bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions of the bean rust and cowpea rust fungi with species of the Phaseolus – Vigna plant complex. I. Fungal growth and development
Authors: Elmhirst Janice F. , Heath Michèle C.
Published: September 2008

Growth and development of two closely related rust fungi, Uromyces appendiculatus and U. vignae (uredospore infections), were compared in several American and African species of the Phaseolus – Vigna plant complex and in Lablab purpureus. In plants inoculated with U. appendiculatus the frequency of formation of both primary and secondary haustoria generally decreased with evolutionary distance from the American host species. Uromyces appendiculatus formed primary haustoria at a high frequency of infection sites in most American and many African species, and also sustained a limited haustorium – plant cell metabolic relationship (as determined by the amount of secondary fungal growth) in one group of African species. Uromyces vignae generally formed very few haustoria in both American and African species not known as hosts of the fungus; however, growth of U. vignae colonies occasionally continued for some time at a few infection sites in nonhost species without sporulation. The implications of these results are discussed with respect to the coevolution of the two fungi with their hosts.
Starch-granule distribution between cell types of alfalfa nodules as affected by symbiotic development
Authors: Hostak M. S. , Henson C. A. , Duke S. H. , VandenBosch K. A.
Published: September 2008

The distribution of starch granules between infected and uninfected cells in the central and cortical regions of alfalfa (Medicago sativa L.) nodules was investigated by morphometry of light micrographs of semithin sections of resin-embedded specimens. Nodules were collected from greenhouse-grown plants at early anthesis. The influences of symbiotic development on starch granule distribution were also investigated. In the early infection zone, infected cells had 1.7 times more starch granules and 1.5 times more starch per cell than uninfected cells. In the middle and late infection zones no significant differences in granule numbers or starch per cell occurred between cell types. Uninfected cells had greater starch density and smaller cell size than infected cells. Starch quantity and density in both cell types decreased from early infection to onset of senescence, with infected cells losing starch more rapidly. Comparisons between nodules from plants placed in darkness for 48 h and nodules from plants grown in light–dark cycles showed that starch depletion (starch area per cell and starch density) occurs more rapidly in infected cells than in uninfected cells. We conclude (i) that starch metabolism does not occur exclusively or even primarily in one cell type and (ii) that during prolonged periods of reduced photosynthesis infected cells deplete starch reserves faster than uninfected cells.
The effect of lignin and nitrogen on the decomposition of litter in nutrient-poor ecosystems: a theoretical approach
Authors: Berendse Frank , Berg Björn , Bosatta Ernesto
Published: September 2008

A model is developed to study the dynamics of carbon and nitrogen in decomposing substrates that contain different organic compounds: (i) lignin, (ii) carbohydrates "masked" by lignin compounds, and (iii) free carbohydrates. Under conditions both of carbon limitation and of nitrogen limitation the model predicts a negative linear relationship between lignin concentration and rate of mass loss. The coefficients of this relationship are determined by microbial properties and by the ratio (ac) between the amount of "masked" carbohydrates and the amount of lignin in the litter. Litter decomposition data of three different ecosystems are used to obtain estimates of the ratio ac. The calculated values are in the same range as values estimated on the basis of the course of the cellulose/lignin ratio during the decomposition process. When nitrogen limits microbial growth, the model predicts a positive linear relationship between rate of mass loss and initial lignin concentration.
Localization of three sugar residues in the interface of ectomycorrhizae synthesized between Alnus crispa and Alpova diplophloeus as demonstrated by lectin binding
Authors: Massicotte H. B. , Ackerley C. A. , Peterson R. L.
Published: September 2008

