bluuebunny/crossref_metadata_2025 huggingface dataset:
High salinity alters chloroplast morpho‐physiology in a freshwater Kirchneriella species (Selenastraceae) from Ethiopian Lake Awasa
Authors: Ferroni Lorenzo , Baldisserotto Costanza , Pantaleoni Laura , Billi Paolo , Fasulo Maria P. , Pancaldi Simonetta
Published: February 2008

Plants differ in their ability to tolerate salt stress. In aquatic ecosystems, it is important to know the responses of microalgae to increased salinity levels, especially considering that global warming will increase salinity levels in some regions of the Earth, e.g., Ethiopia. A green microalga, Kirchneriella sp. (Selenastraceae, Chlorophyta), isolated from freshwater Lake Awasa in the Rift Valley, Ethiopia, was cultured in media amended with 0, 0.4, 1.9, 5.9, and 19.4 g NaCl·L−1 adjusted with NaCl to five salinity levels adjusted with NaCl. Growth was monitored for 3 mo, then samples were collected for photosynthetic pigment determinations, microspectrofluorimetric analyses, and micro‐ and submicroscopic examinations. The best growth was found at 1.9 g NaCl·L−1. In the chloroplast, excess NaCl affected the coupling of light harvesting complex II and photosystem II (LHCII‐PSII), but changes in thylakoid architecture and in the PSII assembly state allowed sufficient integrity of the photosynthetic membrane. The mucilaginous capsule around the cell probably provided partial protection against NaCl excess. On the whole, the microalga is able to acclimate to a range of NaCl concentrations, and this plasticity indicates that Kirchneriella sp. may survive future changes in water quality.
Phylogenetic evidence for a flower size and number trade‐off
Authors: Sargent Risa D. , Goodwillie Carol , Kalisz Susan , Ree Richard H.
Published: February 2008

The size and number of flowers displayed together on an inflorescence (floral display) influences pollinator attraction and pollen transfer and receipt, and is integral to plant reproductive success and fitness. Life history theory predicts that the evolution of floral display is constrained by trade‐offs between the size and number of flowers and inflorescences. Indeed, a trade‐off between flower size and flower number is a key assumption of models of inflorescence architecture and the evolution of floral display. Surprisingly, however, empirical evidence for the trade‐off is limited. In particular, there is a lack of phylogenetic evidence for a trade‐off between flower size and number. Analyses of phylogenetic independent contrasts (PICs) of 251 angiosperm species spanning 63 families yielded a significant negative correlation between flower size and flower number. At smaller phylogenetic scales, analyses of individual genera did not always find evidence of a trade‐off, a result consistent with previous studies that have examined the trade‐off for a single species or genus. Ours is the first study to support an angiosperm‐wide trade‐off between flower size and number and supports the theory that life history constraints have influenced the evolution of floral display.
Multiscale analysis of Hymenocallis coronaria (Amaryllidaceae) genetic diversity, genetic structure, and gene movement under the influence of unidirectional stream flow
Authors: Markwith Scott H. , Scanlon Michael J.
Published: February 2008

Understanding gene movement patterns in unidirectional flow environments and their effect on patterns of genetic diversity and genetic structure is necessary to manage these systems. Hypotheses and models to explain genetic patterns in streams are rare, and the results of macrophyte studies are inconsistent. This study addresses Ritland's (Canadian Journal of Botany 67: 2017–2024) unidirectional diversity hypothesis, the one‐dimensional stepping stone model, and the metapopulation model within and among populations. Hymenocallis coronaria, an aquatic macrophyte of rocky river shoals of the SE USA, was sampled in four river basins. Within populations and among populations <16.2 km apart had significant isolation by distance. However, the rate of gene flow decay was not consistent with a one‐dimensional stepping stone model, nor was evidence strong or consistent for Ritland's hypothesis. Some evidence indicates that localized metapopulation processes may be affecting genetic diversity and structure; however, gene flow patterns inconsistent with the assumptions of the linear and unidirectional models are also a possible influence. We discuss three variants on the one‐dimensional stepping stone model. Future research in linear environments should examine the expectations of these models. This study is also one of the first efforts to calculate population genetic parameters using a new program, TETRASAT.
Testing implicit assumptions regarding the age vs. size dependence of stem biomechanics usingPittocaulon(Senecio)praecox(Asteraceae)
Authors: Rosell Julieta A. , Olson Mark E.
Published: February 2008

Strong covariation between organismal traits is often taken as an indication of a potentially adaptively significant relationship. Because one of the main functions of woody stems is mechanical support, identifying the factors that covary with biomechanics is essential for inference of adaptation. To date in such studies, stem biomechanics is plotted against stem age or size, thus with implicit assumptions regarding the importance of each in determining mechanics. Likewise, comparing ontogenies between individuals is central to the study of ontogenetic evolution (e.g., heterochrony). Both absolute age and size have been used, but the rationale for choosing one over the other has not been examined. Sampling a plant of simple architecture across microsites with differing sizes for the same absolute age, we compared regressions of stem length, mechanics, and tissue areas against age and size. Stem length was predicted by diameter but not by age, and stem biomechanics and tissue areas were better explained by stem length rather than age. We show that the allometric and mechanical properties observed across microsites are uniform despite great plasticity in other features (e.g., size and wood anatomy) and suggest that this uniformity is an example of developmental homeostasis. Finally, we discuss reasons for preferring size over absolute age as a basis for comparing ontogenies between individuals.
The origin and number of introductions of the Hawaiian endemic Silene species (Caryophyllaceae)
Authors: Eggens Frida , Popp Magnus , Nepokroeff Molly , Wagner Warren L. , Oxelman Bengt
Published: February 2008

