bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogenetic relationships and infraspecific variation in Canadian Arctic Poa based on chloroplast DNA restriction site data
Authors: Gillespie Lynn J , Boles Ruben
Published: April 2011

Infraspecific variation and phylogenetic relationships of Canadian Arctic species of the genus Poa were studied based on chloroplast DNA (cpDNA) variation. Restriction site analysis of polymerase chain reaction amplified cpDNA was used to reexamine the status of infraspecific taxa, reconstruct phylogenetic relationships, and reexamine previous classification systems and hypotheses of relationships. Infraspecific variation was detected in three species, but only in Poa hartzii Gand. did it correspond to infraspecific taxa where recognition of subspecies ammophila at the species level is supported. Additional variation in P. hartzii ssp. hartzii is hypothesized to be the result of hybridization with Poa glauca in the High Arctic and subsequent introgression resulting in repeated transfer of P. glauca DNA. The variation in Poa pratensis L. had a geographical rather than taxonomic basis, and is hypothesized to correspond to indigenous arctic versus introduced extra-arctic populations. In P. glauca Vahl cpDNA variation was detected only in western Low Arctic and boreal populations and may represent greater variation where the species survived the Pleistocene glaciations. Cladistic parsimony analysis of cpDNA restriction site data mostly confirms recent infrageneric classification systems. Poa alpina L., along with the non-arctic Poa annua L. and Poa sect. Sylvestres, formed the basalmost clades. The remaining taxa group into two main clades: one consisting of Poa sects. Poa, Homalopoa, Madropoa and Diocopoa; the second, of Poa sects. Secundae, Pandemos, Abbreviatae and Stenopoa. Poa sect. Poa, comprising Poa arctica R. Br. and P. pratensis, is a strongly supported monophyletic group, not closely related to P. alpina. Poa hartzii is confirmed as a member of a paraphyletic or weakly supported P. sect. Secundae. Poa glauca and Poa abbreviata R. Br. are distinct members within a generally unresolved Poa. sect. Stenopoa-Abbreviatae complexKey words: Poa, Canadian arctic, chloroplast DNA, restriction site analysis, infraspecific variation, phylogeny.
Scutellospora crenulata, a new species of Glomales from La Gran Sabana, Venezuela
Authors: Herrera-Peraza Ricardo A , Cuenca Gisela , Walker Christopher
Published: April 2011

A newly discovered glomalean fungus, Scutellospora crenulata, is described and illustrated. This species possesses a complex spore ornamentation composed of dome-like sub-polygonal papillae partly separated by pits. The presence of a "beaded" spore wall component is reported for the first time in a member of Gigasporaceae.Key words: arbuscular mycorrhizal fungus, Gigasporaceae, tropical soil, sclerophyllous shrubland.
A survey of the presence and morphology of orbicules in European allergenic angiosperms. Background information for allergen research
Authors: Vinckier Stefan , Smets Erik
Published: April 2011

Allergenic activity in the atmospheric aerosol of small particles in the size range of a few micrometres or less may play an important role in causing allergic reactions in the lower regions of the lungs, often seen in pollinosis. Orbicules (= Ubisch bodies) are small, mostly spherical granules of sporopollenin, which can occur on the radial and innermost tangential wall of secretory tapetum cells. In instances where orbicules of allergenic species are dispersed into the atmosphere, they may act as effective vectors of allergens. We investigated the presence and morphology of orbicules in 15 allergenic species using scanning electron microscopy. Orbicules were present in all species investigated of the families Betulaceae, Chenopodiaceae, Fagaceae, Poaceae, Polygonaceae, and Urticaceae. In the species of the Asteraceae and Oleaceae studied, orbicules were lacking. Almost all orbicules observed were spiny. Their mean diameters range from 0.342 to 1.130 μm. Orbicules can be part of the fraction of small particles in the size range of a few micrometres or less, emitted from the anthers. Our results clearly indicate that a thorough investigation of the sites of allergens across the whole anther is required to reveal whether or not these orbicules possess allergens.Key words: allergenic plants, allergen research, morphology, orbicules.
Sexual demographics of riparian populations of Populus deltoides: Can mortality be predicted from a change in reproductive status?
Authors: Rowland Diane L , Johnson Nancy C
Published: April 2011

Populus deltoides var. wislizenii (S. Wats.) Eckenwalder (cottonwood) forests along the Rio Grande drainage are predicted to disappear within this century. We evaluated stand health over 3 years by examining the sex ratio, size, and spatial distribution of male, female, and nonreproductive trees in six even-aged stands of P. deltoides spanning 280 km along the Rio Grande drainage. There was no evidence of biased sex ratios or spatial segregation of sexes; however, tree mortality was strongly related to reproductive status. In the most stressed population, over half of the mature trees remained nonreproductive and a substantial number switched from reproductive to nonreproductive status. Logistic regression revealed that over all populations, tree size, reproductive status in previous years, and population were significant factors affecting reproduction. By considering physiological and environmental differences, we determined two groups of nonreproductive individuals: those previously reproductive that became nonreproductive and those that remained nonreproductive over the 3 years. The former group appeared to be under greater physiological and environmental stress. Monitoring the rate at which individuals change reproductive status provides an effective and simple measurement that can predict survival of riparian cottonwood populations.Key Words: Populus deltoides, sex ratio, Rio Grande basin, reproductive status, nonreproductive.
Genetic structure of yellow cedar (Chamaecyparis nootkatensis)
Authors: Ritland Carol , Pape Terry , Ritland Kermit
Published: April 2011

