bluuebunny/crossref_metadata_2025 huggingface dataset:
Impoverishment of vegetation in a coniferous forest polluted by copper and zinc
Authors: Folkeson Lennart , Andersson-Bringmark Ewa
Published: April 2011

Copper and Zn concentrations in raw humus were elevated > 400 and > 80 times, respectively, near an old and a new foundry emitting Cu and Zn but virtually no SO2. Effects on the vegetation were most evident in the ground layer. Four response stages were recognized. (i) Common mosses of mature coniferous forest (Pleurozium schreberi, Hylocomium splendens, Ptilium crista-castrensis, Dicranum polysetum) began to decrease in cover where the Cu and Zn levels in the tissues were 3–5 and 2 times those measured at remote sites, respectively, (ii) Lichens typical of mature dry forest communities (Cladonia subgen. Cladina and C. uncialis) were reduced in cover. (iii) Pioneers typical of successional communities (especially Cladonia subgen. Cladonia) increased slightly in cover, while tolerant mosses retained their cover, (iv) Even the tolerant mosses and lichens disappeared, except for Pohlia nutans. The occurrence of epiphytic lichens decreased. Hypogymnia physodes suffered a reduction in cover and thallus size. The grass Deschampsia flexuosa tended to increase somewhat towards the foundries, but the other field-layer species were unaffected. However, much dead Deschampsia flexuosa has been observed recently close to the new foundry. Environmental variables modified the response of the vegetation to the pollution. Deterioration of the ground layer makes the polluted, thin soil prone to erosion.
Structural and physiological bases for effectivity of soybean nodules formed by fast-growing and slow-growing bacteria
Authors: Lin J. , Walsh K. B. , Canvin D. T. , Layzell D. B.
Published: April 2011

Five weeks after planting, the total dry weight of the association between the soybean cultivar Maple Arrow and the slow-growing rhizobia, Bradyrhizobium japonicum USDA 16, was 1.6 times that with the fast-growing rhizobia, Rhizobium fredii QB1130. In contrast, with the uncultivated variety, 'Peking', the USDA 16 association possessed only 0.58 of the dry weight of the QB1130 association. These growth characteristics could not be fully explained in terms of number or mass of nodules formed. Rather, the specific nodule activity (rate of H2 evolution in Ar–O2 per unit nodule mass) was lower in the poorly effective symbioses ('Maple Arrow' × QB1130; 'Peking' × USDA 16). Nodules of the less effective symbioses were characterized by large deposits of starch in the cortex and in uninfected cells of the central zone, a thick cortical zone, relatively less infected cell area in the central zone, and fewer bacteria per unit crosssectional area of infected cell. Therefore, there were fewer bacteria per nodule in these symbioses. When total nitrogenase activities were expressed per bacteroid number or per bacteroid volume, no significant differences were observed among the four symbioses. These results indicate that the poor effectivity of the 'Maple Arrow' × QB1130 and 'Peking' × USDA 16 symbioses was due to a limitation of either bacterial release from the infection thread or bacterial proliferation within the infected cells.
Interactions between an acute ozone dose, eastern cottonwood, and Marssonina leaf spot: implications for pathogen community dynamics
Authors: Coleman James S. , Jones Clive G. , Smith William H.
Published: April 2011

The effect of an acute ozone dose applied to eastern cottonwood (Populus deltoides Bartr.) on subsequent lesion production of the leaf spot fungus Marssonina brunnea (Ell. et Ev.) P. Magn. was investigated. Two cottonwood clones were exposed to 393 μg∙m−3 (0.20 ppm) ozone for 5 h and then inoculated with conidia of M. brunnea in leaf-disk and whole-plant assays on leaves of different ages (according to the leaf plastochron index (LPI)). There was no significant difference in lesion production on ozone-treated or control foliage, and significantly more lesions were produced on LPI 5 leaves compared with LPI 3, 7, and 9 leaves, irrespective of clone or treatment. These results show that infection of plants by facultative parasites will not necessarily increase when plants are exposed to air pollutants. In another study, urediospore production by an obligate parasite, the cottonwood leaf rust fungus (Melampsora medusae Thum.), was shown to decrease on cottonwood plants treated with an acute ozone dose in comparison with control plants. Thus, we hypothesize that ozone exposure of cottonwoods may have the potential to alter the relative destructive potential and abundance of members of the cottonwood pathogen community by differentially altering host susceptibility to different pathogens.
Genera coelomycetum. XXIII. Catenophoropsis anamorph gen.nov.
Authors: Raj T. R. Nag , Kendrick B.
Published: April 2011

A new anamorph genus, Catenophoropsis, is proposed to accommodate a coelomycete occurring on Eucalyptus leaves in Australia. It has a close affinity with Catenophora, to which a third species is added as Catenophora garyae (Bonar) Nag Raj comb.nov.
Accumulation of polyethylene glycol 6000 and its effects on water content and carbohydrate level in water-stressed tomato plants
Authors: Jacomini E. , Bertani A. , Mapelli S.
Published: April 2011