The Hawaiian endemic Silene are a small group of woody or semiwoody representatives from a large, predominantly herbaceous, species‐rich genus. We here investigated the origin and number of introductions of the endemic Hawaiian Silene based on phylogenetic relationships inferred from DNA sequences from both the plastid (the rps16 intron) and the nuclear (ribosomal internal transcribed sequences, ITS, and intron 23 of the RPB2 gene) genomes. Silene antirrhina, a widespread weedy American annual, is strongly supported as sister to a monophyletic group consisting of the Hawaiian Silene, indicating a single colonization event. There are no obvious morphological similarities between S. antirrhina and any of the species of Hawaiian Silene. Our results suggest an American origin for the Hawaiian endemics because that would require only a single trans‐ocean dispersal. Two of the Hawaiian endemics (S. struthioloides and S. hawaiiensis) that form a subclade in the analyses have evolved woodiness after introduction to the Hawaiian Islands. Our results contribute to other recent results based on molecular phylogenetics that emphasize the American continent as a source area for the Hawaiian flora and support a striking morphological radiation and evolution of woodiness from a single introduction to the archipelago.
Reproductive ecology of a federally endangered legume, Baptisia arachnifera, and its more widespread congener, B. lanceolata (Fabaceae)
Authors: Young Amy S. , Chang Shu‐Mei , Sharitz Rebecca R.
Published: February 2008

Comparisons between rare species and their more common congener species can provide valuable information for conservation. Reproductive traits have previously been shown to be critical for reproductive success and persistence of rare species. In this study, we compared floral, seedpod, and seed traits of two Baptisia species (one endangered and one common) to assess differences in reproduction between species and among populations. Because heat can trigger germination in hard‐seeded legumes, we also exposed Baptisia seeds to a range of high temperatures (60–100°C) and determined seed viability. The rare Baptisia arachnifera had significantly greater pod damage by insects and produced significantly fewer, yet heavier, seeds than B. lanceolata. While B. arachnifera seeds were seldom viable at temperatures above 80°C, approximately 40% of B. lanceolata seeds maintained viability up to 100°C. Our various seed trait measurements suggest that B. arachnifera may be a poorer colonizer than the more widespread B. lanceolata. Additionally, B. arachnifera's reduced tolerance for high temperatures may have implications for appropriate fire management regimes for this endangered species.
Do differences in plant and flower age change mating patterns and alter offspring fitness in Raphanus sativus (Brassicaceae)?
Authors: Marshall Diane L. , Reynolds Jerusha , Abrahamson Nathan J. , Simpson Heather L. , Barnes Melanie G. , Medeiros Juliana S. , Walsh Sharon , Oliveras Diana M. , Avritt Joy J.
Published: February 2008

When more pollen is present on stigmas than needed to fertilize all ovules, selection among pollen grains may occur due to effects of both pollen donors and maternal plants. We asked whether increasing plant age and flower age, two changes in maternal condition, altered the pattern of seed paternity after mixed pollination. We also asked whether changes in seed paternity affected offspring success in an experimental garden. While flower age did not affect seed paternity, there was a dramatic shift in pollen donor performance as plants aged. These differences were seen in the offspring as well, where the offspring of one pollen donor, which sired more seeds on young plants, flowered earlier in the season, and the offspring of another pollen donor, which sired more seeds on old plants, flowered later in the season. Thus, change in maternal condition resulted in altered seed paternity, perhaps because the environment for pollen tube growth was different. The pattern of seed paternity and offspring performance suggests that pollen donors may show temporal specialization.
Phenotypic integration and the potential for independent color evolution in a polymorphic spring ephemeral
Authors: Frey Frank M.
Published: February 2008

The genetic architecture of the total phenotype may substantially constrain or enhance the evolution of floral color within populations in response to multiple selection pressures. Using Claytonia virginica I previously identified opposing selection on floral color generated through herbivores and pathogens. Here I ask whether the evolution of floral color in this system is constrained or unconstrained by its phenotypic integration with floral and vegetative traits. Morphological, physiological, and pollen traits were measured on over 400 plants in the field and greenhouse, and these data were used to test whether floral‐color morphs differed with respect to other traits and whether the among‐trait correlation structure differed across the color morphs. The color morphs varied with respect to most measured traits; however, the pattern of variation was not consistent among them, and there was little evidence of trade‐offs with floral color. A common principal components analysis revealed that the pattern of phenotypic integration substantially differed among the color morphs. Combined, these results suggest that floral‐color evolution may proceed relatively unconstrained by associations with other traits in this system. The absence of a strong constraint in combination with known fluctuating selective pressures may help to explain observed within‐ and among‐population color variation in this species.
Phenotypic plasticity, precipitation, and invasiveness in the fire‐promoting grass Pennisetum setaceum (Poaceae)
Authors: Poulin Jessica , Sakai Ann K. , Weller Stephen G. , Nguyen Tan
Published: February 2008