A range-wide survey of isozyme variation in yellow cedar (Chamaecyparis nootkatensis (D. Don) Spach; or Alaska cedar) found significant inbreeding and a striking geographical structure. The proportion of diversity among populations (GST) was 0.139, and three major geographical groups were evident: (1) Vancouver Island - mid-north coast British Columbia (B.C.); (2) south coast B.C. - Washington state; (3) southeast Alaska. This may indicate the presence of multiple refugia during ice-age range contractions. Geographically disjunct populations in Oregon and southeastern B.C. were also genetically distinct. Adult inbreeding coefficients (F) were usually positive but varied widely among populations, as did gene diversity. The overall average of F = 0.18 suggests that considerable selfing (ca. 30%) occurs in this species. Other statistics were more typical for a conifer: within population heterozygosity (HS) averaged 0.148, total gene diversity (HT) was 0.171, and the number of alleles per locus and percentage polymorphic loci averaged 1.68 and 50, respectively. This geographic structure has implications for species conservation and for breeding programs. Also, previous studies of other Cupressoideae (Rich. ex Sweet) species indicate that these levels of inbreeding and population structure are not uncommon, and may influence evolutionary divergence in the Cupressoideae.Key words: Chamaecyparis nootkatensis, yellow cedar, genetic structure, inbreeding, phylogeography, isozymes.
Induced resistance and control of charcoal rot in Cicer arietinum (chickpea) by Pseudomonas fluorescens
Authors: Srivastava Alok K , Singh Tanuja , Jana T K , Arora Dilip K
Published: April 2011

Pseudomonas fluorescens isolate 4-92 induced systemic resistance against charcoal rot disease in chickpea (Cicer arietinum L.) caused by Macrophomina phaseolina (Tassi) Goidanich. Time-course accumulation of pathogenesis-related (PR) proteins (chitinases and glucanases) in chickpea plants inoculated with P. fluorescens was significantly (P = 0.05) higher than in control plants. The level of chitinases and glucanases increased by 6.6- to 7-fold up to 4 days postinoculation; thereafter, little decrease in the activity of PR proteins was observed. Root-colonizing populations of P. fluorescens were at a maximum 2 days after transplantation at different inoculum concentrations, and decreased over time. Inoculation of root tips of chickpea by P. fluorescens, 2,6-dichloroisonicotinic acid, and o-acetylsalicylic acid induced systemic resistance against charcoal rot. Disease was 33 to 55.5% higher in control plants than in plants inoculated with chemical inducers or P. fluorescens. Single treatment of plants with P. fluorescens increased disease resistance by 33%, whereas combined application of P. fluorescens with either of the chemical inducers was most effective in inducing the resistance by 2- to 2.25-fold. The time-course study shows that an interval of at least 2 days was required between induction treatment and challenge inoculation. Biocontrol efficacy of P. fluorescens against charcoal rot disease in chickpea was demonstrated under greenhouse conditions.Key words: biological control, induced resistance, Macrophomina phaseolina, Pseudomonas fluorescens.
The influence of edaphic and competitive factors on productivity of marsh reed grass (Calamagrostis canadensis) in a cooperative pathosystem
Authors: Winder Richard S , Macey Donna E
Published: April 2011

Calamagrostis canadensis (Michx.) Beauv., marsh reed grass, hinders the regeneration of conifer seedlings. The influence of nutrients, autoallelopathy, and intraspecific competition on the productivity of greenhouse-grown marsh reed grass inoculated with a combined Fusarium avenaceum (Fr.:Fr.) Sacc.  Pseudomonas sp. pathosystem was studied. The productivity of uninoculated plants increased following fertilization, but these increases were not observed in inoculated plants. Leaf damage in inoculated plants was enhanced by P and K fertilization, but shoot height was not affected. Autoallelopathic straw extract interacted with intraspecific competition to nearly double pathogenic inhibition of shoot growth at high levels of competition. The straw extract also interacted with N fertilizer to reduce shoot productivity. Shoot growth was inhibited at higher levels of intraspecific competition. Responses to nutrients, autoallelopathy, and competition may be useful in developing improved biological control strategies.Key words: Fusarium avenaceum, rhizobacteria, biocontrol, bioherbicide, fertility, soil ecology.
Enzymes of choline synthesis in diverse plants: variation in phosphobase N-methyltransferase activities
Authors: Lorenzin Deborah , Webb Candace , Summers Peter S , Weretilnyk Elizabeth A
Published: April 2011

S-adenosyl-L-methionine dependent phospho-base N-methyltransferases are involved in the sequential methylations of phosphoethanolamine [Formula: see text] phosphomethylethanolamine [Formula: see text] phosphodimethylethanolamine [Formula: see text] phosphocholine. Phosphocholine is a precursor for the ubiquitous phospholipid phosphatidylcholine and for free choline, which can be oxidized to produce the osmoprotectant glycine betaine. Despite the importance of these enzymes to growth and stress tolerance, their activities have been studied in comparatively few plant species. Phospho-base N-methylating activities were assayed in leaf extracts prepared from 17 diverse plant species. All plants tested can perform the first step ( N-methylation of phosphoethanolamine) with in vitro activity rates varying from 0.13 nmol·min1·g1 fresh weight for soybean (Glycine max (L.) Merr.) and pea (Pisum sativum L.) to 25 nmol·min1·g1 fresh weight for cotton (Gossypium hirsutum L.). Of the plant species surveyed, only soybean and pea showed no capacity to perform the two subsequent N-methylation steps. Exposing plants to prolonged dark periods led to decreased phosphoethanolamine N-methylating activity relative to light-exposed controls with the extent of decrease varying among the species from 30% (Limonium perezii (Stapf) F.T. Hubb) to over 90% (Spinacia oleracea L., Beta vulgaris L., and Amaranthus caudatus L.). Thus, light-responsive properties and levels of phosphobase methyltransferase activities vary among plants with a trend towards higher activities being found in plants that accumulate glycine betaine.Key words: glycine betaine, choline, phosphatidylcholine, phosphocholine.
Morphology, taxonomy, and nomenclature of theChrysomyxa ledicomplex and related rust fungi on spruce and Ericaceae in North America and Europe
Authors: Crane Patricia E
Published: April 2011

