bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptations of plants to burial in coastal sand dunes
Authors: Maun M A
Published: April 2011

One of the most obvious features on the foredunes and strands of coasts and lakes is recurrent burial in sand. Burial levels vary in different coastal sand dune systems and influence the physical and biotic microenvironment of the plant and soil. Foredune plants along coasts possess numerous adaptations to withstand burial. Studies show that below a certain threshold level of burial, the growth of all foredune plant species is stimulated probably because of multiple factors, namely improved soil resources, increase in soil volume, reactive plant growth, and enhanced mycorrhizal activity. However, as the level of burial increases, the positive response starts to decline until it becomes a negative value. For example, burial may reduce seed germination, seedling emergence, survival, and growth of seedlings and adult plants. At the community level, burial acts as a filter and selectively eliminates susceptible species, reduces the relative abundance of less tolerant species, and increases the abundance of tolerant and sand-dependent species. However, if sand deposition continues unabated, even the sand-dependent species are eliminated and a bare area is created. The emergence of a plant from a burial deposit primarily depends on the energy reserves in its storage organs and the speed, depth, and frequency of burial. Upon burial the plants shift resources from the belowground to the aboveground parts. Different plants show varied morphological responses to sand accretion. For example, the culms of grasses emerge by an increase in the number of nodes per culm and the elongation of internodes. Similarly, the emergent trunks and woody branches of tolerant trees and shrubs produce new buds and suckers at a higher level on the stem. In response to burial, the coastal sand dune species produce shootborne roots close to the new soil surface probably because of decreased oxygen levels.Key words: sand accretion, adaptations to burial, zonation of vegetation, burial of seeds, plant vigour, impact on communities, modes of emergence.
Catalytic exchange of 18O from 13C18O-labelled CO2 by wild-type cells and ecaA, ecaB, and ccaA mutants of the cyanobacteria Synechococcus PCC7942 and Synechocystis PCC6803
Authors: So Anthony KC , Van Spall Harriette GC , Coleman John R , Espie George S
Published: April 2011

Expression constructs carrying the ecaA, ecaB, and ccaA genes from the cyanobacteria Synechococcus PCC7942 and Synechocystis PCC6803 were generated and each transformed into Escherichia coli. Lysates from cells expressing recombinant protein were prepared and assayed using mass spectrometry for their ability to catalyze the exchange of 18O from 13C18O to H2O. No carbonic anhydrase (CA) activity was detected from the cell lysates containing recombinant EcaA or EcaB proteins, whereas the lysate harbouring the CcaA polypeptide clearly accelerated the rate of 18O exchange. An ecaA deletion mutant in Synechococcus and insertionally inactivated ecaB and ccaA mutants in Synechocystis were generated and similarly assessed for CA activity. All mutants displayed a transient, ethoxyzolamide-sensitive, CA-like catalysis that was also exhibited by wild-type cells. The CcaA-deficient mutant showed a reduced capacity to exchange 18O out of 13C18O-labelled CO2 in the light as well as an absolute requirement for high Ci for growth, reflecting the importance of the carboxysomal CA to the operation of the cyanobacterial CO2-concentrating mechanism. No detectable differences in 18O exchange patterns, CO2 or HCO3- transport, or steady-state growth were observed between the ecaA and ecaB mutants and wild-type cells, indicating that neither EcaA nor EcaB play an essential catalytic role in the functioning of the CO2-concentrating mechanism.Key words: carbonic anhydrase, CO2-concentrating mechanism, cyanobacteria, 18O exchange, Synechococcus PCC7942, Synechocystis PCC6803.
Acid secretion, calcification, and photosynthetic carbon concentrating mechanisms
Authors: McConnaughey Ted
Published: April 2011

Bicarbonate-based photosynthesis requires equal numbers of proton equivalents. Aquatic plants and photosynthetic symbioses can scavenge protons from ambient solutions, or they can manufacture protons through calcification. Both mechanisms are widely employed. This review examines how aquatic photoautotrophs couple calcification to photosynthesis, and the advantages and limitations of this physiology.Key words: calcification, calcium, carbonate, bicarbonate, photosynthesis, aquatic.
The role of the chloroplast in inorganic carbon uptake by eukaryotic algae
Authors: Moroney James V , Chen Zhi-Yuan
Published: April 2011

The role of the chloroplast in the adaptation to low CO2by eukaryotic algae is reviewed. Eukaryotic algae can grow on very low CO2levels because of the presence of a CO2concentrating mechanism (CCM). This review is focused on the localization of key photosynthetic enzymes such as ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) and carbonic anhydrase as well as the location of presumptive components of the CCM and photorespiratory cycle within the chloroplast. Previous immunolocalization studies place as much as 99% or as little as 5% of the cell's Rubisco in the chloroplast pyrenoid. These different results are summarized, and an alternative explanation is provided. The different results appear to be due to the growth regime of the algae as well as differences in quantitation. Evidence suggests that a large majority of Rubisco is located within the pyrenoid. We have also summarized the recent discovery of a thylakoid-bound carbonic anhydrase that is essential to growth on low CO2. A model depicting a possible role for this carbonic anhydrase in photosynthesis is presented.Key words: chloroplast, algae, pyrenoid, carbonic anhydrase, photosynthesis.
Notes onTremella mesentericaand allied species
Authors: Bandoni R , Ginns J
Published: April 2011