Young tomato plants were grown in 10 or 25% polyethylene glycol (PEG) 6000 solutions to impose water stress. Plant organs were analyzed to ascertain whether the various plant parts accumulated PEG and to determine the physiological effects. PEG 6000 was taken up by tomato roots and translocated to the shoots. PEG accumulation was greater in roots and in the first leaves and negligible in apical leaves. In all leaves there was an increase in soluble-sugar concentration during the PEG treatment. However, PEG-accumulating leaves showed a delay in dehydration in comparison with leaves where PEG was not accumulated. To explain this behaviour we hypothesize that PEG was accumulated in extracellular spaces and that, as a consequence, water was drawn out from the cells, inducing cellular but not tissue dehydration.
Cytological studies of the M-haustorium of Endocronartium harknessii: morphology and ontogeny
Authors: Hopkin A. A. , Reid J.
Published: April 2011

M-haustoria of the endocyclic rust Endocronartium harknessii (J. P. Moore) Y. Hirat. were examined with light and transmission electron microscopy in infected seedlings of Pinus banksiana Lamb. The haustoria developed from unspecialized cells of the intercellular hyphae, each of which appeared capable of producing several haustoria. The haustoria were distinct from the intercellular hyphae in possessing a narrow septate neck region which terminated in a globose haustorial body. Periodic acid – thiocarbohydrazide – silver proteinate and periodic acid – chromic acid – phosphotungstic acid staining provided evidence of an additional wall layer in the haustorial neck not evident in the intercellular hyphae and suggested that the extra-haustorial matrix contained polysaccharides of mixed linkage as well as lipids. However, cellulase extraction and the use of gold-bound wheat-germ lectin showed that neither cellulose nor chitin, respectively, was a component of the matrix. Both the haustoria and the matrix were separated from the host cytoplasm by the extrahaustorial membrane. This membrane stained positively with periodic acid – chromic acid – phosphotungstic acid, while the noninvaginated portion of the host plasmalemma with which it was continuous usually did not. The matrix fluoresced strongly when stained with aniline blue in an apparently compatible reaction. Other stains such as analinonapthalenesulphonic acid and Calcofluor white showed evidence of protein and polysaccharide in the fungal walls. Light and transmission electron microscope observations showed that penetration pegs formed as narrow tubular evaginations of the haustorial mother cell which caused inward displacement of the host cell wall. They retained their peg-like appearance as they entered the cell lumen, but eventually their distal ends enlarged to form typical globose haustorial bodies.
High-frequency embryogenesis in male sterile plants of Brassica napus through microspore culture
Authors: Chuong Phan V. , Pauls K. P. , Beversdorf W. D.
Published: April 2011

Microspores from several Polima cytoplasmic male sterile (Pol-CMS) and Diplotaxis muralis male sterile (Mur-MS) oilseed rape lines were cultured in a modified Nitsch and Nitsch medium in the dark for 4 weeks. High androgenic frequencies were observed in microspore cultures initiated from plants of both male sterile (MS) types. In cultures maintained at a constant temperature (30 °C) 1 or 2% of the microspores from Pol-CMS or Mur-MS lines, respectively, developed into embryos. A greater percentage of the embryos obtained from the Pol-CMS lines were of good quality than those obtained from the Mur-MS lines (25 vs. 5%). Twenty percent of the plants regenerated from embryos of both lines were spontaneous doubled haploids. The results suggest that no unfavorable cytoplasmic–nuclear genome interaction affecting androgenic potential exists in plants exhibiting Polima or Diplotaxis muralis male sterility.
Large-scale microspore culture technique for mutation–selection studies in Brassica napus
Authors: Polsoni L. , Kott L. S. , Beversdorf W. D.
Published: April 2011

Rapid isolation of oilseed rape (Brassica napus L.) microspores was accomplished by mechanical homogenization of whole racemes with buds no longer than 4.5 mm. After filtration and multiple washes, spores were incubated overnight in liquid medium at 30 °C in the dark, before plating in fresh medium at a density of 100 000 spores/mL. After 14 days in culture, gentle agitation on a shaker improved the rapid development of normal embryos and later, when transferred to light and liquid B5G medium (B5 + 0.1 mg/L gibberellic acid), further agitation enhanced the rate of maturation and germination. With this method 200–400 million spores can be processed in one batch, resulting in a final yield of several hundred thousand embryos within 3 weeks. Applications of the system for mutation–selection in B. napus are outlined.
Dinemasporium lanatum anam.- sp.nov. from Cuba
Authors: Raj T. R. Nag , Ruiz Rafael F. Castañeda
Published: April 2011

A new species of Dinemasporium, occurring on decaying leaves of an undetermined tree in a leaf litter sample, is reported from Cuba.
Flax rust from Linum marginale: pathogenicity reactions on the Linum usitatissimum set of differential varieties
Authors: Lawrence G. J.
Published: April 2011

Flax rust, Melampsora lini (Ehrenb.) Lév., occurs on Linum marginale Cunn., the only Linum species indigenous to Australia. Evidence suggests that the rust is native to L. marginale and is not a recent introduction. Forty-five isolates from this rust population, collected from 21 locations, were tested for reaction type on the standard set of 28 flax (L. usitatissimum) differential lines. All isolates were avirulent on the majority of differentials and only three clearly different virulence phenotypes were distinguished. This finding contrasts with the results of a companion study in which the same isolates displayed many different virulence phenotypes when tested on a set of L. marginale lines. Two factors apparently contribute to the failure of the L. usitatissimum differentials to detect most of the variation for virulence present in this rust population. First, 10 of the differentials have been reported to possess resistance gene L9 in addition to their designated gene. Since all isolates recognize the L9 gene, these differentials could make no contribution to differentiating between the isolates. Second, many of the L. usitatissimum resistance genes apparently do not occur in L. marginale and with no selection on the rust to conserve or evolve the corresponding virulence genes, the corresponding avirulence genes appear to have become, or remained, fixed in the rust population.
A synopsis of the genus Medicago (Leguminosae)
Authors: Small Ernest , Jomphe Marcel
Published: April 2011