The interface established between Alnus crispa and the basidiomycete Alpova diplophloeus involves structural modifications of host cell walls and hyphal walls in the Hartig net region of the ectomycorrhizae synthesized in pouches. Indirect labelling of cell wall carbohydrates by using colloidal gold conjugated with the lectins Ulex europaeus agglutinin, wheat-germ agglutinin, and concanavalin A was applied to these mycorrhizae and to nonmycorrhizal roots. Significantly more binding of the lectins was observed in the mycorrhizal roots than in control roots. In the Hartig net region of mycorrhizal roots, the lectins bound intensely to the host cell wall, particularly the wall ingrowths, and to adjacent fungal walls, whereas in nonmycorrhizal roots, a sparse labelling was recorded in the cell wall. Possible explanations for this pattern of lectin binding include the following: the sugar residues L-fucose, mannose, and N-acetylglucosamine may be utilized in the synthesis of the elaborate epidermal wall ingrowths and N-acetylglucosamine may be utilized in the synthesis of the labyrinthine wall branchings of the fungus; the sugar residues are bound to a proteinaceous fraction in the host and hyphal walls; the sugar residues bound by the lectins may be components of defense reaction elicitors released from the host wall and hyphal wall by wall-degrading enzymes; the sugar residues may simply be the result of enzymatic degradation of walls but not involving elicitors of defense reactions.
Bog profile evidence of fire and vegetation dynamics since 3000 years BP in the Acadian Forest
Authors: Wein Ross W. , Burzynski M. P. , Sreenivasa B. A. , Tolonen K.
Published: September 2008

An attempt has been made to characterize fire prehistory and its effect on Acadian Forest vegetation by microscopic examination of charred particles and pollen preserved over the last 3000 years in bogs near Marcelville and Fredericton, New Brunswick, Canada. A background accumulation rate of about 0.15 mm2∙g dry weight−1 ∙year−1 of charred particles was found in each sample, indicating a constant rain of distant-source, small particles. Proximity of the source fire to the site of particle deposition was estimated with the aid of two charred particle transport studies conducted during prescribed burns. Charred particles of 44 400 μm2 and larger were found up to 1 km from the source, with a wind speed of 20 km/h. Smaller particles remained in the air column for much longer and are of less use for determining local fires. Analysis determined periods of province-wide fires and subsequent forest composition changes. The greatest of these occurred at about 2200, 1750, 1550, and 400 years BP. Temporal patterns of charred particle peaks were similar in the two bogs and support data from Nova Scotia and Maine. Fires seem to have accompanied the establishment of the present-day forest type in the period around 1450 years BP.
Carex lyngbyei excluded from the flora of eastern North America, and taxonomic notes on related species and hybrids
Authors: Cayouette Jacques
Published: September 2008

Carex lyngbyei has been reported from a few stations in eastern North America over the last century. Herbarium specimens so identified from that area are morphologically very diverse and are quite different from the typical C. lyngbyei along the North Pacific coastline and Iceland. This eastern material was found to belong to four species (C. aquatilis, C. crinita var. gynandra, C. paleacea, and C. recta) and six different hybrids (C. ×saxenii, C. ×gardneri, C. ×exsalina, C. ×subnigra, C. ×super-goodenoughii, and C. ×grantii). Pollen stainability of typical C. lyngbyei and of putative C. lyngbyei from eastern North America supported these revisions: it was high in species and low in hybrids or in species of hybrid origin such as C. recta. In western North America, C. lyngbyei has either 2n = 68, 70, or 72 chromosomes and meiosis appears to be regular. In contrast, some putative C. lyngbyei from eastern Quebec showed a highly disturbed meiosis. Consequently C. lyngbyei is excluded from eastern North America.
Variation in node sequence in var. hypogaea collection of cultivated peanuts
Authors: Bhagat N. R. , Lalwani H. B. , Reddy P. S.
Published: September 2008