Some aspects of development and biology of Tremella mesenterica and two closely allied species are discussed; some associated fungi are noted. Tremella brasiliensis, previously known only from neotropical areas, is reported from Japan; an extended description is provided. One North American species, Tremella mesenterella Bandoni & Ginns, is described as new, and other taxa with superficially similar basidiocarps are discussed.Key words: Tremellaceae, Tremella, T. mesenterica, T. mesenterella, T. philippinensis, T. rufobrunnea, conidium ontogeny, basidiome development.
Performance of Pinus contorta inoculated with two strains of root endophytic fungus, Phialocephala fortinii: effects of synthesis system and glucose concentration
Authors: Jumpponen Ari , Trappe James M
Published: April 2011

Melanized, root-colonizing fungi are ubiquitous. Their ecological role, however, is poorly understood, and results of studies of associations between these fungi and their potential host plants are controversial. The culture system under which the association is studied may also affect the host-fungus interaction. Two experiments on the association between Pinus contorta Dougl. ex Loud., and a root-inhabiting endophytic fungus, Phialocephala fortinii Wang & Wilcox, were conducted to study the host response to inoculation. First, Pinus contorta seedlings were inoculated with two strains of Phialocephala fortinii and grown under aseptic conditions with five levels of glucose in the medium. Multiple linear regression analysis was employed to study the effects of inoculation and glucose concentration. Second, the same two strains of Phialocephala fortinii were inoculated on Pinus contorta seedlings in open pot cultures. Inoculation resulted in substantial increase in all biomass components of the host plant in the aseptic culture system. Total biomass, for example, was increased approximately 60 and 90% when seedlings were inoculated with strain 1 and strain 2, respectively. No seedling mortality was observed following fungal inoculation after 6 months of incubation. Inoculation increased host biomass with increasing glucose concentration, while glucose concentration did not significantly affect host biomass when no inoculum was added. Inoculation lowered foliar nitrogen and phosphorus concentrations. The effect of glucose concentration on the foliar nutrient concentrations varied between the two strains. In the open pot cultures, inoculation did not affect biomass or foliar nutrient concentration. We hypothesise that the observed increases in host growth in the aseptic culture system are due to fungal respiration in a closed culture system, the carbohydrates made available to the host plant by the fungus, or, most likely, to a combination of both factors. The ecological role of Phialocephala fortinii and the validity of aseptic culture assays are discussed.Key words: dark-septate endophytes, deuteromycetes, fungi, host-fungus associations, root endophytes, symbiosis.
Developmental aspects of tristyly in Lythrum salicaria
Authors: Mal Tarun K
Published: April 2011

The developmental basis of floral polymorphism was investigated in the tristylous invasive species, Lythrum salicaria L. (Lythraceae). In tristylous species, the stigmas are positioned above (in the long morph), below (in the short morph), or between (in the mid morph) the outer and inner staminal whorls. Flower samples were collected at three different growth stages (early, pre-anthesis, and post-anthesis) from three genotypes from each of the three morphs to observe morph-specific differences in growth patterns of filaments and styles and their constituent epidermal cells. From each flower, I measured the length of styles and two types of stamens and their epidermal cells at the basal, intermediate, and apical regions of each organ. Differentiation of organ levels begins at a very early stage. Growth rate of the long pistil is higher than in the mid pistil followed by the short pistil. However, the growth rate of epidermal cells is higher in the short style followed by the mid and long styles. The number of cells does not increase during style development in the short morph but does increase in the long and mid morphs. Although the relative growth of the outer stamens is greater than in the inner stamens in all three morphs, the relative cell size is greater in the inner stamens than in the outer stamens. Cell size differs between outer and inner stamens in the long and mid morphs but not in the short morph. The intermediate cells are larger compared with the basal and apical cells of the stamens and styles. The number of epidermal cells increases in the outer stamens during development, whereas it remains constant in the inner stamens of the mid morph and increases only slightly in the inner stamens of long morph.Key words: floral development, growth and division of epidermal cells, heterostyly, purple loosestrife, style and stamen growth, style-stamen polymorphism.
Regulation of ethylene production and ripening by saskatoon (Amelanchier alnifolia Nutt.) fruit
Authors: Rogiers Suzy Y , Kumar GN Mohan , Knowles N Richard
Published: April 2011