Rust fungi in the genus Chrysomyxa Unger occur in boreal forests of the northern hemisphere on Pinaceae (mostly Picea A. Dietr.), and most species alternate to angiosperm hosts in the Ericaceae. About 30 species are known worldwide. Although several species are economically important pathogens of spruce and rhododendrons, knowledge about species delineations, relationships among species on different continents, and life cycles is lacking. A group of species with similar spore size, including the Chrysomyxa ledi de Bary complex, was re-examined using field observations, inoculation experiments, and light and scanning electron microscopy. In addition to host specificity, characters found useful in species delineation were urediniospore and aeciospore size and shape, and ornamentation of spores and the aecial peridium. Detailed descriptions are given for eight Chrysomyxa species, including synonyms, types, distribution, relationship to other species, and disease impact. The members of the C. ledi complex are considered separate species: Chrysomyxa ledi on Ledum palustre, Chrysomyxa nagodhii sp.nov. on Ledum groenlandicum and Ledum decumbens, Chrysomyxa neoglandulosi sp.nov. on Ledum glandulosum, Chrysomyxa cassandrae on Chamaedaphne calyculata, Chrysomyxa rhododendri on Rhododendron spp., and Chrysomyxa vaccinii comb.nov. on Vaccinium parvifolium. Chrysomyxa chiogenis, with similar spore size, is included for comparison. A previously unrecognized small-spored species, Chrysomyxa reticulata sp.nov., is described on Ledum spp. and Rhododendron spp. Evidence is presented that C. reticulata spreads from native Ledum spp. in North America to cultivated rhododendrons. A new anamorphic species, Peridermium zilleri, likely belonging in Chrysomyxa, is described on Picea sitchensis from coastal British Columbia.Key words: Uredinales, Rhododendron, needle rust, Ledum, systematics.
Dendroclathra caeruleofusca gen.nov. et sp.nov., an aeroaquatic hyphomycete from Cuba
Authors: Voglmayr Hermann , Delgado-Rodríguez Gregorio
Published: April 2011

Dendroclathra caeruleofusca gen.nov. et sp.nov. is described and illustrated from submerged wood collected in Cuba. The most similar genera are Sympodioclathra, Clathrosphaerina, Pseudoclathrosphaerina, Clathrosporium, Spirosphaera, Pseudaegerita, and Beverwykella, but none of these include the unique combination of features observed in Dendroclathra (treelike branching conidial initial in combination with densely interwoven, irregularly fusing, and dark bluish-grey clathrate conidial filaments). Therefore, a new genus is proposed for this aeroaquatic fungus growing on temporarily submerged wood.Key words: Dendroclathra caeruleofusca, aeroaquatic, hyphomycete, mycoflora of Cuba.
Effect of leaf habit and soil type on nutrient resorption and conservation in woody species of a dry tropical environment
Authors: Lal C B , Annapurna C , Raghubanshi A S , Singh J S
Published: April 2011

We examined 90 dry tropical tree species growing on contrasting soil types (relatively infertile Ultisol and more fertile Inceptisol) for leaf traits such as leaf habit, specific leaf mass (SLM, leaf dry mass per leaf area), leaf chemistry (nutrient concentrations and C/N ratios), and nutrient resorption. Across the species, SLM ranged from 4.06 to 15.74 mg·cm2 in mature leaves and from 2.60 to 15.12 mg·cm2 in senesced leaves. Mature leaf N and P concentrations varied from 0.86% to 4.11% and 0.13% to 0.21%, respectively. Senesced leaf N concentrations varied from 0.49% to 1.90% and P from 0.04% to 0.47%. Resorption efficiencies varied from 26% to 83% (mean = 58.32% ± 1.20%) for N and from 16% to 80% (mean = 49.57% ± 1.48%) for P indicating that the woody species of dry tropical environments resorbed different nutrients in substantial amounts to support new growth. Deciduous species had greater resorbed nutrient pools and resorption efficiencies than evergreen species. Compared with the nutrient-rich environment, species from the nutrient-poor environment had a lower resorbed P pool and lower resorption efficiencies for N and P, but had similar N and P concentrations in mature leaves. Resorption efficiencies for C, N, and P were generally correlated, suggesting that the resorbed C pool acted as a vehicle for mobilizing nutrients, especially N. Species with a low or high C/N ratio in senesced leaf and a low or high N resorption efficiency occurred in both nutrient-poor and nutrient-rich environments, as well as among deciduous and evergreen leaf habits, indicating individualistic adaptations to optimize the efficiency of nutrient resource use and conservation of the dry tropical woody vegetation.Key words: leaf chemistry, leaf traits, resorption efficiency, resorbed nutrient pools, substrate-quality stability.
Shade responses of five grasses native to southwestern U.S. Pinus ponderosa forests
Authors: Naumburg Elke , DeWald Laura E , Kolb Thomas E
Published: April 2011

