bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosynthesis and transpiration in large forest-grown Douglas-fir: diurnal variation
Authors: Leverenz Jerry W.
Published: April 2011

Net photosynthesis, transpiration, and stomatal conductance of terminal shoots of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were measured using an open gas exchange system. Correlations between these physiological parameters and environmental variables on an overcast day, a cool partly sunny day, and a day of high temperature and leaf–air vapor pressure difference are presented. Diurnal variation in shoot water potential and intercellular space CO2 concentration had little effect on the physiological parameters. Leaf–air vapor pressure difference and (or) leaf temperature had considerable influence on days of high temperatures. Net photosynthetic rate was strongly correlated with photon flux density on completely overcast days.Stomatal conductance exerted little control on diurnal variation of net photosynthetic rates on overcast days because stomatal conductance saturated at lower photon flux densities than net photosynthesis. When net photosynthesis was light saturated parallel responses of stomatal and residual conductances to vapor pressure difference and (or) leaf temperature occurred. Intercellular space CO2 concentration remained fairly constant when net photosynthesis was light saturated.
South Indian agaricales. X. Hemimycena indica sp.nov.
Authors: Natarajan K. , Manjula B.
Published: April 2011

An interesting agaric, Hemimycena indica sp.nov., collected from South India is described and illustrated.
Hyalopycnis blepharistoma: a pycnidial basidiomycete
Authors: Bandoni R. J. , Oberwinkler F.
Published: April 2011

Morphology and development of Hyalopycnis blepharistoma (Berk.) Seeler are discussed. The presence of infrequent clamp connections, dikaryotic hyphal cells and conidia, and the colour reaction with diazonium blue B all suggest that H. blepharistoma is a basidiomycete. However, failure to observe a basidial stage precludes assignment to known orders of basidiomycetes.
Variation de la durée des cycles cellulaires au cours du passage de l'état jeune à l'état adulte dans le méristème caulinaire du Polypodium vulgare
Authors: Michaux-Ferrière Nicole
Published: April 2011

During the development of Polypodium vulgare L. mitotic indices and duration of cell cycles have been determined for two apical zones of the meristem. In the young state, the mitotic activity of the meristem is high and uniform; the cell cycles of the axial and lateral zones are very similar. At the beginning of the adult state, the axial zone is characterized by a low mitotic index and a cell cycle which is twice that of the lateral zone.
Rhizogénèse adventive dans l'épicotyle du Pois : initiation et structuration de la racine
Authors: Nougarède A. , Rondet P.
Published: April 2011

The ability of the first internode of Pisum sativum epicotylary axis to produce adventitious roots was examined with respect to dark and light growing conditions and depth position of the soaked seeds in vermiculite. Root initiation began on the 7th day and moved acropetally until the 16th day, with no formation of new roots between older ones. DNA synthesis in the diploid interfascicular cells followed the first mitoses of root initiation. The cell layer that would normally have differentiated into an endodermis reacted more slowly and built a primordial root cap, protecting the root as it grew through the cortex. When the new root emerged a new root cap – protoderm complex was rebuilt from the subapical cells of the root meristem. The increase in cell number was highest during the first 24 h following root initiation, and the cell cycle was extremely short with a very reduced G1 phase. Only the elongation zone of the mature adventitious root showed polyploidy.
An ultracytochemical study of nuclear bodies in meristematic plant cells (Cicer arietinum)
Authors: Luck B. T. , Lafontaine J.-G.
Published: April 2011

Plant cells are known to contain a variety of small spherical nuclear formations. Certain of these structures exhibit a loose fibrillar organization and have recently been shown from the examination of serial sections to represent centromeres. Such structures have so far only been observed in plant nuclei of the reticulate type. Other bodies described here appear to be true nuclear inclusions since, contrary to the centromeric formations just referred to, they are not associated with the chromatin reticulum. These spherules are often located close to the nucleolar surface and consist of a coarse filamentous component and of a pervading amorphous substance. Our various ultracytochemical observations reveal that the spherical bodies generally stain rather similarly to the fibrillar nucleolar regions. Judging from their reaction to ribonuclease and proteinase K, these nuclear inclusions contain mostly ribonucleoproteins. The presence of DNA within these bodies remains uncertain, and for this reason, it is suggested that they not be referred to as karyosomes, a term originally designating chromatin masses.
Étude au microscope électronique à balayage de la bulbille de Huperzia selago (L.) Bernh. (Lycopodium) : méristème apical, initiation foliaire et phyllotaxie
Authors: Vindt-Balguerie Emmeline
Published: April 2011

The shoot apex of the bulbil of Huperzia selago (L.) Bernh. (Lycopodium) has been examined by scanning electron microscope. From an ontogenic point of view, changes in shape and size have been observed in the apical meristem. Successive minimal and maximal areas of this meristem are described during a plastochron. Area and cell number are also quantified with the scanning electron microscope. Only one leaf is initiated at the beginning of each plastochron, and the two contact parastichies observed in the shoot apex of the mature bulbil are two foliar helices.
On the nonideality of chemostat operation using plant cell suspension cultures
Authors: Sahai O. P. , Shuler M. L.
Published: April 2011