The order of occurrence of vegetative and reproductive nodes on the basal primary branch (n + 1) of 100 germ-plasm accessions of Arachis hypogaea L. ssp. hypogaea var. hypogaea belonging to the Virginia runner group was studied. The node sequence started with vegetative nodes in all the 210 plants of 16 accessions, but in the remaining 84 there was variation within and between accessions. Since there was no uniformity, the total plant population of all 100 accessions was pooled. In general, the first node was predominantly vegetative in the population (about 81.5% plants). In the two-order sequence, the pattern starting with vegetative nodes followed by reproductives was classified into six classes and in the reproductive followed by vegetative category, there were five classes; the node numbers in both ranged from three to five. The order 1 vegetative + 2 reproductive was more predominant (50 % plants). In the three-order sequence, there were 13 classes in the vegetative + reproductive + vegetative sequence and 10 classes in the reproductive + vegetative + reproductive sequence with node numbers ranging from four to seven in both. In the former, 1 vegetative + 2 reproductive + 2 vegetative and 1 vegetative + 2 reproductive + 1 vegetative sequences were more frequent (29.2 and 20.2% plants, respectively). It was concluded that wide variation in vegetative and reproductive node numbers and their sequence in the varietal collection of Virginia runner peanuts might have developed in nature as a result of genetic introgression and, thus, may not be considered a dependable attribute in the classification of cultivated peanuts.
Bisporella resinicola comb.nov. and its Eustilbum anamorph
Authors: Seifert Keith A. , Carpenter Steven E.
Published: September 2008

Helotium resinicola is transferred to the genus Bisporella as Bisporella resinicola comb.nov., and the history of its anamorph is traced, resulting in the resurrecting of the anamorph genus Eustilbum and the new combination Eustilbum aureum. The holomorph is described and illustrated, and its ecology is briefly discussed.
Improved bunt inoculation of wheat utilizing adventitious shoots
Authors: Kawchuk L. M. , Nielsen J.
Published: September 2008

A procedure is described of injecting inoculum of dwarf or common bunt at the bases of the internodes of wheat. Physical stimulation by wounding of the intercalary meristem located above the nodes resulted in the formation of adventitious shoots. If inoculum of dwarf or common bunt is injected at the time of stimulation, the spike of the resulting shoot is usually infected. This procedure shortened the period between teliospore germination and production of sori, gave a high infection rate, and induced several infected spikes on one primary stem.
Winterella, the correct name for Cryptospora and Ophiovalsa
Authors: Reid James , Booth Colin
Published: September 2008

Winterella O. Kuntze is proposed as the correct generic name for the fungi previously assigned to Cryptospora Tul. & C. Tul. and Ophiovalsa Petr. Eleven species are accepted in the genus, including Winterella confusa sp.nov., W. wehmeyeriana sp.nov., W. albofusca (Cooke & Ell.) comb.nov., W. alnicola (Höhn.) comb.nov., W. aurantiaca (Wehm.) comb.nov., W. aurantiaca subsp. valsoides (Rehm) comb.nov. Two new genera are proposed, Mycocryptospora (type M. anthostomoides (Rehm) comb.nov.) and Servazziella (type S. longispora (Servazzi) comb.nov.). Forty-nine other fungi with names in the genus Cryptospora are discussed and, when possible, a disposition is suggested.
Changements cytochimiques et ultrastructuraux des parois cellulaires de la pellicule du raisin, Vitis vinifera, durant la croissance et la maturation de la baie
Authors: Rajaei Homa
Published: September 2008

Cytochemical and ultrastructural analysis of cell wall characteristics was performed in the dermal system of the grape berry (Vitis vinifera L. cv. Pinot noir), using a test for polysaccharides (periodic acid – thiosemicarbazide – silver proteinate, associated with dimethylsulfoxide extraction). Samples were examined at successive stages of fruit development. The main events of the first growth phase, i.e., thickening of hypodermal cell walls and their tangential extension, continued during the second growth phase. At all the stages of grape development, tangentially expanding walls were typical of actively growing plant cell walls, with an ordered texture, new layer deposition, and progressive rotation of microfibrillar subunits (bow-shaped patterns). At maturity, hydration, swelling of the walls, and an increase in the amount of soluble pectic substances were noticed. No redifferentiation of the cell walls occurred. The cuticle, already differentiated into two layers at the first growth phase, was clearly lamellar during the second. At maturity a number of layers, distinguishable by their cytochemical reactivity, were detected. Cuticle thickness increased during "véraison" and was maintained throughout the second growth phase. A considerable increase in the content of epicuticular waxes was noticed during ripening.
Isolation and characterization of Frankia strains isolated from Myrica gale
Authors: St-Laurent Louis , Lalonde Maurice
Published: September 2008