Invasiveness may result from genetic variation and adaptation or phenotypic plasticity, and genetic variation in fitness traits may be especially critical. Pennisetum setaceum (fountain grass, Poaceae) is highly invasive in Hawaii (HI), moderately invasive in Arizona (AZ), and less invasive in southern California (CA). In common garden experiments, we examined the relative importance of quantitative trait variation, precipitation, and phenotypic plasticity in invasiveness. In two very different environments, plants showed no differences by state of origin (HI, CA, AZ) in aboveground biomass, seeds/flower, and total seed number. Plants from different states were also similar within watering treatment. Plants with supplemental watering, relative to unwatered plants, had greater biomass, specific leaf area (SLA), and total seed number, but did not differ in seeds/flower. Progeny grown from seeds produced under different watering treatments showed no maternal effects in seed mass, germination, biomass or SLA. High phenotypic plasticity, rather than local adaptation is likely responsible for variation in invasiveness. Global change models indicate that temperature and precipitation patterns over the next several decades will change, although the direction of change is uncertain. Drier summers in southern California may retard further invasion, while wetter summers may favor the spread of fountain grass.
Molecular insights into the taxonomy ofGlyceria(Poaceae: Meliceae) in North America
Authors: Whipple Ian G. , Barkworth Mary E. , Bushman Bradley S.
Published: February 2008

EighteenGlyceriaspecies grow in the United States and Canada, with 16 being native to the region. We used data from morphology and three chloroplast DNA intergenic regions to address taxonomic questions concerningGlyceriain North America, particularly the status ofG. declinata,G. occidentalis,G. fluitans,G. striata, andG. elatain western North America. The chloroplast data confirmed the presence of two European species,G. declinataandG. fluitans, in western North America.Glyceria occidentaliswas exceptional among the taxa studied in having chloroplast genotypes that fell into two different clades, one of which containedG. fluitansand the other the North American speciesG. leptostachya. The morphological data showedG. occidentalisto be intermediate betweenG. fluitansandG. leptostachyawith respect to their distinguishing characters. Based on these results, we hypothesize thatG. occidentalisconsists of hybrids betweenG. fluitansandG. leptostachya.Glyceria elataandG. striata, which have sometimes been treated as a single species, had different chloroplast genotypes, supporting their recognition as distinct taxa. DNA data from all three intergenic regions would be needed for unequivocal identification of the non‐hybrid species examined.
Does Macaronesia exist? Conflicting signal in the bryophyte and pteridophyte floras
Authors: Vanderpoorten A. , Rumsey F. J. , Carine M. A.
Published: February 2008

Macaronesia, which includes five mid‐Atlantic archipelagos (Azores, Madeira, Selvagems, Canaries, and Cape Verdes), has been traditionally recognized as a distinct biogeographic unit whose circumscription has been intimately associated with the hypothesis that the flora is a relict of a formerly broadly distributed subtropical Tertiary flora. The concept of Macaronesia is revisited here using parsimony and Bayesian analyses of floristic data sets for the moss, liverwort, and pteridophyte floras. All analyses reject the monophyly of Macaronesia s.l., resolving the Cape Verdes with tropical Africa. Of the other Macaronesian archipelagos, the liverwort and pteridophyte analyses support, or could not reject, an Azorean‐Madeiran‐Canarian clade (hereafter Macaronesia s.s.), but the moss analysis resolves the Canary Islands as sister to North Africa, thus rejecting the concept of Macaronesia s.s. for this group. Dynamic interchange of taxa with neighboring continental areas rather than relictualism best explains the relationships of the Cape Verde cryptogamic flora and the Canary Island moss flora. In contrast, relictualism is consistent with a monophyletic Macaronesia s.s. for liverworts and pteridophytes. However, from the limited information available on relationships of endemic cryptogams, this explanation alone may be unsatisfactory. Spatially congruent patterns may, in fact, conceal a complex mixture of relictual distributions and more recent speciation and dispersal events.
Elevated temperatures increase leaf senescence and root secondary metabolite concentrations in the understory herb Panax quinquefolius (Araliaceae)
Authors: Jochum Gera M. , Mudge Kenneth W. , Thomas Richard B.
Published: February 2008

The response of understory species to elevated temperatures is not well understood but is important because these plants are highly sensitive to their growth conditions. Three‐year‐old plants of Panax quinquefolius, an understory herb endemic to the eastern deciduous forests of North America, were grown in a greenhouse at 25/20°C (day/night) or 30/25°C for one growing season and analyzed each month. Plants grown at high temperatures had an early onset of leaf senescence and therefore accumulated less carbon. From May to July, P. quinquefolius grown at high temperatures had decreased photosynthesis (52%), stomatal conductance (60%), and root and total biomass (33% and 28%, respectively) compared to plants grown at low temperatures. As P. quinquefolius prepared to overwinter, plants grown at high temperatures had less root biomass (53%) than plants in low temperatures. The amount of storage‐root ginsenosides was unaffected by temperature, and differences in storage root size may explain why plants grown at high temperatures had greater concentrations of storage root ginsenosides (49%) than plants grown at low temperatures. Panax quinquefolius is clearly sensitive to a 5°C increase in temperature, and therefore other understory species may be negatively impacted by future increases in global temperature.
Molecular phylogeny of Nyctaginaceae: taxonomy, biogeography, and characters associated with a radiation of xerophytic genera in North America
Authors: Douglas Norman A. , Manos Paul S.
Published: February 2008