Chemostats designed for continuous cultivation of plant cells, unlike traditional fermenters, generally use sparging alone for mixing. The residence times for cells and for surrounding medium are different under conditions of incomplete mixing. This paper identifies a mixing parameter, Ce/Cav (which is the exit cell concentration divided by the average cell concentration in the reactor), as a function of operational and system variables, airflow rate, nozzle diameter and placement, and concentration of cells for a chemostat of the design suggested by Wilson. When Ce/Cav is not equal to 1, traditional chemostat theory cannot be used. A correlation between specific growth rate μ, Ce/Cav, and dilution rate, D, has also been derived for the case of incomplete cellular mixing.
Parcours des faisceaux dans la tige adulte de Bryone (Bryonia dioica) (Cucurbitacées)
Authors: Courbet Henri
Published: April 2011

The growth of a young internode of Bryone stem stops whenever it is submitted to repeated rubbings. To assess if this is connected to the anatomy of the stem, the latter has been studied following dissection. Whatever their number, at each node two bundles end at the base of the leaf and six others form anastomoses. The vascularization of the tendril, of the lateral branch, and of the axis of the inflorescence is also described. The bundle course is not uniform and one can distinguish two different types. In the first type connections occur every two internodes. In the second type connections can be found every three internodes (10-bundle stem) or five internodes (14-bundle stem). The return of the bundles to the initial position is realised every seven nodes in stems having 10 bundles and every nine nodes in stems with 14 bundles. The number of bundles remains invariable in the same stem, but it varies in the different organs supported by the stem at the successive nodes. The growth inhibition at the node level is discussed in relation to the described anatomy. [Traduit par le journal]
Cold acclimation of wheat and smooth brome-grass cell suspensions
Authors: Chen P. M. , Gusta L. V.
Published: April 2011

Cell suspension cultures derived from spring wheat cv. Manitou (Triticum aestivum) and winter wheat cv. Kharkov tolerated freezing on agar media to −15 °C and −19 °C, respectively, after 10 days of acclimation at 4 °C without light. Cell water content decreased from 14 g H2O/g dry matter to 11 g H2O/g dry matter for both cultures during the hardening period. Cell viability following freezing was determined by both fluorescein diacetate vital-staining and regrowth procedures. The vital-staining technique was much quicker, simpler, and as accurate as the regrowth test. Cell suspension cultures derived from smooth brome-grass (Bromus inermis) readily acclimate to −20 °C either on agar media or as a cell suspension. Brome-grass cells washed prior to freezing with nutrient media minus sucrose were less hardy than cells washed with the nutrient media plus sucrose.
Dinitrogen fixation in Phaseolus vulgaris at low temperatures: interaction of temperature, growth stage, and time of inoculation
Authors: Rennie R. J. , Kemp G. A.
Published: April 2011

Nodulation and N2 fixation have not been reported in beans (Phaseolus vulgaris L.) below a temperature of 13 °C but, in southern Alberta, temperatures at planting may be as low as 10 °C. Two varieties of pea beans, 'Aurora' and 'Kentwood,' were inoculated at three growth stages (seeding, primary leaf horizontal, or first trifoliate leaf open) and grown at 10, 12, 14, or 16 °C. Nodulation and acetylene (C2H2) reduction occurred in both varieties at temperatures as low as 10 °C. At the lower temperatures, cold adaptability of the plant for early root growth determined the ability for nodulation and N2 fixation. At higher temperatures, plant-growth stage was a determining factor. 'Aurora' was superior to 'Kentwood' at 10 °C in nodulation, dry matter (DM), N yield, and N2 fixation because of its tolerance to low temperatures during early root growth. Inoculation with Rhizobium phaseoli at more advanced plant-growth stages decreased the time for nodulation at all four temperatures but resulted in higher yield and more N2 fixation in 'Aurora' only at 14 and 16 °C. At 10 °C, inoculation at seeding was more effective than at the other two growth stages for both varieties. Thus plant growth stages and growth temperature both determined the ability of a bean variety to support N2 fixation at various low temperatures.
Wild Aster lanceolatus × lateriflorus hybrids in Ontario and comments on the origin of A. ontarionis (Compositae–Astereae)
Authors: Semple John C. , Brammall Ronald A.
Published: April 2011

Chromosome numbers of putative wild Aster lanceolatus × lateriflorus hybrids were found to be either 2n = 40 or 2n = 48. A comparison of the morphology and chromosome numbers of the putative hybrids, their likely parental species, and A. ontarionis from Ontario revealed that the hybrids were morphologically and cytologically intermediate between A. lanceolatus and A. lateriflorus. The 2n = 40 hybrids were similar to A. ontarionis (2n = 32) but lacked the characteristic leaf pubescence of that species. At one site on the Bruce Peninsula 14 A. lanceolatus plants (2n = 64), 13 A. lateriflorus plants (2n = 32), and one hybrid (2n = 48) were collected and compared in detail. The hybrid was more like A. lanceolatus than the 2n = 40 hybrids from other sites where the A. lanceolatus parents were 2n = 48. The similarities between the putative hybrids and A. ontarionis suggest that this species arose via a hybridization event between A. lanceolatus and A. lateriflorus. Alternative origins are nonetheless possible and these along with the nomenclature of A. lanceolatus are reviewed.
Ultrastructural and developmental alterations induced by Periconia circinata toxin in the root tip of sorghum
Authors: Arias Jonathan A. , Dunkle Larry D. , Bracker Charles E.
Published: April 2011