The genus Medicago has recently undergone extensive taxonomic changes. At least two dozen species not previously accepted as belonging to it have been added. Moreover, the circumscription, infraspecific taxonomy, and nomenclature of many of the species placed in Medicago have been altered recently, and the circumscription and nomenclature of the sections of the genus have also changed. Adding to the need for a synopsis is the fact that many of the species are very difficult to identify. This conspectus presents a key to the 12 sections and eight subsections of the genus, a comprehensive illustrated key to the 83 species (and 18 infraspecific taxa) of Medicago, and brief notes on their geography, ecology, and possible confusion with similar species.
Genera coelomycetum. XXVII. Pycnovellomyces redescribed
Authors: Raj T. R. Nag , Holubová-Jechová Vĕra , Castañeda Ruiz Rafael F.
Published: April 2011

Examination of the type specimen of Pycnovellomyces foliicola Castaneda has revealed that this bizarre coelomycete has basidiomycetous affinities. The fungus is redescribed and the generic concept is revised to reflect the new information.
Morphologie pollinique des Cupressaceae de l'est du Canada et du nord-est des États-Unis appliquée à l'étude des sédiments quaternaires
Authors: Parent Johanne , Richard Pierre J. H.
Published: April 2011

The pollen morphology of seven species, varieties and forms of Cupressaceae from eastern Canada and northeastern United States was studied by light microscopy, following acetolysis, to improve the identification of these taxa in Quaternary fossil sediments. Taxodium distichum (Taxodiaceae), which is also present in the study area, was included for comparison. Four pollen types were defined: Juniperus communis – Thuja occidentalis, Chamaecyparis thyoides, Juniperus horizontalis – Juniperus virginiana, and Taxodium distichum. Five shapes of pollen grains exist: whole, slightly split, opened in a "V" shape, spindlelike, or split in halves. All shapes are found in all species, in varying proportions, and represent different stages of hydration in Cupressaceae pollen type. The absence or presence of these shapes cannot be used as an identification criterion for the different species. A pollen identification key, applicable to fossil sediments and combining characters based on shape, size and other morphological features of acetolysed grains, is proposed and allows to differentiate all the species from one another, with the exception of Juniperus horizontalis and Juniperus virginiana.
Virus-like particles in hyphae and conidia of European hypovirulent (dsRNA-containing) strains of Cryphonectria parasitica
Authors: Newhouse Joseph R. , MacDonald William L. , Hoch Harvey C.
Published: April 2011

Hyphae and germinating conidia of European hypovirulent (dsRNA-containing) Cryphonectria parasitica strain Ep-50 and virulent (dsRNA-free) strain Ep-67 (isogenic derivative from Ep-50), and hyphae only of European hypovirulent (dsRNA-containing) strains Ep-4 and Euro-7 were freeze-substituted and examined for the presence of virus-like particles (VLPs) using transmission electron microscopy. Spherical, membrane-bounded VLPs, measuring 50–90 nm in diameter, were located in hyphae and conidia of hypovirulent strain Ep-50, but not virulent strain Ep-67. Hyphae of hypovirulent strains Ep-4 and Euro-7 contained VLPs similar to those found in Ep-50. The VLPs occurred in aggregates surrounded by rough endoplasmic reticulum or more rarely, scattered throughout the cytoplasm; most possessed an electron-dense core. Results of Bernhard's regressive staining technique and lipid extraction cytochemistry suggested that the particles consisted of RNA surrounded by a lipid membrane. A unique Golgi body was associated with the formation of VLPs in hypovirulent strain Ep-50. The VLPs do not resemble typical fungal viruses and may be the end product of a defense response on the part of the fungal host designed to wall off foreign nucleic acid. Key words: Endothia parasitica, mycovirus, defense response, hypovirulence, viroid, fungal Golgi.
Anthropogenic stress and natural selection: variability in radish biomass accumulation increases with increasing SO2 dose
Authors: Coleman James S. , Mooney Harold A. , Winner William E.
Published: April 2011

Although there is a strong relationship between genetically based variability of a given character and the potential for natural selection to act on that character, most studies of the effects of environmental factors on plants examine the mean responses of plants in a population and not the variability among plants in the population. Yet variability in the response among individuals to an environmental stress could foretell changes in a population that might not be evident from examination of mean responses. Here we report an analysis of data from several experiments on radish plants showing a significant relationship between the coefficient of variation for biomass production by radish plants and the concentration of SO2 at which these plants were fumigated. Increased variability as a result of SO2 exposure may have been due to genotypic differences in SO2 resistance among plants, suggesting a route by which the rapid selection of SO2 resistant plant populations may occur in habitats characterized by severe SO2 stress. Increased variability may have also been due to the effect of SO2 on processes controlling phenotypic plasticity of radish growth. Since SO2 affected variability without necessarily affecting mean plant growth, these results also show that examination of variability in the responses of plants to stresses may be equally or more biologically meaningful than sole examination of mean responses. Furthermore, these results show that care must be taken when constructing parametrically derived dose–response models for predicting the effect of SO2 on plants. If it is common for SO2 to increase the amount of variation in plant populations, then parametric statistical functions would be an inappropriate tool for predicting the effect of SO2 on plants.
The influence of snow on subalpine meadow community pattern, North Cascades, Washington
Authors: Evans R. D. , Fonda R. W.
Published: April 2011