From 20 provenances of field-collected actinorhizae of Myrica gale, more than 3000 test tubes were inoculated with OsO4-treated nodules. Only 30 Frankia strains were isolated from 6 provenances. Most isolates showed an extremely slow growth in the various isolation media tested. For 12 strains whose growth was sufficient, the Frankia nature of isolates was verified by morphological characterization and biochemical analysis, using gas chromatography for the presence of 2-O-methyl-D-mannose. All 12 strains showed infectivity on M. gale and Alnus glutinosa. Five of those strains were ineffective on A. glutinosa but effective on Elaeagnus angustifolia and Hippophaë rhamnoides.
Nonspecific action of polygenes in Ustilago hordei
Authors: Christ B. J. , Person C. O.
Published: September 2008

Previous genetic analysis of Ustilago hordei (Pers.) Lagerh. indicated that virulence was modified by polygenes. The analysis was extended in this study to include examination of this variation on both the susceptible barley cultivar Odessa and the resistant cultivar Trebi. Generally, higher percentages of smutted plants were observed on 'Odessa' than on Trebi'. The rankings of dikaryons were similar on both cultivars and correlations of rankings of dikaryons between cultivars were statistically significant (rs = 0.875 and rs = 0.78). Interactions between haploid genotypes also were observed which greatly enhanced the percentage of smutted plants. Rather than virulence being dominant as reported in the previous analysis, all segregation patterns from these experiments indicated that virulence was recessive.
Morphological and isozyme variation in Salicornia europaea (s.l.) (Chenopodiaceae) in northeastern North America
Authors: Wolff S. L. , Jefferies R. L.
Published: September 2008

Morphological and electrophoretic variation has been documented within and among populations of Salicornia europaea L. (s.l.) in northeastern North America. Univariate and multivariate analyses (discriminant analyses) of measurements of floral and vegetative characters delimited three morphologically distinct groups of populations: Atlantic coast tetraploids (2n = 36), Hudson Bay diploids, and Atlantic coast and James Bay diploids (2n = 18). The two diploid groups were morphologically distinct from the midwestern diploid, S. rubra Nels., based on anther length, width of the scarious border of the fertile segment, and the overall width of the fertile segment. Electrophoretic evidence supported the delimitation of the three distinct morphological groups of populations of S. europaea with the exception of the population from James Bay, which had electrophoretic patterns identical with those of plants from Hudson Bay but resembled the Atlantic coast diploids morphologically. Most enzyme systems assayed were monomorphic. Only homozygous banding patterns were detected in diploid plants and electrophoretic variation was not observed within populations of S. europaea or S. rubra but was detected between groups of populations. Four multilocus phenotypes were evident; these corresponded to the major groups recognized on the basis of ploidy level and morphology. Reasons that may account for the paucity of isozymic variation are discussed.
Taxonomic status of diploid Salicornia europaea (s.l.) (Chenopodiaceae) in northeastern North America
Authors: Wolff S. L. , Jefferies R. L.
Published: September 2008

The taxonomic status of diploid Salicornia europaea L. (s.l.) in northeastern North America has been evaluated based on morphological and electrophoretic variation within and between populations. Populations of two European diploid micro-species, S. ramosissima J. Woods and S. europaea (s.s.), and populations of the midwestern diploid, S. rubra A. Nels., were also examined, affording a comparison between North American S. europaea (s.l.) and recognized species. Anther length, width of the scarious border of the fertile segment, and floral perianth shape were used to subdivide North American diploid populations into two groups. These groups were morphologically distinct from S. rubra and the European microspecies. The electrophoretic profile was unique in each morphologically distinct group of populations of S. europaea (s.l.) in northeastern North America. Based on morphological, geographical, and electrophoretic differences, diploid populations of S. europaea (s.l.) from this region are assigned to one of the following two new species: S. maritima Wolff & Jefferies, sp.nov., and S. borealis Wolff & Jefferies, sp.nov. The tetraploids are retained in S. europaea (s.l.).
Studies on the growth and development of Agropyron repens: interacting effects of humidity, calcium, and nitrogen on growth of the rhizome apex and lateral buds
Authors: McIntyre Gordon I.
Published: September 2008