Changes in respiration and ethylene production were characterized during maturation and ripening of saskatoon (Amelanchier alnifolia Nutt.) fruit. On a per fruit basis, respiration and ethylene production increased 78 and 400%, respectively, as fruit ripened on the plant and trends were consistent with those for climacteric fruits. When estimated on a fresh and dry weight basis, increased rates of ethylene production were still apparent during ripening; however, respiration rate declined. Trends in respiration rates and endogenous ethylene levels of harvested fruit of nine maturity classes, from immature green (class one) to fully ripe and purple (class nine), were consistent with those of fruit growing on the plant. Tissue prints showed that ACC (1-aminocyclopropane-1-carboxylic acid) oxidase was distributed throughout the pericarp of fruit at all nine maturity stages and that the enzyme was most concentrated in the immature stages on a per fruit basis. On a protein basis, ACC oxidase increased progressively with development of cv. Smoky fruit but remained relatively constant over the nine maturity classes of cv. Northline fruit. In contrast, ACC oxidase levels were relatively low in cv. Pembina fruit over the first four maturity classes, increased substantially as fruits developed from class four to five, then remained constant as fruit ripened to maturity class nine. Treating immature harvested Pembina fruit (maturity classes one to three) with ACC effected a 28- to 108-fold increase in ethylene production, compared with an average of only 7-fold for ACC-treated fruit of maturity classes four through nine. Preharvest treatment of class-three fruit with ACC induced ripening to maturity class eight within 5 days, while untreated fruit required 15 days to reach class eight. Vacuum infiltrating class four fruit with alpha-aminooxyacetic acid (AOA) or aminoethoxyvinyl glycine (AVG) inhibited ethylene production and color development substantially. The inhibiting effect of AOA on ripening was eliminated when fruit were infiltrated with equimolar concentrations of AOA and ACC. Cobalt, an ACC oxidase inhibitor, also inhibited ethylene production and ripening. Collectively, our results indicate that ethylene synthesis by preclimacteric fruit is limited by the availability of ACC, ethylene is responsible for initiating ripening, and thus, saskatoon fruit are climacteric.Key words: Amelanchier alnifolia, saskatoon, fruit ripening, ethylene.
Studies of conidial anatomy and conidiogenesis in Sporoschisma nigroseptatum using light and electron microscopy
Authors: Ho Wai-Hong , Goh Teik-Khiang , Hyde Kevin D , Hodgkiss I John
Published: April 2011

The results of an ultrastructural study of the conidial anatomy and conidiogenesis in Sporoschisma nigroseptatum are presented. The development of the conidial chain involves endogenous conidial ontogeny, apical wall-building, and retrogressive conidial delimitation followed by cessation of apical wall-building, then replacement ring wall-building of additional retrogressively delimited conidia, and extrusion of the true conidial chain through the terminal aperture of the conidiogenous cell. Maturation of conidia involves deposition of two inner wall layers and formation of five distosepta. Conidial chains secede schizolytically. No proliferation of the conidiogenous cell occurs and the conidium is delimited by a cross wall that is discontinuous with the periclinal wall. Each conidium has polar plug-and-socket-like structures that are interlocked between adjacent conidia along the conidial chain. Similar plug-and-socket-like structures are also seen in other Sporoschisma species. The taxonomy of Chalara is also briefly discussed with reference to patterns of conidial wall-building.Key words: Chalara, conidial chain, conidial ontogeny, ultrastructures.
Why does the flower of Lonicera japonica open at dusk?
Authors: Miyake Takashi , Yahara Tetsukazu
Published: April 2011

We investigated contributions of diurnal pollinators and a nocturnal pollinator to pollen transfer in Lonicera japonica (Caprifoliaceae), whose flowers have traits typical of the hawkmoth-pollination syndrome. Diurnal bees, Tetralonia nipponensis and Lasioglossum sp., delivered more pollen grains than the nocturnal hawkmoth Theretra japonica per visit, suggesting that these bees were also effective pollinators. However, these bees removed over 10 times more pollen at one visit than the hawkmoth. Because of the higher pollen consumption by these bees, anthesis at dusk is considered to be optimal for Lonicera japonica to maximize overall pollen transfer under the visitation of both nocturnal and diurnal pollinators. Tetralonia japonica dispersed color dye farther than the other pollinators, which suggests that the nocturnal pollinator contributes more to cross-pollination than the diurnal pollinators.Key words: Lonicera japonica, hawkmoth-pollinated flowers, pollinator efficiency, pollen removal, pollination syndromes, timing of anthesis.
Habitat and temporal differences among soil microfungal assemblages in Ontario
Authors: Keller Linette , Bidochka Michael J
Published: April 2011

A survey of the soil microfungi in the A horizons of soils taken from four sites (deciduous forest, cedar forest, old field, and alfalfa field) in Central Ontario at three times (May, June, and August) in one year was conducted to determine habitat and temporal differences of fungal assemblages. Approximately 70 species of fungi were identified. In all habitats, species in the genera Penicillium, Acremonium, Talaromyces, Cladosporium, Cunninghamella, and Paecilomyces were isolated most frequently. Cedar forest soils showed the lowest species turnover with time, and Aspergillus fumigatus (Fres.) was consistently one of the most abundant species throughout the sampling period. Total fungal abundance increased over the sampling period in cedar forest soils, a trend not observed in deciduous forest soils. Fungal abundance, as well as the total number of species, in soils from the alfalfa field and old field sites decreased in August. Narrow-amplitude, broad-amplitude, and occasional species were characterized. Results are discussed with reference to the biotic and abiotic factors that may influence fungal occurrence and abundance.Key words: fungal soil ecology, microfungi, Ontario, fungal species composition.
Molecular phylogenetic studies in the genus Amanita
Authors: Weiß Michael , Yang Zhu-Liang , Oberwinkler Franz
Published: April 2011