Cytological and developmental effects induced by Periconia circinata toxin were examined to better understand the mechanism of action for this toxin. Roots of sorghum seedlings susceptible and resistant to P. circinata were incubated in 500 ng toxin/mL (treated) or water (controls). Root cap cells of resistant seedlings treated with the toxin were cytologically similar to those of controls, although the toxin caused a transient inhibition of mitosis in cells of the primary root tip. In outer root cap cells of susceptible seedlings treated for 0.25 h, hypersecretory activity was lost, secretory vesicles were fewer, and secretory product accumulated between the plasma membrane and cell wall. Also, inner root cap cells showed increased vacuolation. Longer treatments caused increased vacuolation, loss of starch, increased numbers of lipid bodies, pleomorphic amyloplasts, regularly stacked endoplasmic reticulum, apparent changes in the amounts of cytomembranes, dispersion of heterochromatin, and autolysis. Mitochondrial morphology was normal, but lesions in the tonoplast occurred before autolysis. The toxin also inhibited expansion and sloughing off of root cap cells and mitotic activity in the root tip. Stacked endoplasmic reticulum, nonhypersecretory dictyosomes, fewer secretory vesicles, increased vacuolation, reorganization of heterochromatin, and increased secretory product outside the protoplast were induced by P. circinata toxin and by cyanide. These data suggested that a cyanogenic compound is biologically active in cells treated with P. circinata toxin. Our results suggest that the toxin transiently affects resistant seedlings and in susceptible seedlings alters vacuolar expansion, secretory activity, and endomembrane flow, although other processes may also be affected.
The pollination biology and breeding system of Aplectrum hyemale (Orchidaceae)
Authors: Hogan Kevin P.
Published: April 2011

The pollination biology of Aplectrum hyemale (Orchidaceae) in Brownfield Woods and in Trelease Woods, east central Illinois, was studied in May 1981. During 26 h of observation over the 4-day flowering period the only potential pollinators observed entering flowers were Dialictus oblongus (Hymenoptera: Halictidae). Five bees of this species were seen entering flowers; none could be seen to be carrying pollinia at any time. In spite of the low visitation rates fruit-set was 82.1% in unmanipulated flowers. Fruit-set in bagged, unmanipulated flowers was 70.6%, indicating that autogamy occurs in this species. Fruit-set in bagged, emasculated flowers was 47.1%, which suggests that agamospermy may occur. Fruit-set was 92.5% in hand-pollinated flowers. No significant differences were found between treatments in seed weight or in percent seed viability. Autogamy and (or) agamospermy, along with possible clonal growth, are consistent with previously published reports of low levels of variability in this species.
The effect of population structure on growth patterns in the woody goldenrod Solidago pauciflosculosa
Authors: Pritts Marvin P. , Hancock James F.
Published: April 2011

The population structure and growth patterns of two populations of Solidago pauciflosculosa, a woody goldenrod, were investigated. Populations consisted of even-aged contagious patches of individuals, a dispersion pattern likely caused by the periodic appearance of microsites suitable for seedling establishment. The density of individuals within the even-aged clumps varied considerably and was correlated with total plant biomass and reproductive output. Density was not correlated with either reproductive or nonreproductive allocation patterns.
L'influence de la carence en pyridoxine sur la morphologie et l'ultrastructure cellulaire de Ceratocystis ulmi
Authors: Dalpé Y.
Published: April 2011

Deficiency in pyridoxine of a synthetic medium induces yeastlike growth of Ceratocystis ulmi. The addition of pyridoxine allows the organism, incubated 1 to 12 days in the absence of the vitamin, to recover in 24 h its filamentous growth morphology. The comparative study of the ultrastructure of mycelial and yeast cells reveals for the latter a thickening of the cell wall, a quantitative cytoplasmic impoverishment in endoplasmic reticulum and ribosomes, and an accumulation of lipidic and osmiophilic bodies.
Vegetation patterns in the North Black River peatland, northern Minnesota
Authors: Glaser Paul H.
Published: April 2011

Raised bogs and water tracks in the 193-km2 North Black River peatland in northern Minnesota were examined in relation to the vegetation, water chemistry, and surficial water movements as inferred from infrared aerial photographs, LANDSAT imagery, and orthophoto topographic maps. Two noda of bog vegetation were distinguished by the Braun–Blanquet system; both bog noda are associated with relatively dilute, acidic waters (pH range 3.9–4.1; Ca2+ concentration range 0.6–1.6 mg L−1; specific conductivity, Kcorr range 1.3–83 μS cm−1). Rich-fen vegetation in contrast is more variable within this peatland and generally occurs in water tracks with a correspondingly wide range of pH (range 5.0–6.2), Ca2+ concentration (range 3.6–30.4 mg L−1), and Kcorr (range 31 to 182 μS cm−1). Poor-fen vegetation was most distinguishable by the transitional nature of its vegetation and water chemistry with at least a few minerotrophic indicator species present in all cases and intermediate ranges in pH (3.7–5.2), Ca2+ concentration (0.6–5.5 mg L−1), and Kcorr (16–72 μS cm−1). Bog and fen patterns in this peatland are consistently related to topographic features along the upland crest of each peatland watershed, indicating that topography controls the path of minerotrophic runoff draining onto the peatland, and thus creating zones with either enriched minerotrophic flow (in which water tracks develop) or stagnation zones (where bogs develop) on the peatland downslope.
Vesicular–arbuscular mycorrhizal fungi associated with native tall grass prairie and cultivated winter wheat
Authors: Hetrick B. A. Daniels , Bloom J.
Published: April 2011