A previous investigation of apical dominance in the rhizome of Agropyron repens showed that keeping the rhizome in a high humidity promoted the outgrowth of the lateral buds but strongly inhibited the growth of the rhizome apex. A study of these related responses demonstrated that the inhibition of apical growth was not prevented by excision of the lateral buds and was also induced when only the apex of the rhizome received the high humidity treatment. The necrotic lesions that developed in the arrested apices and the reduction of apical inhibition produced by various Ca treatments indicated that the inhibition of apical growth was caused by Ca deficiency. When the rhizome apex was exposed to low humidity, a localized high-humidity treatment of the lateral buds did not release the buds from apical dominance in low-N rhizomes but strongly promoted bud growth at a higher N level. When growth of the buds was induced at low humidity by increasing the N supply, the increase in bud weight was preceded by an increase in the water content of the bud when expressed on a dry weight basis. These results agree with those of previous investigations and suggest that the interacting effects of N and humidity on the water status of the buds may play a significant role in the mechanism of apical dominance.
The pollination mechanism of Engelmann spruce (Picea engelmannii)
Authors: Owens John N. , Simpson Sheila J. , Caron Guy E.
Published: September 2008

The pollination mechanism of Picea engelmannii (Parry) was studied on small potted scions under natural conditions and in controlled environment chambers. Six stages of conelet development were recognized and related to pollen receptivity. Cone-lets appeared receptive for about 2 weeks but were actually receptive for only about 1 week. Secretory droplets appearing on the micropylar arms collected pollen for several days before pollination drops formed. Pollination drops formed acropetally in the conelet and only once from each ovule. Pollination caused rapid recession of the pollination drop, whereas the drop remained for several days on unpollinated ovules. There was some decrease in size of pollination drops during midday and reemergence the following night. Pollination drops were secreted by the nucellar tip in a manner similar to nectaries. Secretory cells collapsed following secretion. The drop contained 4.3% glucose and 3.8% fructose but no sucrose. High humidity increased the longevity and decreased the diurnal fluctuation in size of pollination drops. Conelets from trees with low leaf water potential developed more slowly and produced smaller and more viscous pollination drops. Cones averaged 103 ovuliferous scales, 90% of which were fertile. However, usually less than 50% of the potential seed set was achieved. One of the major causes for low seed set is inadequate pollination. A better understanding of the pollination mechanism and the receptive period may improve seed efficiency in controlled and supplemental mass pollinations.
Oospore germination in Phytophthora megasperma f.sp. glycinea
Authors: Schechter S. E. , Gray L. E.
Published: September 2008

More than 80% of oospores of selected Phytophthora megasperma f.sp. glycinea isolates, grown on lima bean agar, germinated when tested on water agar. Percentage of germinated oospores varied widely among isolates. Oospore production was greatest at temperatures between 18 and 23 °C. Oospores germinated most rapidly at 27 °C. Exposure to light during oospore development had a negative effect on germination, while light during germination had a positive effect.
Formation et évolution des ascospores de Tuber melanosporum (truffe noire du Périgord, Discomycètes)
Authors: Parguey-Leduc A. , Janex-Favre M. C. , Montant C.
Published: September 2008

In Tuber melanosporum, as in a few other truffles (genus Tuber), ultrastructural observations show that each ascospore is delimited in the ascus apical zone through an individual process, the single primordial wall originating from a lomasomic extension. The primordial wall splits into two layers (primary wall), then a secondary part is deposited. At the most complex stage it comprises, from interior to exterior: a regular clear epispore; a dark exospore producing ornamental spines; a clear perispore which strongly dilates then shrinks around each spine; a limiting ectospore. In the mature ascospore, the ascospore wall is composed of only two superimposed parts corresponding to the two ascospore walls visible with light microscope. The clear internal part is the epispore and the brown echinulate external one represents the joined exospore, perispore, and ectospore. The ascospores contain six to eight early formed nuclei and cytoplasmic inclusions. Mitochondria prevail in young ascospores whereas oil droplets nearly fill the mature ones.
Heterostyly, homostyly, and long-distance dispersal of Menyanthes trifoliata to Greenland
Authors: Olesen Jens Mogens
Published: September 2008