A group of 49 Amanita species that had been thoroughly examined morphologically and anatomically was analyzed by DNA sequence comparison to estimate natural groups and phylogenetic relationships within the genus. Nuclear DNA sequences coding for a part of the ribosomal large subunit were determined and evaluated using neighbor-joining with bootstrap analysis, parsimony analysis, conditional clustering, and maximum likelihood methods. Sections Amanita, Caesarea, Vaginatae, Validae, Phalloideae, and Amidella were substantially confirmed as monophyletic groups, while the monophyly of section Lepidella remained unclear. Branching topologies between and within sections could also partially be derived. Subgenera Amanita and Lepidella were not supported. The Mappae group was included in section Validae. Grouping hypotheses obtained by DNA analyses are discussed in relation to the distribution of morphological and anatomical characters in the studied species.Key words: fungi, basidiomycetes phylogeny, Agaricales, Amanita systematics, large subunit rDNA, 28S.
Localization of oleosomes in the root nodules of alfalfa (Medicago sativa)
Authors: Martin A Darryl , Bal Arya K , McKenzie David B
Published: April 2011

Histological studies of rhizobia-induced nodules and spontaneous pseudonodules of alfalfa were undertaken to reveal the distribution pattern of oleosomes. Alfalfa (Medicago sativa L. cv. 'Algonquin') seedlings were inoculated with Rhizobium meliloti (strain Balsac), and grown in controlled conditions. Seedlings were also grown aseptically to obtain spontaneous pseudonodules. Nodule slices were fixed in a paraformaldehyde-glutaraldehyde mixture and processed for embedding in Spurr's medium after OsO4 treatment and en bloc staining, with p-phenylenediamine (pPD) in 70% ethanol, for oleosomes. As a control, hexane extraction of lipids was employed. In pseudonodules, oleosomes were present in the vascular parenchyma, the meristem region and in the five to seven layers of cortical cells adjacent to the vascular tissue. The allocation of energy stored as triacylglycerides, in the form of oleosomes, and starch indicates that pseudonodules are a sink for carbon, possibly functioning as storage organs. In mature nodules, oleosomes were distinguished clearly in nodule parenchyma but were absent in infected cells. Young nodules were devoid of oleosomes. The prevalence of oleosomes in the mature nodules may indicate that the triacylglycerides are stored for overwintering, as alfalfa nodules are known to be perennial. The oleosomes in root nodules of alfalfa do not appear to be directly associated with nitrogen fixation per se.Key words: oleosomes, root nodules, Medicago sativa, Rhizobium, pseudonodules.
Fruticose arboreal lichen biomass accumulation in an old-growth balsam fir forest
Authors: Arseneau Marie-Josée , Ouellet Jean-Pierre , Sirois Luc
Published: April 2011

The standing biomass accumulation of lichens from the genera Alectoria, Bryoria, and Usnea was studied along two environmental gradients, altitude and height along the vertical tree axis, in an old-growth balsam fir (Abies balsamea (L.) Mill.) forest. Lichens were sampled from 50 trees in five sampling sites at an altitude of 720-1068 m asl and encompassing three vegetation belts (mountain, subalpine, and alpine). The lichen biomass accumulation rate was studied at branch and tree levels. The Gompertz equation was used to assess the relationship between time since lichen colonization and standing lichen biomass. The relationship between tree lichen biomass and age was not significant. Colonization delay was assumed to correspond to the age of the youngest branch supporting a given lichen taxon, and our results show that it increased from mountain to alpine belts. Variations in lichen accumulation were related to the branch position along the tree height and altitude. Lichen biomass accumulation rates decreased from tree top to base. We speculate that this reduction reflects a response to microclimatic gradients, aging of thalli, fragmentation, competition, succession, and caribou grazing. The accumulation rate was greater in the mountain belt (r = 0.063) than in the alpine belt (r = 0.027). In the subalpine belt, the relationship between lichen biomass and time was not significant (p > 0.05). The decrease in accumulation rate along the altitudinal gradient may be primarily explained by climatic conditions.Key words: arboreal lichens, lichen biomass accumulation, altitude effect, height in tree effect, Alectoria, Bryoria, Usnea.
Introduction to the red-fruited hawthorns (Crataegus, Rosaceae) of western North America
Authors: Phipps J B
Published: April 2011

Howell's failure in 1898 to typify Crataegus columbiana Howell (the species is based on noncited discordant paratype elements) and the readiness of later authors to make new varieties in this species without resolving the type problem has been the cause of much confusion in the nomenclature of the western red-fruited hawthorns. This has been increased by the failure to recognize Crataegus williamsii Eggl. and compounded by almost a century of no revisionary study on western Crataegus with the further result that boundaries between taxa have been routinely misunderstood outside Colorado. In pursuit of a solution doing least violence to conventional usage I have lectotypified C. columbiana and resuscitated Crataegus piperi Britton (in a recent paper), realigned C. piperi as Crataegus chrysocarpa var. piperi (Britton) Eggl. and resurrected C. williamsii. There are thus five established native western species of red-fruited hawthorns, the above two, and Crataegus wootoniana Eggl., Crataegus macracantha Lodd. ex Loud. and Crataegus erythropoda Ashe in addition to the introduced Crataegus monogyna Jacq., all of which have been recognized as occurring at least somewhere in this region for many decades. This paper also adds the first authenticated record for wild Crataegus laevigata (Poir.) DC. in North America. Separation of the two varieties of C. chrysocarpa is validated by numerical taxonomy. The taxa concerned are illustrated with line drawings and provided with detailed range maps. Colour photographs illustrate typical habitat types and show the development of fruit colour.Key words: systematics, Crataegus, Rosaceae, red-fruited, western North America.
A key to identify perennial grasses in central Argentina based on microhistological characteristics
Authors: Lindström Lilia I , Mújica María B , Bóo Roberto M
Published: April 2011