The four o'clock family (Nyctaginaceae) has a number of genera with unusual morphological and ecological characters, several of which appear to have a “tendency” to evolve repeatedly in Nyctaginaceae. Despite this, the Nyctaginaceae have attracted little attention from botanists. To produce a phylogeny for the Nyctaginaceae, we sampled 51 species representing 25 genera (of 28–31) for three chloroplast loci (ndhF, rps16, rpl16, and nrITS) and included all genera from North America. Parsimony, likelihood, and Bayesian methods were used to reconstruct the phylogeny for the family. The family is neotropical in origin. A radiation of woody taxa unites Pisonia and Pisoniella with the difficult tropical genera Neea and Guapira, which also form a clade, though neither appears to be monophyletic. This group is sister to a clade containing Bougainvillea, Belemia, and Phaeoptilum. A dramatic radiation of genera occurred in the deserts of North America. The tribe Nyctagineae and its subtribes are paraphyletic, due to over‐reliance on a few homoplasious characters, i.e., pollen morphology and involucre presence. Two notable characters associated with the desert radiation are cleistogamy and edaphic endemism on gypsum soils. We discuss evolutionary trends in these traits in light of available data about self‐incompatibility and gypsum tolerance in Nyctaginaceae.
Within‐population genetic structure and clonal diversity of a threatened endemic metallophyte, Viola calaminaria (Violaceae)
Authors: Bizoux Jean‐Philippe , Mahy Grégory
Published: February 2008

We studied the within‐population genetic structure and the clonality extent of Viola calaminaria, a rare endemic species of calamine soils, by means of RAPD markers in two populations (one recent and one ancient) with expected harsh and heterogeneous heavy‐metal stress. At a very local scale (0.2−3 m), clonal propagation was detected in both populations, but the levels of clonal diversity were high (number of genets/number of ramets sampled = 0.9 [recent] and 0.76 [ancient]) and the maximal observed extension of the clones was 0.4 m. This indicated that clonality is not, for the species, an important mode of propagation and that clonal growth cannot be interpreted as a strategy for propagating or perpetuating adapted genotypes under harsh ecological constraints. Spatial autocorrelations revealed a significant (P < 0.001) negative value of correlogram slope in the two populations even when a single individual per clone was considered (i.e., analysis at the genet level). We conclude that spatial genetic structure at a very local scale reflects limited gene flow due to restricted seed dispersal rather than variation in clonal pattern in response to environmental heterogeneity. At a larger scale (2–30 m), spatial autocorrelations revealed a positive (P < 0.001) correlation at < 3 m and a random pattern at larger distances for the two populations. This suggested a patchy distribution of the genetically linked individuals associated with a disrupted pattern at a longer distance probably due to gene flow by pollen dispersal and a seed bank effect. The implications for the conservation of V. calaminaria are discussed.
Self‐pollen interference is absent in wild radish (Raphanus raphanistrum, Brassicaceae), a species with sporophytic self‐incompatibility
Authors: Koelling Vanessa A. , Karoly Keith
Published: February 2008

Explaining the diversity of mating systems and floral forms in flowering plants is a long‐standing concern of evolutionary biologists. One topic of interest is the conditions under which self‐pollination can interfere with seed set for flowering plants with a self‐incompatibility system. We investigated the effect of self‐pollen interference for wild radish,Raphanus raphanistrum, which has sporophytic self‐incompatibility. We performed pollinations and determined seed set for plants grown in the greenhouse, using pollen mixtures representing either self‐ with outcross‐pollen or outcross‐pollen alone. Stigmas were collected for a subset of pollinated flowers to determine the number of pollen grains applied. Average seed set for the self/cross (5.13 seeds/pollination) and cross treatments (5.09 seeds/pollination) did not differ significantly. Stigmatic pollen loads averaged around 700 grains, an amount close to observed natural pollen loads onR. raphanistrum. We concluded that forR. raphanistrumin natural populations, self‐pollen is unlikely to interfere with outcross‐pollen success. This study is the first to investigate effects of self‐pollen interference on seed set for a homomorphic species with sporophytic self‐incompatibility where rejection occurs at the stigmatic surface.
Phylogeny and biogeography of the sandalwoods (Santalum, Santalaceae): repeated dispersals throughout the Pacific
Authors: Harbaugh Danica T. , Baldwin Bruce G.
Published: February 2008

Results of the first genus‐wide phylogenetic analysis for Santalum (Santalaceae), using a combination of 18S–26S nuclear ribosomal (ITS, ETS) and chloroplast (3′ trnK intron) DNA sequences, provide new perspectives on relationships and biogeographic patterns among the widespread and economically important sandalwoods. Congruent trees based on maximum parsimony, maximum likelihood, and Bayesian methods support an origin of Santalum in Australia and at least five putatively bird‐mediated, long‐distance dispersal events out of Australia, with two colonizations of Melanesia, two of the Hawaiian Islands, and one of the Juan Fernandez Islands. The phylogenetic data also provide the best available evidence for plant dispersal out of the Hawaiian Islands to the Bonin Islands and eastern Polynesia. Inability to reject rate constancy of Santalum ITS evolution and use of fossil‐based calibrations yielded estimates for timing of speciation and colonization events in the Pacific, with dates of 1.0–1.5 million yr ago (Ma) and 0.4–0.6 Ma for onset of diversification of the two Hawaiian lineages. The results indicate that the previously recognized sections Polynesica, Santalum, and Solenantha, the widespread Australian species S. lanceolatum, and the Hawaiian species S. freycinetianum are not monophyletic and need taxonomic revision, which is currently being pursued.
Genetic diversity and clonal vs. sexual reproduction in Fallopia spp. (Polygonaceae)
Authors: Grimsby Jonna L. , Tsirelson Dina , Gammon Melinda A. , Kesseli Rick
Published: February 2008