The relationships among community pattern, date of snowmelt, and microclimate were examined on Excelsior Ridge in the North Cascades. Nine communities were delineated and placed into three groups based on date of snowmelt and topographic location. The Veratrum viride, Valeriana sitchensis, Lupinus latifolius, and Carex spectabilis communities, all found on windward slopes, were released from snow from June to mid-July. The Phyllodoce empetriformis, Vaccinium deliciosum, and Saxifraga tolmiei communities were located on leeward slopes where snow melted in July. Sheltered basins, which retained snow until late July or early August, supported the Carex nigricans and Luetkea pectinata communities. The influence of time of snowmelt generally was reflected in soil temperature, so that earlier sites were warmer than later sites. A soil moisture gradient was not apparent among any of the communities.
Some aspects of the phytogeography of Carex
Authors: Ball P. W.
Published: April 2011

The worldwide distribution of Carex suggests that it originated in the early Tertiary. The genus reaches its greatest diversity in the temperate regions of the world. Except for SE Asia, it is generally absent from lowland tropical areas and is especially rare in Africa. Subgenus Indocarex, although abundant in SE Asia, also occurs in east Africa, the Mediterranean region, and tropical America. Such a distribution is consistent with the view that the subgenus originated in the early Tertiary, adjacent to the Tethys seaway. The genus contains a variety of species or species groups that exhibit disjunct distribution patterns such as bipolar, amphiatlantic, and eastern Asia – eastern North America distributions. The evidence in most of these examples favours a relatively late origin for these distributions. A number of sections contain species complexes in which several closely similar species are sympatric and show little ecological differentiation. At the moment we have no satisfactory explanation of the processes of speciation and migration that led to this situation.
The effect of SO2 on the vesicular–arbuscular mycorrhizae associated with a submontane mixed grass prairie in Alberta, Canada
Authors: Clapperton M. Jill , Parkinson Dennis
Published: April 2011

We investigated the effect of long-term exposure to sulphur-based acid-forming emissions (primarily sulphur dioxide) on a submontane mixed grass prairie and the associated vesicular–arbuscular mycorrhizae (VAM). Three prairie field sites were selected at distances of 5, 13, and 20 km from a sour gas processing plant that had been operating for approximately 23 years. The sites were selected for similarity of vegetation and soils. The soil at site 1 showed symptoms of acidification as did the soil from site 2, but to a lesser extent. The VAM inoculum potential was also significantly lower in soil from site 1, and to a lesser extent from site 2, compared with soil from site 3. These results are discussed in terms of the effects of sulphur dioxide on the field sites and its subsequent effect on the VAM.
Inflorescence development in Amelanchier alnifolia
Authors: Steeves Margaret W. , Steeves Taylor A.
Published: April 2011

The morphology and development of the inflorescence of Amelanchier alnifolia, a potential fruit crop, are described. Although racemelike in appearance, the 8- to 12-flowered inflorescence is determinate, and the occasional branching of the basal member indicates its compound nature. This basal member in the axil of a foliage leaf frequently bears three to four bracteoles instead of the two characteristic of the remaining lateral flowers, and an arrested bud may be found in the axil of one or more of the bracteoles. The inflorescence is thus interpreted as a much reduced panicle. The phenology of inflorescence development in relation to seasonal shoot growth has been documented. Transformation of vegetative shoot apices to the flowering condition begins after the differentiation of a set of cataphylls and as the current fruit crop is ripening. It is marked by the accelerated formation of bract primordia with precocious axillary buds, culminating after about 2 weeks with the initiation of a terminal flower. Although the last to be formed, the terminal flower at all subsequent stages is equivalent in development to those at the base of the inflorescence. The buds in the axils of three to five bracts immediately below the terminal flower are arrested at an early stage and variation in inflorescence size may in part be due to variability in their development.
Comparative studies of protoplast development in jack pine (Pinus banksiana)
Authors: Tautorus T. E. , Fowke L. C. , Dunstan D. I.
Published: April 2011

Protoplasts were isolated either from the cotyledons of 8- to 10-day-old seedlings, or from cell suspensions, initiated from seedlings of the same open-pollinated seedlot of jack pine (Pinus banksiana Lamb.). Protoplast yields were 2.0 – 7.0 × 105/g fresh wt. for cotyledon-derived, and 0.3–5 × 105/g fresh wt. for suspension-derived protoplasts. Cotyledon protoplasts (6.8%) divided after 5 to 8 days incubation in liquid Lainé medium C with 450 mM glucose as osmoticum. Small clusters of 6 to 10 cells, which were observed after approximately 2 weeks, formed microcalli upon further dilution of the culture medium. By 6 to 8 weeks, these microcalli could be transferred to solid medium using a nurse culture of jack pine cells. Protoplasts isolated from seven cell suspension lines differed in their responses to culture conditions. First divisions were only observed with two cell lines cultured in either Lainé medium C or one-half Litvay with 370 mM glucose, but this did not lead to callus development. Key words: jack pine, Pinus banksiana, cotyledons, protoplasts, regeneration, callus.
Ultrastructural relationships of the developing syncytium induced by Heterodera schachtii (Nematoda) in root tissues of rape
Authors: Magnusson Christer , Golinowski Władysław
Published: April 2011