The most important economic activity on the Caldenal rangelands in central Argentina is cattle raising in cow-calf operations. It is known that grasses are the bulk of the diets and a previous study provided detailed information on the epidermal structures of the most important grass species in the region. The objective of this work was the elaboration of a key to facilitate the microhistological analysis of esophageal, fecal, and ruminal samples. The key allows for the identification of eleven perennial grass species from epidermal characteristics of the blades, sheaths, and stems. The most important epidermal characteristics relevant to microhistological identification are illustrated for each species.Key words: leaf and stem epidermis, Gramineae, microhistological key, perennial grasses, Caldenal.
Response of microbial processes and fungal community structure to vegetation management in mixedwood forest soils
Authors: Houston APC , Visser S , Lautenschlager R A
Published: April 2011

Previous research to determine the impacts of harvesting and site preparation on microbial processes and decomposer fungi in mixedwood forests indicated that effects were minimal. As an extension to this research, the present study was conducted to evaluate if microbial processes and decomposer fungi were sensitive to manual or chemical vegetation management in addition to harvesting and site preparation. The impact of vegetation management on microbial processes and decomposer fungi was examined in organic and mineral soil from harvested sites in northwestern Ontario. Three vegetation management treatments were applied to three clear-cut and prepared sites 2 years prior to the initiation of the study. Four treatments were established within each site: (i) harvested (control), (ii) glyphosate herbicide (Vision®), (iii) triclopyr herbicide (Release®), and (iv) manually operated brushsaws. The objective of the study was to determine the response of basal respiration, microbial biomass C, metabolic quotients (qCO2), microbial carbon : soil organic carbon ratio (Cmic/Corg), nitrogen mineralization, and fungal community structure to vegetation management by chemical and manual means. Relative to the harvested control, vegetation management had no significant impact on fungal community structure as evidenced through rank abundance curves and indices of fungal community richness, diversity, evenness, or dominance. Although the abundances of the majority of fungal species were not impacted by vegetation management, herbicide and brushsaw use decreased the isolation frequencies of Mortierella vinacea (Dixon-Stewart) and Paecilomyces carneus (Duché and Heim) Brown and Smith, respectively. Occurrence of Paecilomyces carneus was significantly greater in the organic soil than in the mineral soil of the harvested control, but this difference was not detectable in the blocks that had undergone vegetation management. Two years after vegetation management was imposed there were no detectable effects on basal respiration, microbial biomass C, qCO2, Cmic/Corg, or nitrogen mineralization in either the organic or mineral soil layers as compared with measurements made in the harvested control plots.Key words: harvesting, herbicide, brushsaw, fungal community, microbial processes.
Effectiveness of Glomus species in protecting white clover against nematode damage
Authors: Habte M , Zhang Y C , Schmitt D P
Published: April 2011

Three species of arbuscular mycorrhizal (AM) fungi, Glomus aggregatum Schenck and Smith emend. Koske, Glomus intraradices Schenck and Smith, and Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe, were evaluated for their effectiveness to suppress the plant parasitic nematode Meloidogyne incognita (Kofoid and White) Chitwood in white clover (Trifolium repens L.) in a greenhouse study. Forty 1-day-old seedlings not colonized or colonized to the same extent by the fungi were transplanted into a growth medium uninoculated or inoculated with 10 000 M. incognita eggs. After 40 days of further growth, root mass, shoot mass, extent of galling, number of nematodes and nematode eggs in roots, and extent of mycorrhizal colonization of roots were determined. Growth of white clover was significantly stimulated by mycorrhizal colonization, and nematodes caused the greatest damage when plants were not colonized by the fungi. The degree to which mycorrhizal fungi reduced nematode damage varied with the species of mycorrhizal fungus; the extent of damage reduction ranged from 19 to 49.8%, based on loss of shoot mass. The effectiveness of the mycorrhizal fungal species in suppressing nematodes was not related to the degree to which they colonized roots or their effectiveness in enhancing host growth.Key words: AM colonization, galls, Glomus aggregatum, Glomus intraradices, Glomus mosseae, inoculum potential, Meloidogyne incognita, nematode eggs, phosphorus.
Lignin distribution in mild compression wood of Pinus radiata
Authors: Donaldson Lloyd A , Singh Adya P , Yoshinaga Arata , Takabe Keiji
Published: April 2011