Although fundamental to the study of invasion mechanisms, the relationship between mode of reproduction and plant invasion is not well understood. Fallopia japonica (Japanese knotweed), a highly aggressive invasive plant in both Europe and North America, serves as a model species for examining this relationship. In Britain, F. japonica var. japonica is a single female clone reproducing solely through vegetative growth or obligate hybridization with other Fallopia spp. In the U.S., however, there is more evidence for sexual reproduction. Here, simple sequence repeat (SSR) markers were developed, and three Massachusetts populations were sampled at regular intervals. The amount of sexual and clonal reproduction in each population was determined based on within‐population genetic diversity. Clonal growth was apparent, but the populations together contained 26 genotypes and had evidence of sexual reproduction. One genotype that was present in all populations matched the single aggressive British clone of F. japonica var. japonica. Also, a potentially diagnostic marker for the F. sachalinensis genome provided evidence of inter‐ and intraspecific sexual reproduction and introgression. These differences observed in U.S. populations compared to European populations have significant implications for management of Fallopia spp. in the U.S. and underscore the importance of regional studies of invasive species.
Comparative infructescence morphology in Altingia (Altingiaceae) and discordance between morphological and molecular phylogenies
Authors: Ickert‐Bond Stefanie M. , Pigg Kathleen B. , Wen Jun
Published: February 2008

Altingia (Altingiaceae) is a tropical to subtropical Asian genus of lowland trees for which 5–15 species have been recognized. Morphological diversity, particularly of the mature infructescence, has been poorly known, especially for species with relatively localized and narrow distributions, and our understanding of Altingia has lagged behind that of its close temperate relative Liquidambar (sweet gum). In this contribution, mature infructescence structure, at the levels of anatomy, morphology, and micromorphology, and some distinctive inflorescence features, are described for five recognized species of Altingia, some for the first time. In the phylogenetic framework of both morphology and molecules, characters of Altingia contrast with those of Liquidambar and suggest that character evolution within Altingiaceae is at least partly related to geographic and climatic distribution. Differences in rates of evolution and morphological convergence suggest complex patterns of diversification in Altingiaceae at several different phylogenetic levels: (1) at the deep nodes, characters of the stem lineage fossil Microaltingia persist into crown group Altingiaceae, morphological stasis; (2) at the generic level, convergence within both Liquidambar and Altingia toward their respective habitats; (3) at the infrageneric level, morphological divergence in species diversification within Altingia, in response to diverse habitats of the eastern Asian subtropics; and (4) within the intercontinental disjunct species pair L. orientalis–L. styraciflua, morphological stasis.
Landscape structure, clonal propagation, and genetic diversity in Scandinavian populations of Arabidopsis lyrata (Brassicaceae)
Authors: Gaudeul Myriam , Stenøien Hans K. , Ågren Jon
Published: February 2008

Colonization history, landscape structure, and environmental conditions may influence patterns of neutral genetic variation because of their effects on gene flow and reproductive mode. We compared variation at microsatellite loci within and among 26 Arabidopsis lyrata populations in two disjunct areas of its distribution in northern Europe (Norway and Sweden). The two areas probably share a common colonization history but differ in size (Norwegian range markedly larger than Swedish range), landscape structure (mountains vs. coast), and habitat conditions likely to affect patterns of gene flow and opportunities for sexual reproduction. Within‐population genetic diversity was not related to latitude but was higher in Sweden than in Norway. Population differentiation was stronger among Norwegian than among Swedish populations (FST = 0.23 vs. FST = 0.18). The frequency of clonal propagation (proportion of identical multilocus genotypes) increased with decreasing population size, was higher in Norwegian than in Swedish populations, but was not related to altitude or substrate. Differences in genetic structure are discussed in relation to population characteristics and range size in the two areas. The results demonstrate that the possibility of clonal propagation should be considered when developing strategies for sampling and analyzing data in ecological and genetic studies of this emerging model species.
Pollen tube growth in association with a dry‐type stigmatic transmitting tissue and extragynoecial compitum in the basal angiosperm Kadsura longipedunculata (Schisandraceae)
Authors: Lyew Joelle , Li Ziru , Liang‐Chen Yuan , Yi‐bo Luo , Sage Tammy L.
Published: February 2008