The growth and development of the syncytium induced by the beet cyst nematode (Heterodera schachtii Schmidt) in rape (Brassica napus var. oleifera) and its relationships to adjacent root tissues were studied by serial sectioning and electron microscopy. In a 5-day-old syncytium, xylem parenchyma cells formed the largest part of the syncytium volume, while pericycle cells constituted the smallest fraction. Xylem parenchyma cells outside the confluent part of the syncytium were the first cells to differentiate into syncytium-component cells at the leading edges of syncytia. Early stages of differentiation were characterized by an increase in ribosomes and rough endoplasmic reticulum. Later stages involved formation of tubular structures and cell wall ingrowths. In lateral roots, into which main root syncytia extended, xylem differentiation was disturbed by strong hypertrophy of xylem parenchyma cells. Here, xylem tracheary elements similar to graniferous tracheary elements occurred. The parasitism of H. schachtii in rape induced dramatic changes in root morphogenesis, and the response of xylem parenchyma cells was of fundamental importance in this host–parasite system. Key words: Brassica napus, Heterodera schachtii, syncytium, ultrastructure.
Tubular structures in developing plastids of three dicotyledonous species
Authors: Oross J. W. , Possingham J. V.
Published: April 2011

Tubular structures were observed in the developing plastids of the meristematic regions of spinach, beet, and turnip leaves. These structures were located near the plastid periphery, were frequently in contact with the plastid envelope and (or) the internal plastic membranes, usually had a near-perpendicular orientation with their associated membranes, and were decorated with a distinct striated coating. Based on the high degree of structural similarity, it was suggested that these tubules represent a unique class of plastid inclusions with a common specialized function. A detailed examination of the spinach plastids provided evidence that the tubules are membranous structures and that the tubular lumen is confluent with that of the plastid envelope and also some internal plastidial compartments. It was also shown that the membranes of the tubules differed from the other plastidial membranes in that they were thinner and only lightly stained by osmium – potassium ferrocyanide postfixation. Key words: tubular, structures, developing, plastids, dicots.
Morphological, cytochemical, and ontogenetic characteristics of a new species of vesicular–arbuscular mycorrhizal fungus
Authors: Giovannetti Manuela , Avio Luciano , Salutini Loredana
Published: April 2011

The new species of endomycorrhizal fungus Glomus coronatum Giovannetti is described using morphological, cytochemical, and ontogenetic characters. Spores are yellow–orange to red–brown, globose, with a hyaline outer wall layer expanding into roughened, flamelike columns in acidic mountants. Sporocarps are formed by the growth of fine hyphal branches from the subtending hyphae, which gradually cover the original spore. Many of the spores enveloped in the hyphal mantle are formed simultaneously and coalesce to form the sporocarp. The importance of the ontogeny of spores and sporocarps in the description of new taxa is discussed. Key words: mycorrhizae, VAM fungi, taxonomy, ontogeny, Glomus coronatum.
Interrelationships of poplars in a hybrid swarm as studied by gas chromatography – mass spectrometry
Authors: Greenaway W. , English S. , Whatley F. R. , Rood S. B.
Published: April 2011

Analysis of bud exudate by gas chromatography-mass spectrometry (GC–MS) of 14 clones belonging to a natural hybrid swarm involving Populus angustifolia, P. balsamifera, and P. deltoides produced results consistent with those obtained by previous analysis of leaf characteristics. Specimens that had leaves most characteristic of a pure species also produced bud exudate GC–MS profiles which were characteristic of those species. GC–MS profiles of interspecific hybrid clones were intermediate between the parental species. This demonstrates the usefulness of GC–MS analysis of bud exudate as a chemo-taxonomic method for the study of intersecific poplar hybrids and also supports the accuracy of analysis of foliar morphology for taxonomic assessment. Key words: Populus, bud exudate, gas chromatography – mass spectrometry.
Two additional species of the genus Togninia
Authors: Hausner G. , Eyjólfsdóttir G. G. , Reid J. , Klassen G. R.
Published: April 2011

Two potential wood-staining fungi that superficially resemble species of the genus Ceratocystis s.l. were investigated employing morphological criteria and rDNA analysis. After morphological comparison with Togninia minima (Tul. and C. Tul.) Berl., they are assigned to Togninia as Togninia fraxinopennsylvanica (Hinds) n.comb. and Togninia novae zealandiae n.sp. Key words: Togninia, Ceratocystis, taxonomy, morphological, molecular.
Effet du NaCl sur l'utilisation des lipides et les activités enzymatiques glyoxysomales au cours de la germination de deux espèces de Medicago
Authors: Miled-Daoud Douja Ben , Cherif Abdelkader
Published: April 2011

The effect of increased NaCl concentrations on seed germination of two Medicago species (M. orbicularis and M. murex) was studied during the first 10 days of development. The effect of NaCl on utilization of storage lipids and on glyoxysomal marker enzymes in cotyledons was also examined. Total lipids, total fatty acids, and triacylglycerols decreased significantly with seedling growth in control cotyledons. Storage lipids disappeared as glyoxysomal enzyme activity appeared. The effect of NaCl on utilization of storage lipids and on glyoxysomal enzyme activity is compared for the two species. Key words: Medicago, germination, NaCl, lipids, glyoxysomal enzymes.
Effects of Ca2+ on the growth of Dunaliella tertiolecta in media with high concentrations of Mg2+
Authors: Fujii Shuhei , Hellebust Johan A.
Published: April 2011