Lignin distribution in the tracheid cell wall of mild compression wood in Pinus radiata D. Don was examined by interference microscopy, confocal fluorescence microscopy, and ultraviolet (UV) microscopy. Two anatomically different samples of mild compression wood were compared with a sample of normal wood using quantitative interference microscopy and microdensitometry combined with confocal fluorescence microscopy to estimate the quantitative or semiquantitative lignin distribution in the S2 and S2L regions of the secondary cell wall and of the cell corner middle lamella (CCML). One of these samples was briefly examined by UV microscopy for comparison. Quantitative interference microscopy provided information on lignin concentration in different regions of the cell wall with values of 26, 46, and 57%, respectively, for the S2, S2L, and CCML regions of sample 1 and 20, 29, and 46%, respectively, for the same regions of sample 2. Microdensitometry of confocal fluorescence images provided semiquantitative information on the relative lignin distribution based on lignin autofluorescence. Comparison between the two compression wood samples using autofluorescence gave results that were in partial agreement with interference microscopy with respect to the relative lignification levels in the S2, S2L, and CCML regions. Some improvement was achieved by using calibration values for hemicellulose rather than holocellulose for interference data in the S2L region. Results for UV microscopy performed on sample 1 indicated that the lignification of the CCML region was comparable with that of the S2L region in this sample but with some variation among cells. All three techniques indicated significant variation in lignification levels of the S2L and CCML regions among adjacent cells and a significant reduction in the lignification of the CCML region compared to normal wood.Key words: lignin distribution, interference microscopy; confocal fluorescence microscopy, UV microscopy, mild compression wood, Pinus radiata D. Don.
Cernes manquants et houppier vivant chez le pin laricio (Pinus nigra Arn. ssp. laricio (Poir.) Maire)
Authors: Meredieu Céline , Caraglio Yves
Published: April 2011

During a study on the live crown characteristics of Pinus laricio (Pinus nigra Arn. ssp. laricio (Poir.) Maire), the observation of branch cross-sections allowed us to work on the problem of the discontinuance of cambial activity. This work points out the existence of missing rings with a histologic point of view and establishes the generality of the phenomenon for this species. In addition to the observations at the base of living branches, the cross-sections in all the successive growth units of the branch were observed to establish the distribution of the annual wood layers along the branch and to ascertain the dissymmetry between the upper side and the lower side of the branch. The occurrence of this phenomenon in the upper part of the crown raises the problem of the contribution of these branches to tree development and its implication in forest management.Key words: growth rings, Pinus nigra Arn. ssp. laricio (Poir.) Maire, missing rings, anatomy, branch growth, crown.
Virulence dynamics, phenotypic diversity, and virulence complexity in two populations of Puccinia triticina in Canada from 1987 to 1997
Authors: Kolmer J A
Published: April 2011

Populations of Puccinia triticina (causal agent of wheat leaf rust) in Ontario, Quebec, Manitoba, and Saskatchewan were analysed for frequency of isolates with virulence to leaf rust resistance genes Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17, and Lr30 for the years 1987-1997. Winter wheats in the southern plains of the United States with resistance genes Lr24, Lr26, Lr11, Lr3ka, Lr17, and Lr16 selected virulent P. triticina phenotypes in the Manitoba and Saskatchewan population. The P. triticina population in Quebec and Ontario was comparatively stable, showing no directional trends in selection of virulence phenotypes. In the Manitoba and Saskatchewan population, diversity of virulence phenotypes changed relatively little despite the selection that occurred in this population. The average number of virulences per isolate in the Manitoba and Saskatchewan population increased from 1987 to 1994 during the period of selection for virulence to Lr24, Lr26, Lr3ka, and Lr11, and declined from 1995 to 1997 when selection for virulence to Lr16 and Lr17 occurred. The most complex virulence phenotypes were not necessarily selected in the Manitoba and Saskatchewan population because of how the resistance genes were deployed in the host population and the nonrandom distribution of virulences in the P. triticina population.Key words: Puccinia recondita f.sp. tritici, specific resistance, wheat leaf rust, Triticum aestivum, specific virulence.
Systematics of North American Petasites (Asteraceae: Senecioneae). III. A taxonomic revision
Authors: Cherniawsky Donna M , Bayer Randall J
Published: April 2011

Petasites Mill. (Asteraceae: Senecioneae) is a taxonomically difficult genus of polygamodioecious, perennial herbs with a widespread distribution across North America. As many as 10 species and as few as two species (Petasites sagittatus (Banks ex Pursh) A. Gray and Petasites frigidus (L.) Fries with three varieties), with one hybrid taxon, have been recognized previously. Considerable taxonomic controversy has surrounded the genus as a result of a conservative floral morphology and a high degree of polymorphism in leaf morphology. Additionally, a number of intergrading leaf forms among those with rather consistent taxonomic characteristics across various treatments have contributed to the taxonomic ambivalence surrounding Petasites. Our taxonomic revision of North American Petasites is based on results obtained from recent multivariate morphometric and isozyme analyses. These data have indicated that taxa of Petasites are not sufficiently differentiated, morphologically or isozymically, from one another to warrant the recognition of separate species. Therefore, Petasites is circumscribed as a single species containing three varietal taxa and one hybrid taxon between two of the varieties. Although our circumscription of P. sagittatus is in accordance with most previous circumscriptions, we have removed it from the rank of species to varietal status under P. frigidus. The new combination Petasites frigidus var. sagittatus (Banks ex Pursh) Cherniawsky is proposed. Subsequent to the new status of one of its parental taxa (P. frigidus var. sagittatus), the new combination for Petasites ×vitifolius (Greene) Bogle is proposed: Petasites frigidus var. ×vitifolius (Greene) Cherniawsky. The three entities of the frigidus complex are united under one polymorphic taxon, P. frigidus var. frigidus and the circumscription and name of Petasites frigidus var.palmatus (Ait.) Cronq. is in accordance with previous authors. A complete list of synonymy and a key to the taxa of Petasites is presented together with distribution maps.Key words: Petasites, Asteraceae, Senecioneae, North America, taxonomic revision.
Host range of Alternaria alternata f.sp. sphenocleae causing leaf blight of Sphenoclea zeylanica
Authors: Masangkay Rhomela F , Mabbayad Maxima O , Paulitz Timothy C , Watson Alan K
Published: April 2011