Recent increases in Pinus ponderosa Dougl. ex Laws. forest density in the southwestern United States have severely reduced understory herbaceous biomass and altered understory species composition. To examine whether changes in graminoid species composition are caused by increased shading, we studied the effects of shade on leaf gas exchange, biomass, and reproductive characteristics of five grass species native to Arizona P. ponderosa forests in a greenhouse study. Blepharoneuron tricholepis (Nash) Torr., Koeleria cristata (L.) Pers., Festuca arizonica Vasey, Muhlenbergia montana (Nutt.) Hitchc., and Sitanion hystrix (Nutt.) J.G. Smith were grown under three light levels representative of photosynthetic photon flux densities and red/far-red ratios that occur beneath P. ponderosa canopies. In general, all species grew better under unshaded conditions, but all survived and flowered even under the dense shade treatment. Reduction of net assimilation rate by shading was the strongest during early reproductive shoot growth for all species except K. cristata, whose assimilation rate was unaffected by shading. Biomass allocation and reproductive responses to shading varied among species. Biomass of S. hystrix was the least affected by shading of all species, and it showed no response in biomass allocation to reproduction but increased height and weight of individual flower stalks under shade. Overall, S. hystrix and K. cristata, species that occur in dense P. ponderosa stands, were least affected by experimental shading, which suggests that shade is a contributing factor to the distribution of grass species in Arizona P. ponderosa forests.Key words: native grass, leaf biomass, reproduction, photosynthesis, red/far-red ratio.
Masting behaviour in beech: linking reproduction and climatic variation
Authors: Piovesan Gianluca , Adams Jonathan M
Published: April 2011

The question of what triggers masting in beech (Fagus) has been a source of uncertainty and curiosity. Analysing seed production series from Europe (Fagus sylvatica L.), eastern North America (Fagus grandifolia Ehrh.), and Japan (Fagus crenata Blume), for various periods (lasting between 6 and 34 years) over the last 150 years, we find a close relationship between masting (mast year) and preceding growing season climate events (mast year1 and mast year2) in eastern North America and Europe, with tentative indications of this pattern in Japan. A drought in the early summer preceding masting (mast year1) is a very strong predictor in Europe and eastern North America, but drought events were not found for the Japan series. The predictive power is increased in all three regions if there has been an unusually moist, cool summer the year before the drought (mast year2). We suggest that, in this initial moist summer (mast year2), carbohydrate buildup within the trees "primes" them for floral induction the following year (year1). In the European and eastern North American series, a drought event in the early part of the following summer (mast year1) acts as a proximal trigger for the release of those reserves into flower initiation and then seed production.Key words: masting, Fagus spp., floral induction, drought, climatic variation, evolutionary ecology.
Stability of nuclear DNA content among divergent and isolated populations of Fraser fir
Authors: Auckland L D , Johnston J S , Price H J , Bridgwater F E
Published: April 2011

Fraser fir (Abies fraseri (Pursh) Poir.) is an endemic species consisting of six major disjunct populations in the Appalachian Mountains, U.S.A. Nuclear DNA content was measured with laser flow cytometry to determine if genome size differences could be detected among the disjunct populations of Fraser fir and its close relatives, balsam fir (Abies balsamea (L.) Mill.) and Canaan fir (A. balsamea var. phanerolepsis Fern.). The mean DNA content for Fraser fir was 17.2 pg/C, which was similar to the two related fir species. There were no significant differences among disjunct Fraser-fir populations. Mean DNA content differences for fir species in the southern Appalachian Mountains were similar even with speciation events (7000 B.P.) and subsequent population isolation. In the absence of polyploidy or large chromosomal rearrangements, genome size changes in conifers occur on a broad evolutionary time scale.Key words: conifers, gymnosperm, C-values, nuclear genome, Abies fraseri.
Facilitation of Leymus mollis by Honckenya peploides on coastal dunes in subarctic Quebec, Canada
Authors: Gagné Jean-Michel , Houle Gilles
Published: April 2011

Plant recruitment in the very first stages of primary succession is limited by seed availability and harsh abiotic conditions. Facilitation, the positive effect of an earlier successional species on a later successional one, is often significant during primary succession and may result from the trapping of seeds and (or) the improvement of seed germination, seedling emergence, establishment, growth, and survival. We examined the effect of mature Honckenya peploides (L.) Ehrh. (Caryophyllaceae) plants on Leymus mollis Trin. (Poaceae) seedling recruitment on a coastal dune in subarctic Quebec, Canada. Facilitative effects of H. peploides on L. mollis may be critical because the latter species is a key element in the dynamics of the coastal dunes at high latitudes in eastern Canada. Honckenya peploides forms small mounds on the upper beach (the embryo dunes) that are typically distinct from the foredune. Leymus mollis progression towards the upper beach occurs through clonal growth, but seedling recruitment is also significant and contributes to the population genetic diversity. We determined L. mollis seedling emergence and growth and estimated various abiotic variables in two habitats on the upper beach: the embryo dunes and the bare, flat areas beside embryo dunes. Sand accumulation and substrate salinity were higher on the embryo dunes than beside them. Leymus mollis seedling emergence was more important on embryo dunes, although seedling growth was lower there. Our results suggest that the embryo dunes formed by H. peploides facilitate L. mollis recruitment possibly by trapping seeds and improving seed germination and seedling emergence.Key words: coastal dunes, facilitation, Honckenya peploides, interspecific interactions, Leymus mollis, sand burial.
Elements present in mineral nutrient reserves in dry Arabidopsis thaliana seeds of wild type and pho1, pho2, and man1 mutants
Authors: Lott John NA , West M Marcia
Published: April 2011

