Orthoptera) signal acoustically to attract mates. Mating signals also attract acoustically orienting parasitoid flies (Ormia ochracea; Tachinidae). Both the abundance of female crickets and parasitoid flies fluctuates throughout the night. We show mate attraction displays exhibit diel shifts that correlate positively with expected female cricket presence and negatively with expected parasitoid fly activity. During early evening, when parasitoids are most common and mating is scarce, crickets signal less often and with reduced conspicuousness. During the second half of the evening, when sexually receptive females are abundant and parasitoids are scarce, crickets signal more often and with enhanced conspicuousness. These diel shifts in mate attraction displays do not appear to result from male crickets detecting parasitoid flies or female crickets and altering their behaviour accordingly. Males in close proximity to parasitoid flies or female crickets do not signal differently than lone males. Instead, diel pattern shifts in mate attraction displays appear to be a selective response to trade‐offs between natural selection via parasitism and sexual selection via mate choice.
Predatory Attacks to the Head vs. Body Modify Behavioral Responses of Garter Snakes
Authors: Langkilde Tracy , Shine Richard , Mason Robert T.
Published: December 2004

An animal's response to predatory attack may depend upon which part of its body is the focus of that attack, because of differential vulnerability to injury. Many avian and mammalian predators direct attacks preferentially toward the prey's head, so simulated attacks that do not have this focus may elicit non‐natural responses. We ‘pecked’ 152 free‐ranging adult male garter snakes (Thamnophis sirtalis parietalis) in Manitoba either on the head or the midbody, and recorded their responses. The snakes’ antipredator tactics were affected not only by body size (larger snakes performed threat displays more often) and body temperature (hotter snakes were more likely to flee), but also by location of the attack. Pecks to the head generally resulted in snakes coiling and hiding their heads, often simultaneously elevating and wriggling their tails in an apparent distraction display. In contrast, pecks to the midbody stimulated either escape responses, or (in snakes that did not flee) open‐mouthed threat displays. More generally, antipredator tactics may respond in flexible ways to details of the predator–prey encounter (including attributes of the habitat as well as the morphology and behavior of both participants) and hence, experimental studies need to carefully simulate such details. The part of the body under attack may be an important factor in this respect.
Immediate and Delayed Benefits of Play Behaviour: New Evidence from Chimpanzees (Pan troglodytes)
Authors: Palagi E. , Cordoni G. , Borgognini Tarli S. M.
Published: December 2004

Evidence for the anticipation of competition at feeding time has been previously documented in both Pan species. Chimpanzees seem to cope with competitive tendency through behavioural mechanisms of tension reduction, and grooming is certainly one of these. Social play and grooming are often matched because they bring animals into close physical contact for long periods, and they have an important role in social cohesion. Our goal was to investigate the occurrence of play behaviour during the pre‐feeding period, before a basic maintenance activity is about to take place, in the chimpanzee colony housed in the ZooParc de Beauval (St Aignan sur Cher, France). The group was composed of 10 adults and nine immature individuals. By scan animal sampling (344 h of observation), we recorded play and grooming interactions in all age‐class combinations during four different periods (pre‐feeding, feeding, post‐feeding, control). We found peak levels of grooming interactions among adults during the pre‐feeding time. A peak frequency at the pre‐feeding time was also found in social play between adults and unrelated immature subjects. This finding suggests that during high tension periods, grooming and play might share similar functions in conflict management. Like grooming, play might have an important role to limit aggression and increase tolerance around food (immediate benefits). Immature animals showed a higher frequency of play in the pre‐feeding than in any other condition (feeding, post‐feeding, and control). During high excitement periods social play probably represents a safe mechanism for immature subjects to test their personal abilities (self‐assessment), the strength/weakness of playmates, and the degree of cooperation/competition with them (social‐assessment). In the light of this new evidence, we can assert that play behaviour is far from being a purposeless activity, at least in the chimpanzee colony under study.
The Ontogeny of Spatio‐Temporal Tactics and Social Relationships of Adult Male Iberian Rock Lizards, Lacerta monticola
Authors: Aragón Pedro , López Pilar , Martín José
Published: December 2004

Behavioural aspects of many species may change through their ontogenetic trajectory. Mature males of the lizard Lacerta monticola present two types of colour phase, with bright green males being older, larger and more dominant than dull brown males. We hypothesized those ontogenetic differences in males’ competitive ability may lead to differences in spatio‐temporal tactics. In a field study, we did not find differences in the size of the home ranges or core areas of green and brown males. However, after controlling for size, green males had more exclusive areas than brown males. Green males also had higher levels of conspicuous activities than brown males. Green and brown males had different spatio‐temporal tactics within the day; green males used their home ranges more, were more active and had a higher degree of overlap with other males in the morning than in the afternoon. Brown males did not show these variations through the day. Green males participated in, and won more intrasexual agonistic interactions. Also, green males overlapped more extensively with areas of potential mates, and guarded females more often than brown males. These behavioural differences between males showed plasticity through ontogeny in the use of space, time and types of activity.