Forty-eight plant species in 40 genera representing 20 families were screened for susceptibility to Alternaria alternata (Fr.) Keissler f.sp. sphenocleae, a candidate biological control agent for Sphenoclea zeylanica Gaertner (gooseweed). Gooseweed was the only species susceptible to A. alternata f.sp. sphenocleae when plants were treated with 3.5 × 105 conidia/mL (approximately 107 conidia/m2) in the presence or absence of supplemental dew. All inoculated gooseweed plants were killed when subjected to a 14- to 15-h dew. Lactuca sativa L. (lettuce), Glycine max (L.) Merrill (soybean), Phaesolus vulgaris L. (common bean), Psophocarpus tetragonolobus (L.) DC. (winged bean), Vigna radiata (L.) R. Wilcz. (mung bean), Vigna unguiculata (L.) Walp. (string bean), Musa sapientum L. (banana), and some Oryza sativa L. (rice) cultivars showed highly resistant reactions. Brassica oleracea L. (cabbage), Raphanus sativus L. (radish), and Abelmoschus esculentus (L.) Moench (okra) showed highly resistant to moderately resistant reactions while Gossypium hirsutum L. (cotton) showed moderately resistant to moderately susceptible reactions. Symptoms on cotton were restricted to the cotyledons. Sporulation, however, was observed only on detached excised gooseweed leaves, and no sporulation occurred on any of the other plant species evaluated. Gooseweed was the only compatible host plant of A. alternata f.sp. sphenocleae found in these studies.Key words: Alternaria alternata f.sp. sphenocleae, biological weed control, host specificity, gooseweed, Sphenoclea zeylanica.
Patterns of boreal permafrost peatland vegetation across environmental gradients sensitive to climate warming
Authors: Camill Philip
Published: April 2011

This study documents changes in community and functional group across environmental gradients sensitive to climate warming in boreal permafrost peatlands and describes how future changes in temperature and precipitation may lead to changes in species composition and ecosystem properties. At the landscape scale, the presence of permafrost strongly influenced species composition. The position of permafrost thaw affected surface water pH and species composition. At local scales, a combination of water table depth and vegetation structure strongly controlled community composition. Permafrost plateau plots with high Picea mariana basal area were characterized by darker and drier understorey conditions, low cover of Sphagnum fuscum, Ledum groenlandicum, and lichen, and high cover of feather mosses. Aquatic collapse scar plots were dominated by aquatic Sphagnum and Carex, whereas more xeric plots were dominated by hummock Sphagnum and ericaceous shrubs. Functional group responses indicated that changing environmental conditions with climate warming may have significant impacts on community composition and ecosystem processes. A decomposition example is presented to show how changes in species and functional group composition could have important implications for ecosystem-level processes like peat accumulation during climate warming.Key words: bogs, fens, boreal, permafrost, vegetation, ordination
Ovular secretions in the micropylar canal of larches (Larix kaempferi and L. x eurolepis)
Authors: Aderkas Patrick von , Leary Cathy
Published: April 2011

In Larix kaempferi (Lamb.) Carr. and L. × eurolepis A. Henry, a secretion fills the micropylar canal of the ovule during a period of archegonial development that ranges from central cell stage until fertilization. Dissection of the ovuliferous scales caused excess fluid to be exuded from the micropylar canal, forming a drop at the tip of the micropyle. This drop was collected, and its production was quantified. Drop volume was recorded, and the percentage of ovules with drops was counted. The maximum volume of 217 nL far exceeded the volume of the micropyle, which ranged between 18 ± 8 and 28 ± 7 nL (mean ± SD). Removal of drops resulted in further drops being secreted. No drops were produced in ovules that had aborted megagametophyte development.Key words: Larix, micropylar secretions, ovule development.
Water availability alters the relative performance ofSalix sericea,Sralix eriocephala, and their F1hybrids
Authors: Orians Colin M , Bolnick Daniel I , Roche Bernadette M , Fritz Robert S , Floyd Ted
Published: April 2011

Seedlings of Salix eriocephala Michx., Salix sericea Marsh., and their F1hybrids were tested for their growth under contrasting water conditions. One-year old seedlings were grown in pots and subjected to one of two experiments, a scheduled-watering experiment (watered every 1, 4, 8, or 12 days) or a dry-down experiment (no watering after an initial period without water limitation). In the scheduled-watering experiment, short-term growth of hybrids was suppressed relative to the parents. However, subsequent watering allowed hybrids to recover. By the end of the 48-day experiments, hybrids exhibited heterosis across all treatments. In the dry-down experiment, hybrids again were highly susceptible to the onset of drought conditions. From these results, we hypothesize that temporal and spatial variability in water availability could determine the survivorship of hybrids and the frequency of introgression; high water availability may enhance the relative performance of hybrids, while low water availability may limit hybrids.Key words: Salicaceae, willows, hybridization, water relations, performance, heterosis.
Late Quaternary vegetational history of the Howard Pass Area, northwestern Alaska
Authors: Oswald W Wyatt , Brubaker Linda B , Anderson Patricia M
Published: April 2011