More vesicular–arbuscular mycorrhizal (VAM) fungal species and significantly more fungal spores were recovered from undisturbed prairie soils than four winter wheat field soils in Kansas through the 1980–1981 growing season. Two previously undescribed sporocarpic species of Endogonaceae were found in prairie samples but have not been successfully established in pot culture, leaving the genus to which they belong unclear. Though variable, 11–50% VAM root colonization was evident in all prairie grass roots sampled throughout the year. In contrast, no identifiable VAM root colonization was evident in wheat until May after flowering when 27% root colonization was observed. During the 1981–1982 growing season, roots of two other wheat fields were sampled with similar results. No colonization occurred until May when 8% root colonization was evident. The possible influence of such low levels of root colonization occurring quite late in the growing season of winter wheat is discussed.
Phenotypic differences in the seasonal pattern of net photosynthesis in Cladonia stellaris
Authors: Kershaw K. A. , MacFarlane J. D. , Webber M. R. , Fovargue A.
Published: April 2011

Despite the contrasting thermal and light environment of sun and shade ecotypes of Cladonia stellaris, analysis of the pattern of net photosynthesis throughout the year as well as enzyme polymorphism in each morphotype has found little genotypic difference. The large disparity between photosynthetic capacity in the sun and shade replicates is shown to be due to a difference in chlorophyll content. There is a significant decline in photosynthetic capacity in November and this is shown to be reversible uncoupling of energy transduction in some photosynthetic units during the winter period. The control of coupling and uncoupling of photosynthetic units is found to be mediated by both day length and thallus temperature and a double environmental signal in June and July of short days coupled to low temperature will initiate and finalize the event within 12 h. This response pattern is discussed in relation to identical capacity changes in other lichen species. Apart from a single isoenzyme difference in esterase polymorphism, no differences in the zymograms of leucine aminopeptidase, phosphoglucoisomerase, or acid phosphatase were detected and this overall genetic homogeneity was equally evident in a general protein gel. This unexpected degree of homogeneity is discussed in terms of the difficulties in assessing enzyme polymorphisms in different plant populations, without maximum refinement of protein preparation methods and electrophoretic techniques. It is concluded that the two quite distinct sun and shade morphotypes only reflect phenotypic differences. In contrast, however, significant differences are reported in the distribution of specific enzymes between the tops and bases of the podetia.
Morphological, cytological, and flavonoid variability of the Arnica angustifolia aggregate (Asteraceae)
Authors: Downie Stephen R.
Published: April 2011

The Arnica angustifolia aggregate is a circumpolar taxon previously consisting of a number of geographically distinct infra-specific taxa. Cluster and principal component analyses of 99 populations revealed the aggregate to be best represented by two subspecies: A. angustifolia subsp. angustifolia (a combination of the previously recognized subspecies angustifolia, attenuata, sornborgeri, intermedia, iljinii, and alpina and A. plantaginea) and A. angustifolia subsp. tomentosa. Arnica angustifolia subsp. angustifolia is polymorphic and varied in ploidy level and foliar flavonoid chemistry. No significant differences were found among the means of 14 characters in plants collected from six broadly delimited geographic areas. Four cytotypes (2n = 38, 57, 76, and 95) and seven flavonoid glycosides (five flavonols and two flavones) were discerned. The aggregate is predominantly agamospermous with amphimictic phases in unglaciated Alaska and west central Yukon. Disjunct distributions are probably the result of survival in refugia during the late Wisconsinan.
Effets d'une plasmolyse prolongée sur les tubes polliniques angiospermiens en culture in vitro : étude ultrastructurale
Authors: Pargney Jean-Claude
Published: April 2011

In angiosperm plants subjected to plasmolysis, pollen tubes may undergo substantial ultrastructural changes accompanied by a gradual deterioration of those processes involved in cell syntheses. However, some tubes quickly regenerate a polysaccharide wall and thus ensure their extension. Others undergo fragmentation of their cytoplasm and a serious breakdown in processes involved in cell wall synthesis. In these extreme cases, the endoplasmic reticulum is the only compartment that is readily discernible.
Phenetic relationships in the Festuca spp. from Patagonia
Authors: Dubcovsky Jorge , Martínez Arturo
Published: April 2011