The growth rate of Dunaliella tertiolecta in a high MgSO4 (0.94 M) medium was lower than that in a NaCl medium of the same osmolality. Growth inhibition of D. tertiolecta in the high MgSO4 medium was partially relieved in response to increases in extracellular Ca2+ concentrations (1 – 11 mM). This growth recovery effect by supplemental Ca2+ was eliminated by the simultaneous additions of ethylene glycol-bis-(β-aminoethyl ether)-N′,N′-tetraacetic acid. The measurements of intracellular cations revealed that the intracellular concentration of Ca2+ increased with increases in the extracellular Ca2+ concentration. From the kinetic analysis of the relationship between the extracellular Ca2+ concentration and the growth in media containing various concentrations of Mg2+, Ca2+ was found to interact competitively with Mg2+ with regard to growth of D. tertiolecta in MgSO4 media. These results indicate that high concentrations of Mg2+ inhibit the uptake of Ca2+ into cells, resulting in the observed growth inhibition in MgSO4 media. Key words: Dunaliella, magnesium, calcium, antagonistic effect.
Holocene vegetation history of the boreal forest near Chibougamau, central Quebec
Authors: Garralla Silvina , Gajewski K.
Published: April 2011

A pollen diagram from a small lake in the region of Chibougamau (49°41′N, 74°35′W; elevation 380 m), central Quebec, is divided into four pollen assemblage zones. Before 7600 BP the landscape was open shrub tundra and the pollen input to the lake was primarily from long-distance sources. Larix, and to a lesser extent Populus, were important colonizers of the newly deglaciated land, and Picea was also present. Betula papyrifera and Picea dominated the open forests between 7600 and 4700 BP. After 4700 BP the forest became more dense and the importance of Betula papyrifera suggests relatively warm and dry climatic conditions. Around 3900 BP Picea, Ericaceae, and Sphagnum increased in abundance at the expense of Betula, suggesting cooler, wetter conditions. Pinus banksiana increased during this period but was never very abundant. The modern boreal forest thus developed relatively late in this region and has been present for only the past 2000–3000 BP. Key words: paleoecology, Quebec, Holocene, boreal forest, Betula papyrifera, Picea.
Cost of reproduction in Douglas-fir
Authors: El-Kassaby Yousry A. , Barclay Hugh J.
Published: April 2011

The balance between allocating energy resources to reproduction or growth has considerable theoretical interest. Conflicting ecological requirements and evolutionary pressures often necessitate a trade-off in energy allocation. We obtained measurements on seed-cone production and annual ring width of 365 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees from 29 open-pollinated families for 8 years. Phenotypic, genetic, and environmental correlations were computed for seed-cone production and ring width for each year. Five of the eight environmental correlations were negative (range −0.077 to −0.305), reflecting the reality of the trade-off in physiological terms. Six of the eight genetic correlations were negative (range −0.199 to −0.776), indicating that a trade-off exists at the genetic level between energy allocation to reproduction and to somatic growth. These findings agree with the current theory of life-history evolution. Key words: Pseudotsuga menziesii, cone production, annual ring width, genetic correlation.
Herbicide-induced resistance of cotton to Verticillium wilt disease and activation of host cells to produce the phytoalexin gossypol
Authors: Awadalla O. A. , El-Refai I. M.
Published: April 2011

Pretreating cotton seeds with selected herbicide markedly increased cotton resistance to vascular wilt caused by Verticillium albo-atrum. The present investigation studied the mechanism of resistance to V. albo-atrum induced by some herbicides in susceptible cotton plants. The three herbicides tested repressed mycelial growth. Prometryn and dalapon caused a marked reduction in the appearance of Verticillium wilt disease and were the most effective in controlling the disease. Phytoalexin (gossypol) production was greatly increased in herbicide-treated inoculated cotton plants. The level of gossypol was higher in the root than stem. Maximum production of gossypol was achieved in cotton plants treated with the herbicides prometryn and dalapon and inoculated with fungal spores but it was not present in uninoculated control plants. Key words: cotton, Verticillium albo-atrum, herbicides, phytoalexin, disease resistance.
Relationships of mycorrhizal symbiosis, rooting strategy, and phenology among tallgrass prairie forbs
Authors: Hetrick B. A. D. , Wilson G. W. T. , Todd T. C.
Published: April 2011

The response of 23 tallgrass prairie forbs to mycorrhizal symbiosis and P fertilization was assessed in steamed and non-sterile prairie soil. For each plant species, root diameters, root fibrousness, root to shoot ratio, plant dry weight, mycorrhizal root colonization, mycorrhizal dependence, P dependence, and phenology were measured. Using these data, cluster analysis, stepwise discriminant analysis, and canonical discriminant analysis of the data revealed that the forbs could be divided into three distinct groups based on mycorrhizal dependence, root morphology, and phenology in descending order of importance. Cluster groups 1 and 2 contained obligately and facultatively mycotrophic forbs, respectively, while the third group did not benefit from the symbiosis. Models for prediction of mycorrhizal dependence, constructed using stepwise regression analysis, were based largely on root fibrousness. A regression analysis comparing mycorrhizal dependence and root fibrousness was conducted, and group means and 95% confidence ellipses were examined for each group. These revealed that the mycorrhizal dependence and root fibrousness of groups 1 and 3 are relatively constant regardless of P level, while the response of forbs of group 2 is more plastic, i.e., mycorrhizal dependence decreases and root fibrousness increases as P level increases. The relationship between plant response to mycorrhizal symbiosis and life strategy or growth pattern is discussed. Key words: mycorrhizal dependency, vesicular–arbuscular mycorrhizae, root systems.
Inhibition of deoxynivalenol translocation and fungal colonization in Fusarium head blight resistant wheat
Authors: Snijders C. H. A. , Krechting C. F.
Published: April 2011