Palynological records from Tukuto and Etivlik Lakes contribute to an improved understanding of the late Quaternary history of vegetation in the Howard Pass area of northern Alaska. During the Itkillik II glaciation (24-14 ka BP), the vegetation of the western Arctic Foothills was sparse, xeric tundra, as evidenced by taxa indicative of dry, rocky substrates (e.g., Selaginella rupestris (L.) Spring, Chenopodiaceae, and Encalypta cf. rhaptocarpa) and very low pollen accumulation rates in this interval of the 30-ka-old Tukuto Lake record. Mesic tundra dominated by non-Sphagnum (Bryidae) mosses, Cyperaceae, and Salix species expanded near Tukuto Lake during the late-glacial period, followed by the establishment of Sphagnum moss and increased shrub cover at ca. 10 ka BP. Landscapes around both lakes supported stands of Populus cf. balsamifera during the early Holocene, and Alnus crispa expanded in the Howard Pass area during the middle Holocene. Local variation in plant communities is illustrated by the comparison of the Tukuto and Etivlik pollen records. During the early Holocene, Populus cf. balsamifera was more common near Etivlik Lake than Tukuto Lake, and Juniperus cf. communis was present only in the vicinity of Etivlik Lake. Throughout the middle to late Holocene, Sphagnum, mesic tundra shrubs (Betula nana L., Salix, and Ericaceae species), and minor herbaceous taxa (e.g., Rubus chamaemorus L., Thalictrum, and Caryophyllaceae) were more prevalent at Tukuto Lake than at Etivlik Lake. These differences are likely related to the influence of local landform and soil characteristics near the two sites.Key words: Alaska, Arctic Foothills, Brooks Range, pollen analysis, Quaternary.
Roles of theAfandTlgenes in pea leaf morphogenesis: leaf morphology and pinna anatomy of the heterozygotes
Authors: Villani Philip J , DeMason Darleen A
Published: April 2011

The leaf blade of Pisum sativum L. possesses proximal leaflets and distal tendrils and is altered by two recessive mutations that affect pinna identity, afila (af) and acacia/tendrilless (tl). Using morphological and histology features we characterized the variation in leaf form and pinna anatomy of the Af and Tl heterozygous genotypes. Our goal was to identify the specific interactions of these genes and the relative influence of each in regulating all structural components of the leaf and pinna phenotypes. The Tl/tl genotypes possess broad tendril - narrow leaflets in the distal region that are histologically more similar to leaflets than to tendrils. The afafTltl leaves have simple tendrils in the distal region and branching complexity that is intermediate between that of aftl and af leaves in the proximal region. Only the most distal tips are slightly expanded. Because the Af and Tl genes interact to affect almost all aspects of leaf and pinna form, they affect development at multiple levels of organization.Key words: acacia, afila, Fabaceae, leaf morphology, leaf anatomy, Pisum sativum.
Subterranean structures and mycorrhiza of the achlorophyllous Burmannia tenella (Burmanniaceae)
Authors: Imhof Stephan
Published: April 2011

Plants of the myco-heterotrophic Burmannia tenella Benth. form star-shaped root systems consisting of 0.7-2 mm thick, succulent, brittle roots, reaching lengths of up to 3 cm. In cross section the roots consist of an epidermis, about 10 layers of parenchymatous cortex cells, an endodermis with U-shaped secondary cell wall depositions, and a very reduced central cylinder with two to five central xylem elements and two opposite phloem strands, surrounded by a pericycle of relatively large cells. Based on the thick, aseptate, intracellularly coiled hyphae, arbuscules, and the frequent vesicles, the fungal association of B. tenella is considered to be a Paris-type arbuscular mycorrhiza. The morphological and anatomical structures of the root are discussed in the context of the mycorrhizal dependency of B. tenella. In some root samples, a second fungus with septate hyphae colonized the cortex intracellularly. This fungus restricts the spread of the aseptate symbiont without causing morphological changes to the cortex cells.Key words: Burmanniaceae, root morphology, root anatomy, arbuscular mycorrhiza, myco-heterotrophy, neotropical.
Révision des principales espèces de Fragilariales (Bacillariophyta) des îles Kerguelen
Authors: Le Cohu René
Published: April 2011

Ten species, six of which were previously placed in the genus Fragilaria, were examined, mainly by electron microscopy. Fragilaria germainii Reichardt and Lange-Bertalot is transferred to Diatoma, and Fragilaria alpestris Krasske is transferred to Staurosirella. In Fragilaria capucina Desmazières, one or two rimoportulae are present. In Staurosirella, new details are added concerning the structure of the aerolae; externally, they are multiseriate. Staurosirella pinnata (Ehrenb.) Williams and Round shows an original feature: internal "bridges," perforated by very tiny pores, together join the striae placed on each side of the sternum; moreover, these pores give a particular structure to the striae. In Staurosirella leptostauron (Ehrenb.) Williams and Round, the valvocopula is a closed band with a septum, which is new for this genus. Several species show spinose and nonspinose valves; consequently the presence or the lack of spines does not seem to be an appropriate criterion to distinguish two species.