An old report of homostyly in Menyanthes trifoliata L. in Greenland has been used as supporting evidence for the generally accepted hypothesis called Baker's law of long-distance dispersal. Measurements of flowers from both Denmark and Greenland throw considerable doubt on the existence of homostyly in this species. Several reports and observations suggest that seeds of M. trifoliata are frequently brought to Greenland by a few species of birds, especially geese, and that its seeds have great buoyancy in water.
Forest types of the North Cascades National Park Service Complex
Authors: Agee James K. , Kertis Jane
Published: September 2008

A forest cover type classification was developed for the North Cascades National Park Service Complex in north central Washington, U.S.A., based on 425 reconnaissance-level plots. Detrended correspondence analysis (DECORANA) was used to ordinate the data. Temperature and available moisture were identified as primary environmental gradients. Two-way indicator species analysis (TWINSPAN) was used to classify the data, resulting in eight forest cover types: ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), subalpine fir (Abies lasiocarpa), whitebark pine – subalpine larch (Pinus albicaulis – Larix lyallii), mountain hemlock (Tsuga mertensiana), Pacific silver fir (Abies amabilis), western hemlock (Tsuga heterophylla), and hardwood forest. The coniferous forest cover types, with the exception of ponderosa pine, were defined to have open and closed canopy components; each cover type includes a variety of plant associations. The cover types were integrated into a geographic information system used to create a cover type map that was 85% accurate. The forest cover types of the park complex are unique not so much for within-community diversity as for the close juxtaposition of cover types with interior and coastal climatic influences.
Quantitative studies in ovule development. III. An estimate of shape changes in Phyllostachys aurea
Authors: Maze Jack , Scagel Rob , Bohm L. R.
Published: September 2008

Multivariate analysis of ovule development data from Phyllostachys aurea determined that there are (i) changes in estimators of organization (eigenvectors of principal components axes, determinants of correlation, and variance–covariance matrices); (ii) differences of a shape component in each axis (angles between principal components axes and a vector of isometry); and (iii) an increase in variation in the parameters calculated. Angles between principal components axes are all significantly different from 0° (zero), when calculated from jackknifed estimates, indicating that each axis represents different shape components. Because these vectors are derived from principal components axes, they are another manifestation of correlation structure, i.e., organization. Thus angular differences between vectors are a function of differences in organization. The relationship between organization and vectors implies that the concept of shape is another way of expressing the organization that is inherent in biological systems. The changing organization, including shape, and increasing variation with development are expressions of the increasing complexity concomitant with development. This increasing complexity would be predicted from the theory of Brooks and Wiley as a manifestation of the second law of thermodynamics as expressed in non-equilibrium systems.
Genetically determined nonselective abortion of asci in Neurospora crassa
Authors: Raju Namboori B. , Perkins David D. , Newmeyer Dorothy
Published: September 2008

In many crosses of laboratory strains of Neurospora crassa, a large proportion of complete asci abort shortly after ascospore delimitation. The aborted asci contain eight small, degenerate, vacuolated ascospores. We use the term "bubble asci" to signify this special form of ascus abortion. The frequency of bubble asci was scored in 8- to 10-day-old perithecia from crosses between closely related strains and between unrelated strains. When two unrelated or distantly related strains are mated, fewer than 10% of asci abort, whereas up to 70% or more of the asci abort when inbred strains are mated to each other. We conclude that the degree of genetic relatedness of the two haploid parents determines whether abortion occurs. Progeny tests indicate that several genes are involved; the simplest interpretation is that they are weak deleterious recessives whose effects must be combined to produce a high frequency of bubble asci. No ascospores survive in the aborted asci. Therefore, bubble asci cannot distort allele ratios of markers among surviving progeny. When a dominant Round-spore gene was present in one parent of a high bubble-ascus cross, none of the young bubble asci contained nonround spores. Therefore, bubble asci do not result from illegitimate fusion of two nuclei of the same mating type. Heterokaryon-incompatibility genes are not involved in producing bubble asci. No or little bubble-ascus abortion occurs in the homothallic or pseudohomothallic species of Neurospora.
Rooting patterns of Rumex species under drained conditions
Authors: Voesenek L. A. C. J. , Blom C. W. P. M.
Published: September 2008