Spatial features of pollen tube growth and the composition of the extracellular matrix (ECM) of transmitting tissue in carpels of Kadsura longipedunculata, a member of the basal angiosperm taxon Schisandraceae, were characterized to identify features of transmitting tissue that might have been important for pollen–carpel interactions during the early history of angiosperms. In addition to growing extracellularly along epidermal cells that make up stigmatic crests of individual carpels, pollen tubes grow on abaxial carpel epidermal cells between unfused carpels along an extragynoecial compitum to subsequently enter an adjacent carpel, a feature important for enhancing seed set in apocarpous species. Histo‐ and immunochemical data indicated that transmitting tissue ECM is not freely flowing as previously hypothesized. Rather, the ECM is similar to that of a dry‐type stigma whereby a cuticular boundary with associated esterase activity confines a matrix containing methyl‐esterified homogalacturonans. The Schisandraceae joins an increasing number of basal angiosperm taxa that have a transmitting tissue ECM similar to a dry‐type stigma, thereby challenging traditional views that the ancestral pollen tube pathway was similar to a wet‐type stigma covered with a freely flowing exudate. Dry‐type stigmas are posited to provide tighter control over pollen capture, retention, and germination than wet‐type stigmas.
Evolutionary correlations of polycyclic shoot growth in Acer (Sapindaceae)
Authors: Verdú Miguel , Climent José
Published: February 2008

Two strategies have evolved in understory trees in relation to light availability: maximization of light capture and shade tolerance. In the genus Acer, light capture is favored by a suite of traits maximizing twig thickness and leaf size and minimizing the density of branching in the crown. In contrast, shade tolerance is enhanced by minimizing crown area, crown volume, and total leaf area per unit height. Maples with polycyclic shoot growth (i.e., successive flushes of shoot growth separated by a resting phase within the same vegetative period) may benefit from the prolonged growth by growing more and increasing total leaf area; thus we hypothesize that polycyclism is evolutionarily correlated with the suite of traits related to light capture. We tested this hypothesis using different phylogenetic trees to explore correlations between polycyclism and both suites of traits. Polycyclism was correlated with the suite of traits maximizing light capture, suggesting that polycyclic maples are “optimists” (i.e., they make vigorous vertical extensions in rich light) and monocyclic maples are “pessimists” (i.e., they wait in the dark understory until a gap is opened). Both strategies have been described for different floras, and interestingly, polycyclic species recruit over a wider range of environments than the monocyclic species.
Inheritance of chloroplast DNA is not strictly maternal in Silene vulgaris (Caryophyllaceae): evidence from experimental crosses and natural populations
Authors: McCauley David E. , Sundby Allyson K. , Bailey Maia F. , Welch Mark E.
Published: February 2008

Chloroplast DNA (cpDNA) is maternally inherited in the majority, but not all, of angiosperm species. The mode of inheritance of cpDNA is a critical determinant of its molecular evolution and of its population genetic structure. Here, we present the results of investigations of the inheritance of cpDNA in Silene vulgaris, a plant used in a variety of studies in which cpDNA is an important component. PCR/RFLP markers were used to compare mother and offspring cpDNA genotypes sampled from two natural populations, and mother, father, and offspring genotypes obtained from controlled greenhouse crosses. Ten of 215 offspring cpDNA genotypes studied in the controlled crosses and three of 156 offspring from natural populations did not match that of the mother, demonstrating rare nonmaternal inheritance. That the chloroplast genome is occasionally transmitted through pollen is discussed in the context of using S. vulgaris cpDNA as a marker in studies of seed dispersal and when considering the joint evolution of the chloroplast and mitochondrial genomes.
Crassulacean acid metabolism photosynthesis in columnar cactus seedlings during ontogeny: the effect of light on nocturnal acidity accumulation and chlorophyll fluorescence
Authors: Hernández‐González Olivia , Villarreal Oscar Briones
Published: February 2008

Columnar cacti have been traditionally classified as crassulacean acid metabolism (CAM) plants, though recent research indicates some cactus seedlings employ the C3 pathway. To verify this last result, we measured acidity fluctuations for five columnar and one globular cactus species in seedlings from 1 to 48 d old after experimental exposure to 60% and 30% full sunlight, and in adult plants in the field. Using light‐response curves of chlorophyll fluorescence, we determined photosynthetic efficiency (ΔF/Fm′), maximum electron transport rate (ETRmax) and saturating photosynthetically active photon flux density (PPFDsat). All seedlings used the CAM pathway from their first day of development, and increases in nocturnal acidity depended on species, light treatment, and age. The CAM pathway was also found in adult plants. Cactus seedlings were able to acclimatize to light conditions by making photochemical adjustments, mainly by modifying the level of light at which photosystem II is saturated (PPFDsat). The presence of CAM in the seedlings of columnar cacti increases water‐use efficiency and reduces the risk of photoinhibition. This could favor survival in the highly variable light levels characteristic of the desert environments of columnar cacti.
Unisexual flower, spikelet, and inflorescence development in monoecious/dioecious Bouteloua dimorpha (Poaceae, Chloridoideae)
Authors: Kinney Michael S. , Columbus J. Travis , Friar Elizabeth A.
Published: February 2008