Comparison of wild type and mutants of Arabidopsis thaliana offers an opportunity to study the genetic control of nutrient storage in seeds. We used energy dispersive X-ray analysis to determine the elements present and their relative amounts in globoids of dry wild-type seeds, as well as seeds of a reduced total P uptake mutant (pho1), a phosphate accumulator (pho2), and a metal accumulator (man1). Globoids are spherical inclusions, rich in phytate that function as a store for inositol, P, K, Mg, Ca, Fe, and Zn. Key findings of this study were the following: (i) globoids in protein bodies from nine different tissues and (or) organs in dry Arabidopsis thaliana seeds contained P, K, Mg, and Ca, and sometimes traces of Fe and Zn; (ii) globoids contained higher Ca and lower Mg amounts than occur in globoids in seeds of most other plant species; (iii) globoids in comparable tissue and (or) organ regions of seeds were very similar in elemental composition for wild type and all mutant plants.Key words: Arabidopsis, dry seeds, phytate, mineral nutrient mutants, phosphorus, globoids.
Pollination can protect maize ovaries from infection byUstilago maydis, the corn smut fungus
Authors: Snetselaar Karen M , Carfioli Margaret A , Cordisco Kelly M
Published: April 2011

Ustilago maydis DC (Corda), the maize smut fungus, causes disease on maize (Zea mays L.) and related species. To determine whether pollination of maize ears affects their susceptibility to U. maydis infection, ears were treated in one of four ways: pollination only, inoculation with compatible haploid U. maydis cells only, pollination followed by inoculation 4 days later, or inoculation followed by pollination 4 days later. Combining a standard method of pollination with the silk channel method of inoculation resulted in reproducible, high levels of pollination and infection in controls. Seventy-seven percent of the kernels on ears pollinated only were fertilized, and 75% of the kernels on ears inoculated only were smutted. Ears pollinated 4 days before inoculation developed only 20% smutted kernels on average, with nearly all tumors forming at the tip of the ear where pollination was probably ineffective. Ears that were inoculated 4 days before pollination were 73% smutted, with only 8% average successful fertilization. Microscopic examination of silks after pollination and inoculation treatments indicated that an abscission zone formed at the bases of pollinated silks and may have prevented fungal infection filaments from growing into the ovaries. These results indicated that pollination rendered ovaries more resistant to infection by U. maydis.Key words: Ustilago, corn smut, pollination, resistance.
Factors limiting hybridization betweenPenstemon spectabilisandPenstemon centranthifolius
Authors: Chari Jeannie , Wilson Paul
Published: April 2011

Speciation involves the formation of reproductive isolating mechanisms such as a difference in pollinators, incompatibility between pollen tubes and stylar tissue, hybrid seed abortion, or poor growth of hybrid seedlings. We studied reproductive isolating mechanisms in naturally sympatric populations of Penstemon spectabilis Thurber and Penstemon centranthifolius (Benth.) Benth. where F1hybrids occurred at very low frequency. We compared conspecific crosses, backcrosses, and heterospecific crosses in terms of pollen grain germination, pollen tube growth, fruit set, seed set, and offspring performance. We found several postpollination barriers to hybridization. When P. spectabilis was the ovule parent, the lack of natural hybridization was partially explained by the presence of two isolating factors: reduced pollen tube growth and reduced seed set. When P. centranthifolius was the recipient, the barrier to hybridization was nearly 100% effective and occurred primarily at the stages of pollen grain germination and fruit set. The success of backcrossing was generally intermediate between conspecific and heterospecific crossing. For these two species, it is likely that partial pollinator specificity in addition to strong postpollination reproductive isolating mechanisms contribute to maintaining the species boundary.Key words: speciation, hybridization, introgression, Penstemon, reproductive isolating barriers.
Cellulolytic and pectinolytic activities of Capnodium isolates (sooty mould) from Zimbabwe
Authors: Mwenje E , Mguni N
Published: April 2011

The cellulolytic and pectinolytic activities of five Capnodium (sooty mould) isolates previously associated with preharvest spoilage of avocado (Persea americana Mill.) fruits in Zimbabwe were assessed in liquid culture and in artificially infected avocado fruits. Polygalacturonase, endo-1,4-β-glucanase, and exo-1,4-β-glucanase activities were determined by measuring the increase in reducing groups using the dinitrosalicylic acid method, while for pectin lyase activity the thiobarbituric acid method was used. The five isolates showed the ability to produce polygalacturonase, pectin lyase, and endo-1,4-β-glucanase enzymes. Exo-1,4-β-glucanase activity was only detected in infected avocado tissue. The greyish black Capnodium isolates (Av7, Av8, and Av12) belonging to group I showed higher polygalacturonase and pectin lyase activities in both liquid culture and infected fruits than isolates Av3 and Av10 from group II. The same isolates showed higher exo-1,4-β-glucanase activity in infected avocado fruits. Results indicate that Capnodium, which normally is nonpathogenic, secretes cell wall degrading enzymes, especially pectic and cellulase enzymes. The detection of these enzymes in inoculated avocado fruits suggests a possible role in the preharvest soft rot of avocado fruits caused by Capnodium in Zimbabwe.Key words: Capnodium, sooty mould, pectic enzymes, avocados, cellulases.
Uncommon branching pattern within conifers: Frenelopsis turolensis, a Spanish Early Cretaceous Cheirolepidiaceae
Authors: Daviero Véronique , Gomez Bernard , Philippe Marc
Published: April 2011