Forty-two anatomical and exomorphological characters from 16 species and 2 varieties of Festuca native from Patagonia were numerically analyzed. Principal components analysis together with cluster analysis arranged 14 taxa into 5 groups (F. tunicata and F. acanthophylla, group 1; F. monticola, F. thermarum, and F. scabriuscula, group 2; F. pallescens, F. p. var. scabra, and F. kurtziana, group 3; F. gracillima and F. ventanicola, group 4; and F. contracta, F. rubra var. simpliciuscula, F. pyrogea, and F. magellanica, group 5; F. argentina, F. purpurascens, F. cirrosa and F. pampeana were not included in any of the groups). Cluster analyses performed on either vegetative or reproductive characters showed that they alone are not enough to summarize variation among these taxa.
Genera coelomycetum. XXIV. Chithramia anamorph gen.nov.
Authors: Raj T. R. Nag
Published: April 2011

A new anamorph genus Chithramia, is proposed to accommodate a coelomycete with appendaged conidia in which the appendages are formed in a manner unique among the coelomycetes. The fungus was collected on rice (Oryza sativa) in India.
Response of highbush blueberry seed germination to gibberellin A3 and 6N-benzyladenine
Authors: Dweikat I. M. , Lyrene P. M.
Published: April 2011

Open-pollinated highbush blueberry (Vaccinium corymbosum L.) seeds were treated with 0, 2.6, 5.2, 10.4, or 20.8 mM gibberellic acid, 0, 0.4, 2.2, or 4.4 mM 6N-benzyladenine, or the two growth regulators in combination. Seeds were treated for 24 h, then germinated under intermittent mist during summer with temperatures fluctuating between 21 and 40 °C. Germinated seeds were counted weekly from day 15 to day 30, using hypocotyl exposure to indicate germination. Treatment with gibberellic acid at 10.4 mM in combination with 6N-benzyladenine at 0.4 to 2.2 mM gave the highest germination percentage. The relationship between gibberellic acid concentration and seed germination was cubic. Seedlings from the germinated seed flowered and fruited the following spring, making it possible for highbush blueberry to complete a generation in 1 year.
Acide, 2,3,5-triiodobenzoïque (TIBA) et initiation foliare chez Lycopersicon esculentum
Authors: Hernández Mercédes Niebla , Driss-École Dominique
Published: April 2011

In Lycopersicon esculentum, treatment with 2,3,5-triiodobenzoic acid is followed by a stop in leaf initiation and the building of an aphyllous structure. However, the setting of provascular cells is maintained in this new structure, as well as the differentiation of the internal and external phloem, but xylem differentiation does not occur. Therefore, the differentiation of the provascular elements is independent of the localized phenomenon of leaf initiation. Only 10% of the treated plants recover their phyllotaxic activity after 2,3,5-triiodobenzoic is removed. The new leaves are formed following the spiral direction of the underlying foliar helices and the vessels differentiate only with the initiation of these new leaves. The first leaf newly erected is not in the extension of the underlying foliar helix on which it should be, but the recovery of the leaf initiation occurs in the next generative center. The new leaf always appears at the same place relative to the subjacent leaves, which supports the theory of an acropetal stimulus of leaf initiation.
Variation in phytolith assemblages within a population of corn (cv. Mandan Yellow Flour)
Authors: Mulholland Susan C. , Rapp Jr. George , Ollendorf Amy L. , Regal Ronald
Published: April 2011

This project investigates the effects of leaf side, leaf position, individual plant, and hill (or plant group) on phytolith assemblages from Zea mays L. cultivar Mandan Yellow Flour. Thirty-two samples were examined, and 200 phytoliths were classified from each sample. Statistical analysis indicates that leaf side is significant at the 0.05 level above random counting variation; leaf position, individual plant, and hill are not generally significant beyond the effect of leaf side. Analysis of a single sample, either a half or entire leaf, is not sufficient for compilation of representative phytolith assemblages from a plant population. Phytolith reference collections should not be based on single samples of each species. Multiple samples from a population need to be analyzed to obtain information on assemblage variation within the population. The variation of corn phytolith assemblages in this study overlaps those of many Panicoid grasses, indicating that additional morphological characters need to be identified to distinguish corn from wild grasses in the Great Plains. Key words: phytoliths, corn, frequencies, variation.
De l'utilisation du lanthane comme traceur de la voie apoplastique chez Cystoseira nodicaulis (Fucales, Cystoseiraceae)
Authors: Pellegrini Liliane , Epiard-Lahaye Marie , Penot Michel
Published: April 2011

Lanthanum was used as an electron-dense marker of apoplastic transport in the brown alga Cystoseira nodicaulis. A lanthanum salt, La(NO3)3, was given in seawater at the base of excised branches for 2–8 days. Lanthanum transport into two regions distant from the point of application, the base and apex of the branches, was followed over time by electron microscopy. Restricted localisation of the deposits confirmed that an apoplastic pathway exists in this alga. The kinetics of transport are slow. Dense deposits were located exclusively in the cell walls of meristoderm and cortex cells. The significance of apoplastic transport in algae is discussed in the context of long-distance transport. The existence of an apoplastic route does not exclude the occurrence of symplasmic transport, which is suggested by the numerous plasmodesmata present in the medulla. Key words: algae, apoplast, Cystoseira, lanthanum, long-distance transport.
A field and literature survey, with interpretation, of elemental concentrations in blueberry (Vaccinium angustifolium)
Authors: Sheppard S. C.
Published: April 2011