Ergosterol analyses of seed samples infected with Fusarium culmorum from 22 wheat genotypes differing in resistance to Fusarium head blight indicated that visual assessment of head blight levels from a field plot gives a reliable estimate of the amount of fungal biomass. The percentage of infected spikelets was a better indication of the amount of fungal biomass present than the percentage of infected heads. This suggests that Fusarium head blight resistance in this population is mainly based on resistance to colonization and that resistance to establishment of the initial infection plays only a minor role. Plants from a susceptible and a resistant breeding line were inoculated with F. culmorum at flowering time. Four weeks after inoculation heads were selected with Fusarium-infected spikelets levels ranging from 0 to 100%. At this time only low levels of ergosterol were detected in the kernels. Eight weeks after inoculation, ergosterol concentrations in chaff and kernels were significantly higher in the susceptible line compared with the resistant breeding line. At 4 and 8 weeks after inoculation the trichothecene deoxynivalenol content of chaff and kernels was also much higher in the susceptible line than in the resistant line. The Fusarium head blight resistant line possesses resistance to hyphal invasion. It appears that deoxynivalenol is transported from the chaff to the young kernel and the pathogen then colonizes the kernel. In the resistant line deoxynivalenol translocation from chaff to kernel was inhibited and little fungal colonization occurred. It is hypothesized that this is based on a membrane-based trichothecene tolerance. Key words: wheat, Fusarium, trichothecene, resistance, ergosterol, deoxynivalenol.
The ultrastructure of ascosporogenesis in freeze-substituted Thelebolus crustaceus: enveloping membrane system and ascospore initial development
Authors: Czymmek Kirk J. , Klomparens Karen L.
Published: April 2011

High-pressure and propane-jet freezing were essential for determining the origin and development of the enveloping membrane system during ascosporogenesis in Thelebolus crustaceus. Prior to the completion of mitotic divisions within the ascus, invaginations of the plasma membrane initiated formation of the enveloping membrane system. Fusion of individual units of the closely spaced double membranes resulted in the formation of a cylinder around most of the ascus protoplasm. This double-membraned cylinder enveloped individual nuclei with accompanying cytoplasm and organelles to form ascospore initials. Envelopment of asci nuclei to form ascospore initials appeared to be facilitated by a nuclear-associated organelle and closely associated microtubule organizing center. Initially, wall materials and (or) precursors were deposited between the closely spaced double membranes from within the ascospore initials. Secondary wall formation appeared to be deposited, in part, from the epiplasm. Microtubules located adjacent to the inside wall layer of the ascospore initials appeared to contribute to an elliptical shape. Subsequent to epispore wall formation, numerous microtubules were found associated with the outer membranes of the ascospores and appeared to interconnect the spores into a single mass before discharge. Key words: Thelebolus crustaceus, ascosporogenesis, high-pressure freezing, propane-jet freezing, ultrastructure, laser scanning confocal microscopy.
Croissance rythmique endogène de la feuille de Guarea guidonia (Méliacées): Étude préliminaire expérimentale
Authors: Miesch R. , Barnola P.
Published: April 2011

The composed pennate adult leaf of Guarea guidonia (Meliaceae) has a multiannual rythmic growth shown by the successive sequential setting of leaflet pairs. This is demonstrated at the level of the foliar central vein by the differentiation of periodic rings in the wood. Microsurgically isolated foliar primordia produced large leaves, the tops of which supported several foliar sequences. Early removal of foliar primordia suppressed the endogenous rythmic growth pattern and the functioning of the foliar apex became continuous. Isolated cuttings of the composed leaf were readily rooted, the rythmic growth being maintained. This was also possible with cuttings of isolated nodes. Data show that rooted cuttings of this plant could be used as a model for the study of endogenous rythmic growth of woody plants. Key words: Guarea guidonia, composed leaf, endogenous rythmic growth, root cutting. [Journal translation]
Studies of mature seeds of eleven Pinus species differing in seed weight. II. Subcellular structure and localization of elements
Authors: West M. M. , Lott J. N. A.
Published: April 2011

Seed tissues of 11 species of Pinus, varying greatly in seed weight, all contained protein bodies with one or more protein crystalloids and (or) one or more globoid crystals. Protein body structure and the types of elements stored in globoid crystals of protein bodies were similar between female gametophytes and their embryos. Energy dispersive X-ray analysis of globoid crystals revealed the presence of P, K, and Mg, a finding consistent with their being phytate rich. Traces of Ca and Fe were also detected in globoid crystals of some tissues. The P and Mg levels in globoid crystals of embryo and female gametophyte tissues decreased as interspecific seed tissue weight increased. High levels of Fe and significant levels of P, K, and Mg were detected in small, often ≤ 0.33 μm, naturally electron-dense particles distributed in all tissues of the embryo and female gametophyte. Unlike conventional phytate-rich globoid crystals, these Fe-rich particles were not contained in typical protein bodies but were contained within membrane-bound structures that may be plastids. Iron levels of the Fe-rich particles of Pinus seed tissues decreased as seed tissue weight increased. Key words: Pinus, seed weight, energy dispersive X-ray analysis, globoid crystals, Fe-rich particles.
Development of infection structures by Hemileia vastatrix in resistant and susceptible selections of Coffea and in Phaseolus vulgaris
Authors: Coutinho T. A. , Rijkenberg F. H. J. , Asch M. A. J. van
Published: April 2011