The fossil plant Frenelopsis turolensis Gomez from the Lower to Middle Albian of the Escucha Formation (Iberian Ranges, Spain) displays a combination of leaf and branch arrangements unknown in extant conifers. Detailed architectural analyses allow for elucidation of the branching pattern of this species. Branching occurs above a leaf of the whorl but at some distance from the node, within the internodal region. This event may be the result of adnation or hypomerithallus formation. We point out a new type of branching pattern for Frenelopsis based on F. turolensis, with no discontinuity in the leaf sequence. This unusual ontogeny of the branches asserts that branching is more diverse in the fossil cheirolepidiaceous genus Frenelopsis than previously supposed.Key words: branching pattern, ontogeny, Cheirolepidiaceae, Frenelopsis, Cretaceous, Spain.
Litter decomposition in a cool temperate deciduous forest
Authors: Lousier J. D. , Parkinson D.
Published: April 2011

Amounts of autumn tree leaf litter fall, understory litter input, tree leaf litter nutrient input, and rates of dry weight loss in decomposing leaf litter were estimated in an aspen woodland (Populus tremuloides Michx. – P. balsamifera L.) site in the Rocky Mountains in southwestern Alberta. Tree leaf litter input amounted to 250 g m−2 and comprised 3.7% of the total organic matter in the ecosystem (1.92 × 105 kg ha−1). The ratio of the weight of aspen leaf fall to balsam leaf fall was about 6:1. The tree leaf litter input and the total litter input figures were similar to those for other Northern Hemisphere aspen forests. The understory litter input in the study plots was measured as 99 g m−2. The importance by weight of some of the nutrients returned to the soil via tree leaf litter fall was Ca > N > K > Mg > P > Zn > Fe > Mn > Na > Cu. The total weight of these nutrients returned to the soil was 116 kg ha−1, with N, Ca, and K comprising 89% and Mg and P comprising 9.8% of the total.The dry weight loss of decomposing aspen and balsam leaves was measured at 1-, 5-, 8-, 12-, 18-, 24-, and 30-month intervals by using 3-mm-mesh litter bags, and at 12-, 24-, 36-, 48-, and 60-month intervals by using 10-mm-mesh bags. Litter-bag mesh size was of little consequence to the rate of dry weight loss for the first 12 months, but subsequent dry weight loss was greater in the 3-mm-mesh bags, which maintained higher, more representative, moisture conditions than did the 10-mm-mesh bags. However, tethered leaves lost 1.7 times more weight over the first 12 months of decomposition than did confined litter. The decay rate decline with time and with the depth of the litter bag in the litter layers, with maximum dry weight loss occurring over the period encompassing the fall freeze, winter, and the spring thaw and runoff. Leaf litter placed on north-facing slopes was characterized by significantly slower decay rates than that on south-facing slopes.The dry weight loss for aspen leaf litter was 26.2 ± 2.0% after 12 months. 40.0 ± 1.6% after 30 months, and 58.7% after 60 months (by regression): for balsam litter it was 21.2 ± 1.9% after 12 months, 37.4 ± 1.7% after 30 months, and 47.9% after 60 months (by regression). The highly leachable component of leaf litter was estimated at 23.1% for aspen and 21.4% for balsam. The time required for 99% decomposition was calculated as about 24 years for aspen and about 27 years for balsam, which gives average annual decay rates of 3.2% for aspen and 2.9% for balsam. The decay rate for Populus leaf litter was lower than that for aspen in Alaska and appeared to fit the range for deciduous leaf litter from some forested IBP Tundra Biome sites.
Growth and metabolism of cells and tissue of jack pine (Pinus banksiana). 4. Changes in amino acids in callus and in seedlings of similar genetic origin
Authors: Durzan D. J. , Chalupa V.
Published: April 2011

Growth rates of callus from hypocotyls and radicles of jack pine (Pinus banksiana Lamb.) seedlings were associated with the differential release and adherence of daughter cells. From 18 to 40% of the N in the medium was assimilated through the increasing surface area of callus and contributed nearly 6% of the total gain in dry weight. Sequential changes in free amino acid N leading to final size were similar for callus from both plant parts. Changes in N correlated significantly with growth rates and callus density (dry weight per cubic centimetre). When free amino acid N was expressed as a percentage of the total soluble N, correlations signified the relative proportions of the amino acid pool that gave different growth-rate forms. The balance of N metabolism during the autocatalytic growth of hypocotyl callus was under the influence of free glutamine, whereas the exponential growth of radicle callus was dominated by the synthesis of asparagine N. In callus from both plant parts 80 to 87% of the net gain in N was recovered in the bound (protein and nucleic acid) fraction. Percentage of free glutamine N decreased with the increase in bound N.Ways in which free amino acid N interacted with growth rates indicated that final size may be usefully defined not merely as an extreme of a growth function but in more sequential kinetic terms supported by a series of correlation coefficients. Correlations revealed the specific points at which free amino acids interacted strongly with rates.When amino acid N in callus was compared with N in seedlings from which callus was derived, the trends were strikingly similar. In seedlings the succession of amino acids was linked more to the uptake of N from the gametophyte by cotyledons and daughter cells in growing tissues rather than to their morphogenesis. Differences related mainly to the greater ability of the seedling to synthesize protein and to maintain higher levels of total soluble N than in callus.
Growth and metabolism of cells and tissue of jack pine (Pinus banksiana). 6. Free nitrogenous compounds in cell suspension cultures of jack pine as affected by light and darkness
Authors: Durzan D. J. , Chalupa V.
Published: April 2011