Blueberry species are important for assessment of pollutant impacts in boreal settings because they are effective colonizers of disturbed sites, are tolerant of high levels of certain heavy metals, and are an attractive food for humans. To investigate patterns in its accumulation of elements and to provide background data, the concentrations of Al, B, Ba, Br, Ca, Ce, Cl, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Si, Sr, Ti, Zn, and Zr were measured in leaves of Vaccinium angustifolium Ait. collected at 64 sites across much of the species range in Canada. These included both cultivated and natural populations. Ranges for 24 other elements in Vaccinium species have been compiled from the literature. Measurements of site and soil characteristics were made for the 64 sites to investigate their effects on concentrations in leaves. The concentration data were right-skewed, and this has implications for both data analysis and environmental impact assessment. The concentrations of most elements were positively correlated, and this was related to soil organic matter content and other soil properties. Plant concentrations were only weakly related to soil concentrations. Plant height was positively correlated to soil pH and leaf Ca, opposite to the expected trend. Overall, about half of the variation in plant concentrations was related to site-to-site variation; with the exception of Ni and Mg levels around Sudbury, Ontario, there was little indication of spatial grouping. The data indicate a relatively homogeneous elemental composition of V. angustifolium across the range sampled and between cultivated and natural populations. Key words: metals, nutrient, background, impact, pollutant.
Chemical composition of seed saponins as a guide to the classification of Medicago species
Authors: Jurzysta M. , Burda S. , Oleszek W. , Ploszynski M. , Small E. , Nozzolillo C.
Published: April 2011

The presence of saponins and their aglycones (sapogenins) was surveyed in seeds of 33 species of Medicago (Fabaceae). The four major subsections of the largest taxonomic section of Medicago, section Spirocarpos, can generally be distinguished by presence and (or) absence of medicagenic acid and zanhic acid. The latter sapogenin was found only in three of the subsections of Spirocarpos and seems to reflect the phylogenetic recency of these groups within Medicago. The distribution of zanhic acid in combination with other considerations proved useful in establishing that Medicago granadensis seems to be the oldest species in subsection Intertextae. The saponin profile of Medicago hybrida, most recently assigned to section Medicago, strongly supports the placement of this species and its relative Medicago sufruticosa in a separate section. Hemolytic saponins proved to be much more common in those species of Medicago that retain their seeds permanently within the fruit compared with species that tend to scatter their seeds, possibly because the former can benefit more from the antiherbivorous and (or) allelopathic properties of the saponins. Key words: hemolytic saponins, chemotaxonomy, taxonomy, ecology, Medicago.
Development of open and closed leaf sheaths in Festuca trachyphylla and Festuca rubra (Poaceae)
Authors: Liu Youqi , Dengler Nancy G.
Published: April 2011

The development of the leaf sheaths in two species of Festuca, subgenus Festuca, Festuca trachyphylla (Hackel) Krajina with open leaf sheaths and Festuca rubra L. s.l. with closed leaf sheaths is compared to determine the developmental basis of this taxonomically important character. In both species serial cross sections of seedlings, scanning electron microscopy, and dissections of whole plants showed that a short tubular leaf base is formed early during the second plastochron of leaf development. Later during the same plastochron, ligule formation delimits sheath and blade; at this stage, the tubular portion occupies about one-half (200 – 500 μm) of the incipient leaf sheath. Differential extension growth of the distal open portion and proximal closed section of the sheath results in the primarily open or closed sheaths that characterize the mature leaves of the two species. The longitudinal splitting of the tubular leaf sheath in a position opposite the midvein in F. rubra is anticipated by a zone of small-diameter cells within the ground tissue, but no other structural correlates of sheath mechanical strength and persistence were detected. Our observations indicate that subtle shifts in the distribution of growth during leaf expansion result in the contrasting character states exemplified by these two species. Key words: Festuca, grass leaf development, leaf sheath, Poaceae.
High-frequency direct somatic embryogenesis in thin layer cultures of hybrid seed geranium (Pelargonium ×hortorum)
Authors: Gill Ravinder , Gerrath Jean M. , Saxena Praveen K.
Published: April 2011

Thin layer explants from the hypocotyls of young seedlings of geranium (Pelargonium ×hortorum Bailey) produced somatic embryos in response to thidiazuron (TDZ) or a combination of indoleacetic acid and N6-benzylaminopurine, but the number of embryos was much less in the latter than with TDZ. The development of somatic embryos in cultures of thin layers was rapid and the number of embryos was about eightfold higher than in cultures of whole hypocotyl explants. Thin layer explants of 1-week-old seedlings produced a high number of somatic embryos than those obtained from older seedlings. The cultivar Scarlet Orbit Improved showed better regeneration potential than 'Sprinter Scarlet'. There were no visible differences in total number of somatic embryos produced in the medium containing sucrose or glucose. The addition of glutamine to the induction medium further improved the number of somatic embryos that developed. Regenerated somatic embryos developed into complete plantlets within 6 to 8 weeks of culture initiation. Key words: Pelargonium ×hortorum, geranium, somatic embryogenesis, thin layers, thidiazuron.
Control of plant frequency on an environmental gradient: effects of abiotic variables, neighbours, and predators on Poa pratensis and Poa compressa (Gramineae)
Authors: Reader R. J. , Bonser S. P.
Published: April 2011