Unisexual flowers have evolved repeatedly in the angiosperms. In Poaceae, multiple transitions from bisexual to unisexual flowers are hypothesized. There appear to be at least three distinct developmental mechanisms for unisexual flower formation as found in members of three subfamilies (Ehrhartoideae, Panicoideae, Pharoideae). In this study, unisexual flower development is described for the first time in subfamily Chloridoideae, as exemplified by Bouteloua dimorpha. Scanning electron microscopy (SEM) and anatomy were used to characterize the development of male (staminate) and female (pistillate) flowers, spikelets, and inflorescences. We found the developmental pathway for staminate flowers in B. dimorpha to be distinct from that described in the other three subfamilies, showing gynoecial arrest occurs at a different stage with possible loss of some cellular contents. However, pistillate flowers of B. dimorpha had some similarity to those described in other unisexual‐flowered grasses, with filament and anther differentiation in abortive stamens. Comparing our findings with previous reports, unisexual flowers seem to have evolved independently in the four examined grass subfamilies. This analysis suggests the action of different genetic mechanisms, which are consistent with previous observations that floral unisexuality is a homoplasious condition in angiosperms.
Plastid movement in statocytes of the arg1 (altered response to gravity) mutant
Authors: Shiva Kumar Neela , Stevens Martin Henry H. , Kiss John Z.
Published: February 2008

The ability of a plant to respond to gravity is crucial for growth and development throughout the life cycle. A key player in the cellular mechanisms of gravitropism is ARG1 (altered response to gravity), a DnaJ‐like protein that associates with components of the vesicular trafficking pathway and carries a C‐terminal domain with similarities to cytoskeleton‐associated proteins. The arg1–2 mutant of Arabidopsis thaliana has reduced and delayed gravitropism in roots, shoots, and inflorescence stems when grown in the light or dark. We performed light microscopic studies of plastid movement in the gravity‐perceiving statocytes (endodermal cells) of hypocotyls of arg1–2 and WT light‐grown seedlings following reorientation to better characterize the role of ARG1 in gravitropism. Cryofixation/freeze substitution procedures were used because they provide a reliable indication of rapid cellular events within the statocytes. Our results suggest that ARG1 affects gravitropism by reducing plastid movement/sedimentation, a process known to be essential for early phases of signaling cascades in the statocytes.
AFLP markers as a tool to reconstruct complex relationships: A case study in Rosa (Rosaceae)
Authors: Koopman Wim J. M. , Wissemann Volker , De Cock Katrien , Van Huylenbroeck Johan , De Riek Jan , Sabatino Gerda J. H. , Visser Dirk , Vosman Ben , Ritz Christiane M. , Maes Bert , Werlemark Gun , Nybom Hilde , Debener Thomas , Linde Marcus , Smulders Marinus J. M.
Published: February 2008

The genus Rosa has a complex evolutionary history caused by several factors, often in conjunction: extensive hybridization, recent radiation, incomplete lineage sorting, and multiple events of polyploidy. We examined the applicability of AFLP markers for reconstructing (species) relationships in Rosa, using UPGMA clustering, Wagner parsimony, and Bayesian inference. All trees were well resolved, but many of the deeper branches were weakly supported. The cluster analysis showed that the rose cultivars can be separated into a European and an Oriental cluster, each being related to different wild species. The phylogenetic analyses showed that (1) two of the four subgenera (Hulthemia and Platyrhodon) do not deserve subgeneric status; (2) section Carolinae should be merged with sect. Cinnamomeae; (3) subsection Rubigineae is a monophyletic group within sect. Caninae, making sect. Caninae paraphyletic; and (4) there is little support for the distinction of the five other subsections within sect. Caninae. Comparison of the trees with morphological classifications and with previous molecular studies showed that all methods yielded reliable trees. Bayesian inference proved to be a useful alternative to parsimony analysis of AFLP data. Because of their genome‐wide sampling, AFLPs are the markers of choice to reconstruct (species) relationships in evolutionary complex groups.
Student Employment During the Transition to College in the United States
Authors: Bozick Robert
Published: February 2008

In this paper, I use a nationally representative sample of American high school seniors in 1992 to examine change and stability in the employment patterns of youth as they make the transition from high school to college. Students with weak attachments to the labor force in high school tend to remain unemployed during the first year of college. Conversely, students who work in moderation while in high school have the highest odds of enrolling in college and working while doing so. Compared with their nonworking peers, student workers enter college with lower grades and test scores but are equally engaged in school. Socioeconomic factors have little bearing on high school employment, but they are strongly related to postsecondary employment: students who work during the first year of college have fewer socioeconomic resources than nonworking students. The findings highlight the intersection of school and work in young adulthood and its importance when studying the transition from high school to college among contemporary American youth.
Inside Front Cover: Mobility and Dynamics of Charge Carriers in Rubrene Single Crystals Studied by Flash‐Photolysis Microwave Conductivity and Optical Spectroscopy (Adv. Mater. 5/2008)
Authors: Saeki A. , Seki S. , Takenobu T. , Iwasa Y. , Tagawa S.
Published: February 2008

Electrodeless photoconductivity measurements of a rubrene single crystal are performed by microwave conductivity and transient optical spectroscopy, demonstrating anisotropy and ambipolarity. From these comprehensive studies, Akinori Saeki, Seiichi Tagawa, and co‐workers discuss on p. 920 the optoelectronic properties of rubrene single crystal in terms of charge recombination of holes and electrons, exciton–exciton annihilation, quantum efficiency of charge carrier generation, triplet contribution, and the extinction coefficients of ionic species accessed by pulse radiolysis.
Explaining the enhanced performance of pulsed bioreactors by mechanistic modeling
Authors: Franco Amaya , García Carlos , Carrasco Eugenio F. , Roca Enrique
Published: February 2008