The increases of dry weights for cell suspensions of jack pine (Pinus banksiana Lamb.) callus grown in light or darkness were near-exponential, but the final weight was 10% less for those grown in darkness. Per unit weight, free amino acid N accumulated in cells in light but was lost from cells in darkness. Composition was dominated by high levels of glutamine, arginine, and alanine N. Several compounds, not usually present in callus on agar, or in the donor seedlings, were detected in cells.The composition of cells in relation to the external medium altered markedly. Individual nitrogenous compounds correlated with overall growth rates. Correlations between rates and composition reflected the distribution of clump sizes, i.e. differential daughter cell adhesion. Moreover, depending on the type of N compound studied, the ratio of endogenous to exogenous N either remained constant or varied, to reflect the growth habit of the suspension. Ratios for free glutamine N and monosubstituted guanidines were responsive to light and darkness and complemented one another.
The fatty acid composition of some Sphagnum species
Authors: Koskimies Kristiina , Simola Liisa Kaarina
Published: April 2011

The fatty acid composition of total lipids was studied in gametophytes of Sphagnum fimbriatum, S. majus, S. magellanicum and S. nemoreum cultivated aseptically at a constant temperature of 25 °C. It was found to be very similar in these four bog mosses, and also fairly similar to that of other bryophytes. The lipid content of these species was about 6% of the weight of the freeze-dried plant material. The fatty acid composition of different lipid fractions (neutral, glyco-, and phospholipids) was studied in S. fimbriatum and S. majus. Eicosapentaenoic acid (20:5) is abundant (~ 40%) in the triglycerides, and arachidonic acid (20:4) (30%) in the steryl and methyl ester fraction. Linolenic acid (18:3) formed about 60% of the fatty acids in the mono- and digalactosyl diglycerides. This fatty acid occurs only in low concentrations (~ 10%) in the triglycerides. Palmitic (16:0) and linoleic (18:2) acids are the most important fatty acids of the phospholipids.
Histological and ultrastructural observations of Medicago sativa root nodule senescence after foliage removal
Authors: Vance C. P. , Johnson L. E. B. , Halvorsen A. M. , Heichel G. H. , Barnes D. K.
Published: April 2011

Root nodules from control and defoliated alfalfa (Medicago sativa L.) were compared for a period of 18 days following defoliation. Bacteroid containing cells of the nodules decreased markedly for the first 10 days following defoliation, but then increased during the next 8 days. Nodule length increased continuously during the 18 days in both control and defoliated plants. Cellular integrity of vascular bundles, meristems, and infection threads was retained in nodules from treated and control plants throughout the experiment. The sequence of senescence in bacteroid containing cells was similar in nodules from both treatments. Senescence was initially observed in the cytoplasm of bacteroid containing cells. Membranes surrounding bacteroids showed degenerative changes as bacteroids senesced. Bacteroids aggregated within nodule cells. Infection threads and bacteria inside infection threads did not disintegrate. Bacteroids ultimately disappeared in senescent cells.Nodules of alfalfa appear to respond to foliar harvesting by a partial but temporary senescence from which they recover by regeneration of bacteroid containing cells.
Callus and adventitious shoot formation in excised embryos of white pine (Pinus strobus)
Authors: Minocha Subhash C.
Published: April 2011

Excised embryos from 2- to 3-year-old seeds of white pine (Pinus strobus) were grown on Murashige and Skoog medium supplemented with several concentrations of different plant hormones. In the basal medium the embryos developed into normal seedlings. At 1–2% sucrose concentration in the medium, the primary root of the embryo did not grow well, while at 3–6% sucrose concentration normal growth of the primary root was observed in most of the embryos.Gibberellic acid at a wide range of concentrations (0.01–20.0 mg/L) had little effect on the growth of the seedling shoot while growth of the primary root was generally suppressed. In the presence of 0.01–2 mg/L of NAA, 2,4-D, or IBA, the embryos proliferated to form friable green callus. Callus formation was further enhanced by a cytokinin (0.1-5 mg/L). IBA (1–5 mg/L) in some embryos induced the formation of adventitious shoots from the hypocotyl region. Similarly, TIBA (0.5–1.0 mg/L) induced the formation of adventitious shoots but they were formed at the tips of embryonic cotyledons. The number of adventitious shoots per embryo was increased by zeatin or benzyladenine.The callus obtained on 2,4-D or IBA could be easily subcultured. In spite of several treatments with different auxins, cytokinins, and their combination, no differentiation of roots or shoots was observed in callus cultures.
14C incorporation into sugars and changes in starch during feminization of castor (Ricinus communis), as influenced by kinetin and morphactin
Authors: Kumar N. Raja , Rao P. Gopala
Published: April 2011

Foliar sprays of kinetin (6-furfurylaminopurine) and morphactin EMD 7301 W (methyl ester of chlorfluerenol) were applied at a concentration of 20 ppm to 6- and 8-week-old plants of castor (Ricinus communis L.). Kinetin suppressed male tendency while morphactin did not affect it. Kinetin elicited an increase in femaleness and a decrease in maleness, consequently causing reduction in the total number of flowers, compared with the number of flowers in the control plants. Morphactin simulated kinetin in not only increasing the female tendency but also in increasing the 14C incorporation into sugars. Increased femaleness did not appear to involve starch hydrolysis however, it was correlated with a higher level of sucrose in the leaves.
The decline of Myriophyllum spicatum in a eutrophic Wisconsin lake
Authors: Carpenter Stephen R.
Published: April 2011