Effects of abiotic variables, neighbours, and predators on seedling establishment and tiller production of two perennial grasses (Poa pratensis L. and Poa compressa L.) were determined on a topographic gradient in an abandoned pasture. Seeds and plants of each species were added to experimental plots set up both at the top (ridges) and bottoms (hollows) of hills. Seedling establishment and tiller number per plant were each compared where seeds (or plants) were exposed to abiotic variables with and without the presence of neighbours and (or) predators. For P. pratensis, which occurred naturally more often in hollows than on ridges, abiotic variation appeared to be most important in controlling its frequency on the gradient. Tiller production was significantly lower on ridges than in hollows where plants were exposed only to abiotic variables (i.e., neighbours removed and predators excluded). For P. compressa, which occurred naturally less often in hollows than on ridges, greater suppression of seedling emergence by neighbours in hollows than on ridges appeared to be the factor controlling its frequency on the gradient. These results provide support for the view that variation in plant frequency across an environmental gradient reflects abiotic variation and differential effects of neighbours. Key words: competition, predation, abiotic stress, Poa, environmental gradient.
Mating system of Racosperma auriculiforme in a seed production area in Zaire
Authors: Khasa P. Damase , Cheliak William M. , Bousquet Jean
Published: April 2011

Analysis of the mating system of Racosperma auriculiforme (formerly Acacia auriculiformis) in a seed production area in Zaire was conducted using a mixed mating model at five polymorphic loci (Est-2, Est-3, G6p-dh, Nadhdh-2, Pgm-1). Single-locus estimates of outcrossing rate varied widely between 0.615 and 1.204 and were significantly heterogenous among and within the stands. Weighted means of single-locus estimates of outcrossing rates (ts) ranged from 0.859 to 1.032 while multilocus estimates of outcrossing rates (tm) ranged from 0.863 to 1.059. Comparisons between the single-locus estimates and the multilocus estimates of outcrossing rates indicated that most of the inbreeding detected was due to consanguineous (sibling) matings rather than selfing. Comparisons of observed and expected inbreeding coefficients indicated a general deficit of heterozygotes over the frequencies expected from random mating in the single stands and the pooled stands. Locus to locus variation in outcrossing rates suggested that violation of the mixed mating model might have occurred. Implications for seed production, collection, and distribution for reforestation are discussed. Key words: Acacia, mating system, Racosperma, seed production area, Zaire.
Comparison of size-dependent reproductive effort in two dandelion (Taraxacum officinale) populations
Authors: Welham Clive VJ , Setter Robert A
Published: April 2011

Reproductive effort in dandelions (Taraxacum officinale Weber) from two different habitats was compared. One dandelion population occupied a 5-year-old alfalfa (Medicago spp.) field, an environment subject to regular disturbance but with a relatively low density of neighbours. Individuals from the second population were derived from a number of undisturbed sites where the density of neighbouring grasses was high. Three hypotheses were evaluated with respect to the observed patterns of reproductive effort. One hypothesis, that reproductive effort was a function of differences between habitats in resource availability, did not provide an explanation for our results. A second hypothesis considered patterns of reproductive effort when mortality rates varied with degree of disturbance and neighbour density, which was a consequence of each habitat representing a different successional environment. A third hypothesis used a life-history approach to predict reproductive effort when mortality schedules were size dependent. Both of these hypotheses received support for their predictions. There was more than a sixfold variation in reproductive effort among individuals from the alfalfa field and a fourfold variation on the undisturbed sites. Much of this variation, however, was attributable to a size-dependent relationship between reproductive effort and vegetative mass. Total reproductive effort (total seed plus scape mass) in both populations increased linearly with vegetative mass, but the slope for the population from the alfalfa field was significantly higher. In contrast, proportional reproductive effort (total seed plus scape mass per vegetative mass) showed a curvilinear increase for the alfalfa field population but was linear and negative for the undisturbed population. There were also important differences between the populations in reproductive morphology. Larger plants on the alfalfa field had longer average scape lengths, produced more flower heads (capitula) per plant, had greater seed production, and had a lower ratio of seed mass per pappus area; only mean scape and mean seed mass did not differ significantly. We suggest that dandelions on the alfalfa field have a different reproductive morphology to facilitate colonization of open areas on the field.Key words: Taraxacum, dandelion, reproductive effort, biomass, life history, neighbour density, agriculture, weed.
Morphological observations of Aulacoseira using scanning electron microscopy
Authors: Siver Peter A. , Kling Hedy
Published: April 2011