In this work, steady‐state mass balance based models were applied to two UASB reactors and three UAF for a better understanding of the role of pulsation on the efficacy improvement. Models were defined taking into account the hydraulic behavior of each digester and the limiting mechanism of the overall process kinetics (mass transfer or biochemical reaction rate). The application of the model allows to identify that mass transfer was the controlling step in all the reactors, except for the nonpulsed UASB, where methanogenic activity controlled the reactor performance in the last operation steady states. Mass transfer coefficients were higher for pulsed reactors and, in general, a good agreement between those estimated by an empirical correlation and from the model was obtained. Damköhler number values supported that the external mass transfer resistance was not negligible with respect to the process kinetic and in addition, in most cases, it controls the overall process in the reactors. The relative importance of external and internal mass transfer rate was calculated through the Biot number. The values of this dimensionless module indicated that external transport was the main contributor to overall mass transfer resistance. © 2008 American Institute of Chemical Engineers AIChE J, 2008
Dynamics of particles suspended in a yield stress fluid flowing in a pipe
Authors: Merkak Othmane , Jossic Laurent , Magnin Albert
Published: February 2008

This study seeks to understand the basic mechanisms governing the dynamics of a solid particle in a Poiseuille flow field of a viscoplastic fluid. An experimental set‐up to create flows with a prescribed flow rate and enable the particles to be visualized in three dimensions was designed and validated. The absence of slip at the interfaces between flows and particles was characterized. The Reynolds numbers are low, gravity effects negligible and plastic effects significant. The ratio of pipe diameter to particle diameter is 8. The dynamics of a particle in a velocity field depends strongly on its position in the sheared wall zone or in the moving rigid zone. The effect of rigid and sheared zones on particle behavior was examined. Changes in particle translation and rotation velocities were quantified. © 2008 American Institute of Chemical Engineers AIChE J, 2008
Übertragung und Amplifikation von Informationen und Eigenschaften in nanostrukturierten Flüssigkristallen
Authors: Goodby John W. , Saez Isabel M. , Cowling Stephen J. , Görtz Verena , Draper Michael , Hall Alan W. , Sia Susan , Cosquer Guirac , Lee Seung‐Eun , Raynes E. Peter
Published: February 2008

In den letzten Jahren hat sich das Design der chemischen Strukturen flüssigkristalliner Materialien stark und in vielen Fällen sogar radikal verändert. Seit Reinitzers Tagen wurden Flüssigkristalle entweder als stab‐ oder als scheibenförmig klassifiziert; Kombinationen davon führten zu phasmidischen Flüssigkristallen. Die Entdeckung, dass Materialien mit gebogenen Molekülstrukturen eine völlig neue Familie von Mesophasen bilden, hat den Fokus auf Substanzen mit einer großen Variationsbreite an Molekültopologien gerichtet: von Pyramiden zu Kreuzen und dendritischen Molekülen. Die Molekülstrukuren supermolekularer Materialien können durch Konformationsänderungen verformt werden können, was zu einer Stabilisierung der Mesophase führen kann, und Substanzen, die selbst nicht mesogen sind, können mesogene supramolekulare Komplexe bilden. Die Bildung von Mesophasen ist ein Prozess der Selbstorganisation, der bei supramolekularen Systemen auf zwei Ebenen stattfindet.

In der englischen Fassung wird der Begriff “self‐assembly” (ins Deutsche ungefähr übersetzbar mit “Assoziation”) für den Aufbau supramolekularer Strukturen durch intermolekulare Wechselwirkungen verschiedener Art, z. B. Wasserstoffbrücken, verwendet. Der Begriff “self‐organization” (Selbstorganisation) dagegen bezieht sich in der englischen Fassung ausschließlich auf die unspezifischen Wechselwirkungen, die mit der Bildung von flüssigkristallinen Phasen aus mesogenen Einheiten (molekular, supramolekular oder supermolekular) verknüpft sind. In der deutschen Fassung wird der Begriff “Selbstorganisation” jedoch zur Beschreibung beider Prozesse verwendet.

In diesem Aufsatz wird gezeigt, dass 1) verformbare Molekülstrukturen und ‐topologien supermolekularer und selbstorganisierter supramolekularer Systeme, 2) Erkennungsprozesse an Grenzflächen von Superstrukturen und 3) die Übertragung und Amplifikation dieser Strukturen zur Bildung ungewöhnlicher Mesophasen führen können, die mit der konventionellen Kontinuumstheorie nicht ausreichend beschrieben werden können.
Radiation induced graft copolymerization of vinyl monomers and their binary mixture onto rayon fibre
Authors: Rattan Sunita , Maitra Jaya , Misra B. N. , Kaur Inderjeet
Published: February 2008

Ethyl acrylate (EA), Vinyl imidazole (VI), and their binary mixture have been copolymerized onto rayon in aqueous medium by mutual method using γ‐radiation. The graft yield has been determined as a function of different reaction parameters such as total dose, concentration of vinyl monomers, and amount of water. Effect of surfactant (1‐octane sulfonic acid, sodium salt) has been studied on the percentage of grafting of EA, VI, and (EA + VI). A plausible mechanism has been suggested to explain the observed behavior of the surfactant on grafting. Water retention and moisture regain of the grafted film was determined at appropriate relative humidity. The graft copolymers have been characterized by IR spectroscopy and scanning electron microscopic methods. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008