The recent changes in the submersed macrophyte communities of Lake Wingra, Wisconsin, have been dominated by the dynamics of one exotic species. After a decade of abundance, Myriophyllum spicatum has undergone a sustained decline in the Madison lakes. A pattern of explosive growth followed by declining abundance may describe most M. spicatum invasions.No simple single-factor explanation can adequately account for the biomass dynamics of M. spicatum in Lake Wingra. The decline in M. spicatum biomass appears to be the result of a complex of synergistically interacting factors, perhaps including nutrients, epiphytes, competitors, and parasites or pathogens.Invasions of lake districts by M. spicatum are hypothesized to follow a wave pattern. When interlake distances are accounted for, departure from a simple wave is hypothesized to result from lags in infestation of lakes which are not susceptible to colonization by M. spicatum. Several testable hypotheses are suggested by this view of M. spicatum invasions.
A note on Agyrium sedecimsporum from Idaho
Authors: Paden J. W.
Published: April 2011

Agyrium sedecimsporum is recorded for the first time from North America. A description and illustrations are furnished.
Relationship of the production of the toxin, cerato-ulmin, to synnemata formation, pathogenicity, mycelial habit, and growth of Ceratocystis ulmi isolates
Authors: Takai Shozo
Published: April 2011

Forty-seven isolates of Ceratocystis ulmi collected from Canada, the United States, the United Kingdom, France, the Netherlands, and Iran were classified with respect to their ability to produce cerato-ulmin (CU) and synnemata, their radial growth, mycelial habit, and pathogenicity.Twenty-nine isolates clearly produced CU in a measurable quantity while 18 isolates produced it only in trace quantities. In general, the former produced fluffy mycelium and were active in synnemata formation. They were aggressive in pathogenicity with one exception. The latter group of isolates generally produced waxy, yeastlike mycelium and formed very few synnemata. They were all nonaggressive in pathogenicity. Radial growth was generally higher among the isolates that produced CU in larger quantities than among those producing CU in trace quantities. The relationship between CU production and pathogenicity affords a method for estimating isolate pathogenicity without the need for host inoculation.
Actin in motile and other processes in plant cells
Authors: Williamson R. E.
Published: April 2011

The occurrence of actin in plant cells is described. Evidence is summarized in favour of the view that its role in animal cells may extend beyond force production for conspicuous motile events. Actin's role in cytoplasmic streaming in plants is then discussed and the possibility of its involvement in other aspects of plant cell physiology is raised.
Are there contractile proteins present in phloem?
Authors: Thompson R. G.
Published: April 2011

Actinlike structures have been found in companion cells and parenchyma of phloem and in young sieve cells, but not, according to recent work, in mature sieve tubes of angiosperms. Because of this, the question of whether P-protein is a contractile protein presents serious difficulties. Protein of low molecular weight found in phloem has not been as carefully examined as P-protein. Evidence to support contractile proteins in phloem as seen from the amino acid composition and respiratory activity of willow bark is also discussed.
Freeze preservation of pea meristems: cell survival
Authors: Haskins R. H. , Kartha K. K.
Published: April 2011

Microscopic examination of semithin and ultrathin median longitudinal sections of shoot apical meristems revealed little adverse effect from the dimethyl sulfoxide treatments and the differentiation medium used. Freeze preservation was followed by storage in liquid nitrogen for 1 h. In the meristems which remained viable most of the actively growing cells were located on primordial leaf tissues and in the axillary bud and stipule meristematic areas. Growth generally resumed at many sites, and some of these were close to or in the "dome" area.
Interactions entre mitochondries et chloroplastes dans la cellule. III. Evolution des échanges gazeux des spores de Funaria hygrometrica au cours d'un séjour à l'obscurité
Authors: Chevallier D. , Nurit F. , Douce R.
Published: April 2011

In darkness, in an inorganic liquid medium the spores of Funaria hygrometrica demonstrate a rapid increase from low to high metabolism activity with mitochondrial respiration functioning at its maximal value. The spore respiration is high during a short period of time corresponding to the transformation of the proplastids into chloroplasts. Then, the spore respiration slows down progressively. This diminution is due to a rapid decrease of the general metabolism. Under these conditions, the germination cannot take place and the spores appear to return to a quiescent state.
Microbial populations associated with buds and young leaves of apple
Authors: Andrews John H. , Kenerley Charles M.
Published: April 2011

Apple buds and developing leaves and floral parts were assessed for microbial populations by a washing procedure and scanning electron microscopy (SEM) at six stages ranging from dormancy through early tight cluster. Densities of yeasts, filamentous fungi, and bacteria associated with dormant buds were on an order of magnitude of 5 × 105 propagules per gram fresh weight of tissue. Populations tended to peak as buds swelled and to diminish during subsequent developmental stages. External surfaces of buds were colonized extensively. Internal surfaces, particularly those of the peripheral scales, also supported abundant microflora. Evidence from SEM suggested that few microorganisms were associated with floral and leaf primordia. Surface sterilization was not found to be an adequate method to discriminate between external and internal bud microflora. A partial list of microorganisms included fluorescent pseudomonads, Aureobasidium pullulans, and species of Cryptococcus, Sporobolomyces, Rhodotorula, Coniothyrium, Alternaria, Phomopsis, Phoma, Epicoccum, Cladosporium, Acremonium, Fusarium, Stachybotrys, and Sclerotium. These data are pertinent to the microbial ecology of the gemmisphere and to the prospective biological control of foliar pathogens.