Despite the fact that the genus Aulacoseira Thwaites is a common component of phytoplankton communities in many North American water bodies, there are relatively few taxonomic based surveys utilizing the scanning electron microscope (SEM). In addition, based on the current literature, some species are difficult to identify or distinguish from other taxa. We present taxonomic and morphological observations on 19 taxa based primarily on collections made in Connecticut, U.S.A., and from central and northern Canada. Aulacoseira ambigua (Grunow) Simonsen, Aulacoseira subarctica (O. Müller) Haworth, and Aulacoseira tenella (Nygaard) Simonsen were the most common species encountered in Connecticut, while Aulacoseira islandica (O. Müller) Simonsen, Aulacoseira granulata (Ehrenberg) Simonsen, A. subarctica, and A. ambigua were the dominant species from many central Canada localities. In the Canadian Shield region, specimens of the Aulacoseira disions (Ehrenberg) Simonsen group, the Aulacoseira lirata (Ehrenberg) Ross in Hartley group, and Aulacoseira perglabra (Oestrup) Haworth were more common. We had the most difficulty identifying taxa in the A. distorts and A. perglabra complexes and distinguishing A. lirata from Aulacoseira alpigena (Grunow) Krammer. The primary objectives of the paper were to provide an additional source of high-resolution SEM micrographs for many of the more common species of Aulacoseira, comment on the morphological detail of each taxon, and to discuss the difficulties we encountered using the current literature to identify some of the species. A few ecological observations are also provided. Lastly, we propose two new combinations, Aulacoseira pseudoamericana (Camburn) comb.nov. and Aulacoseira distans var. nivaloides (Camburn) comb.nov. Key words: diatoms, Aulacoseira, North America, taxonomy, morphology.
Seasonal variation in dormancy and light sensitivity in buried seeds of eight annual weed species
Authors: Milberg Per , Andersson Lars
Published: April 2011

We recorded germination in three different light environments (light, dark, and after a short light exposure) in eight annual weed species. Seeds were buried outdoors at the end of November 1994 and exhumed monthly from March 1995 to April 1996. All species exhibited substantial seasonal changes in dormancy level, and the patterns suggest that seeds of Papaver rhoeas germinate strictly in the autumn; Capsella bursa-pastoris, Descurainia sophia, Spergula arvensis, and Urtica urens mainly in the autumn; Chenopodium suecicum strictly in the spring; and Matricaria perforata mainly in the spring. Lapsana communis showed inconsistent dormancy changes over the year. All species had acquired a light requirement for germination after being in the soil, and in many cases the short light exposure (1050 μmol∙m−2) was enough to fulfil this requirement. The demonstrated seasonal changes in light sensitivity in several of the species will have to be taken into account in attempts to photocontrol weeds. By using the short-light treatment, we were able to detect seasonal dormancy changes that would not have been obvious by testing for germination in only light and darkness. Hence, light is not a simple dichotomous factor in its effect on germination. Key words: dormancy, germination, light, seed, Sweden, weed.
Endophytic fungi in leaves of ericaceous plants
Authors: Okane I , Nakagiri A , Ito T
Published: April 2011

Endophytic fungal assemblages were investigated in different leaf stages of eight species of Ericaceae (six species of Rhododendron, Enkianthus perulatus, and Pieris japonica). Guignardia sp. (anamorph: Phyllosticta sp.), Phomopsis sp., and Colletotrichum gloeosporioides were found in the leaves of all plants. The frequency of Guignardia sp. was highest in senescent leaves, while in young leaves it was lower than those of Phomopsis sp., and C. gloeosporioides. Discostroma tricellulare was isolated in high frequency from the leaves of Rhododendron obtusum. The colonization frequencies of these endophytic fungi on fallen leaves decreased as the leaves became old, while those of Pestalotiopsis, Alternaria, and others increased after the leaves fell. No significant differences were found among the compositions of endophytic fungal assemblages on ericaceous plants at the site investigated. It was considered that the endophytic fungi infect young leaves and remain latent in the leaves without producing symptoms while the hosts are physiologically active. Discostroma tricellulare was considered to be specific for R. obtusum. The colonization frequencies of the endophytic fungi were clearly lower on the leaves of P. japonica than on those of the other plants. It is considered that asebotoxin, which is known to be toxic to animals and insects, and other secondary metabolites retard fungal invasion in P. japonica.Key words: endophytic fungi, ericaceous plants, fungal succession.
The additional stamens of flo10-1 mutants of Arabidopsis thaliana are compromised in production and viability of pollen
Authors: Pylatuik Jeffrey D , Bonham-Smith Peta C , Davis Arthur R
Published: April 2011

flo10-1 (superman-2) is a floral mutant in Arabidopsis thaliana that normally produces female sterile flowers. This phenotypic aberration results from a combination of increased stamen number and reduced or abnormal carpels that are nonfunctional. The flowers of flo10-1 contain two lateral and four median stamens, as seen in wild-type plants; however, they also contain several additional stamens. All stamen types have been examined with respect to frequency and location within the flower. The amount of pollen produced from each of the three types of stamens of flo10-1 and the viability of this pollen were also examined and compared with wild-type (cv. Columbia) to determine the consequences of this mutation on male fertility. Both the lateral and median stamens of flo10-1 and wild-type plants produced similar amounts of pollen per stamen and demonstrated no significant difference in viability. Per stamen, the additionals of flo10-1 produced significantly less pollen than those of the laterals and medians. Furthermore, the pollen produced from these additional stamens was significantly less viable. Although less abundant and viable, pollen produced by additional stamens can effectively fertilize ovules, producing normal, healthy plants.Key words: pollen (viability, production), stamen, male fertility, flower development, Arabidopsis thaliana, flo10-1.