The sequence of events leading to successful infection of Coffea by Hemileia vastatrix, following the formation of an appressorium over a stoma, was investigated using scanning electron microscopy. In the host, Coffea arabica, a torpedoshaped substomatal vesicle initial develops bilaterally from the apex of the infection wedge, while in the nonhost, Phaseolus vulgaris, the infection wedge protrudes into the substomatal chamber. The substomatal vesicle in both host and nonhost, at 48 h postinoculation, is anchor shaped. Haustorial mother cells are formed on stubby primary infection hyphae that curve back onto subsidiary cells. No differences in appearance of these structures were noted between resistant and susceptible coffee selections. A much-branched mycelium ramifies through the intercellular spaces of the mesophyll cells 96 h postinoculation in the host. In bean, the SSV began to collapse 48 h postinoculation. Key words: coffee leaf rust, infection, penetration, Coffea, appressorium, substomatal vesicle.
Mefluidide-induced drought resistance in seedlings of three conifer species
Authors: Silim Salim N. , Guy Robert D. , Lavender Denis P.
Published: April 2011

Short-term effects of the plant growth retardant mefluidide on drought resistance were investigated in seedlings of western red cedar (Thuja plicata Donn), yellow cedar (Chamaecyparis nootkatensis D. Don), and white spruce (Picea glauca (Moench) Voss). Mefluidide was applied as a root drench at concentrations of 0, 0.1, and 0.4 mg∙L−1. Following this, seedlings were stressed by withholding water for a period of up to 7 days and then watering regularly thereafter. Stomatal conductance of the mefluidide-treated seedlings decreased significantly and remained lower than the control seedlings throughout the stress period. As a result of the decreased conductance, shoot water potentials in mefluidide-treated seedlings remained higher throughout the stress period. There was a decrease in net photosynthesis that was partially caused by stomatal limitations, the severity of which depended upon the concentration of mefluidide applied. Mefluidide treatment also resulted in an accumulation of abscisic acid in all three species, and this may have been responsible for the effects on stomatal conductance and water relations. In contrast, the mefluidide-treated seedlings had the highest rates of photosynthesis after rewatering, resulting primarily from a promotion of stomatal opening. Key words: stomatal conductance, water potential, photosynthesis, plant growth inhibitors, abscisic acid, cold hardiness.
Nucleation during primary succession in the Canadian Rockies
Authors: Blundon D. J. , MacIsaac D. A. , Dale M. R. T.
Published: April 2011

A study of nucleation during primary succession was carried out on age sequences of communities at two sites in the Canadian Rocky Mountains: one at the Mount Robson moraines, British Columbia, the other at Southeast Lyell Glacier, Alberta. The study concentrated on the associations of species with the nitrogen-fixing plants Hedysarum boreale var. mackenzii at Mount Robson moraines and Dryas drummondii at Southeast Lyell Glacier because those plants might serve as nuclei for colonization by other species, thus facilitating succession. The data show that recruitment of later successional species is greater in patches of the two pioneer species, but the fact that recruitment takes place away from the plants also suggests that although there is nucleation, it is not necessary for succession at these sites. Key words: colonization, nitrogen fixation, nucleation, succession.
A 12 000 year record of vegetation change and soil development from Wien Lake, central Alaska
Authors: Hu Feng Sheng , Brubaker Linda B. , Anderson Patricia M.
Published: April 2011

Pollen, plant-macrofossil, macroscopic-charcoal, and geochemical analyses of a sediment core from Wien Lake provide new information on the late Quaternary environmental history of central Alaska. Shrub tundra dominated by Betula glandulosa occupied the area 12 000 – 10 500 BP. Low plant cover and intensive soil erosion of the tundra landscape are indicated by low pollen-accumulation rates, high sediment inorganic content, and high allogenic elemental concentrations. Around 10 500 BP, Populus and Salix invaded the shrub tundra and open ground to form dense stands within the lake catchment. The marked increases in sediment organic content and authigenic concentrations of Fe, Mn, and Al during the period of Populus–Salix dominance suggest humic buildup and stabilization of the catchment soils. These soil changes in turn may have contributed to the demise of Populus–Salix communities 9500 BP. Fossil seeds indicate that Betula papyrifera arrived 9500 BP, rather than in the middle to late Holocene as suggested by previous palynological studies. Picea glauca codominated open woodlands with B. papyrifera 9500 – 7500 BP. The decline of Picea glauca 7500 BP was probably due to an episode of climatic cooling rather than autogenic processes resulting in waterlogged soils. Alnus arrived in the region 7500 BP. After 6500 BP, modern boreal forest dynamics are indicated by the dominance of Picea mariana, fluctuations of Picea glauca, and frequent occurrence of local fires. Key words: late Quaternary paleoecology, Alaska, vegetation and soil history, pollen, plant-macrofossils, geochemistry.