Root development and architecture were studied in three Rumex species growing in a perforated soil system in the greenhouse. Distinct differences in vertical root distribution under drained conditions were found among the three species. Rumex acetosa and R. palustris had a relatively superficial root pattern, whereas in R. crispus much of the root growth was concentrated in lower soil layers. In the upper soil layer the relative growth rate of the roots of R. palustris was significantly larger than that of the other species. A relation between the characteristic rooting patterns under drained conditions and the Rumex zonation in the field is discussed.
Variations des propriétés spectrales des feuilles au cours de la croissance du bouleau jaune
Authors: Messier Christian , Bellefleur Pierre
Published: September 2008

A yellow birch stand was divided into five age classes (1–5, 6–10, 11–20, 21–40, and >40 years old) to evaluate variations in spectral properties of leaves during the growth of yellow birch. Shade leaves of 1 to 5 year-old seedlings absorb significantly less, while they reflect and transmit significantly more than shade leaves of the other age classes in the 390–725 nm wavelength range. Absorptance differences are more striking in the green and the yellow between 501 and 590 nm (0.067–0.091) than in the orange and the red between 591 and 700 nm (0.041–0.054) and the violet and the blue between 401 and 500 nm (0.017–0.020).
The pattern of winter respiratory response to temperature, moisture, and freeze–thaw exposure in Bouteloua gracilis dominated grassland soils of southwestern Alberta
Authors: Coxson D. S. , Parkinson D.
Published: September 2008

Winter respiratory activity of soils from Bouteloua gracilis dominated grassland of southwestern Alberta was examined, both under in situ field conditions and over a matrix of defined laboratory conditions. The effect of winter thaw conditions was very pronounced on observed rates of soil surface CO2 evolution. Under conditions of diurnally fluctuating air temperatures, from ca. −18 to +8 °C, soil surface temperatures in early January ranged from ca. −12 to +4 °C, while concurrently measured respiratory activity ranged from less than 2 to over 16 mg CO2∙m−2∙h−1. By early spring, soil surface heating was even more extreme as a result of the greater magnitude of midday insolation exposure, with observed mean values of CO2 release ranging from less than 10 to over 60 mg CO2∙m−2∙h−1. Laboratory incubations showed continued, although low rates of respiratory activity in soils held at subzero temperatures, with a marked biphasic response pattern evident in Arrhenius plots of soil respiration. Predicted cumulative soil surface CO2 release was estimated at 34–48 g CO2∙m−2, depending on whether the effects of observed postthaw respiratory response were included. Some 55% of overall winter soil respiratory activity in the top 8 cm of the soil profile is predicted to occur at temperatures between −4 and +4 °C, with the remaining respiratory activity largely occurring at temperatures up to 15 °C. This magnitude of soil surface CO2 release represents between 3 and 30% of previously observed estimates of belowground root mass loss in the winter period, depending on whether this mass loss is presumed to occur over the entire winter period or mainly in early spring, coinciding with the peak period of root exudate production.
Sur la différenciation des trachéides dans les haustoriums d'Osyris alba parasitant Hedera helix
Authors: Benharrat H. , Renaudin S. , Rey L. , Thalouarn P.
Published: September 2008

The central part of the haustorium of Osyris alba L. contains a cambium which is continuous from the mother root to the vicinity of the "absorbing cells." It centripetally differentiates tracheary elements which make up a vascular core, the xylem bridge, connecting the vessels of the parasite root to those of the host root. In the differentiating cambial cells, a first stage of activity of the Golgi apparatus, which is related to the development of the secondary wall thickenings, is evident. This stage is marked by the presence of numerous vesicles containing an electron dense material and of multivesicular bodies lying near the plasmalemma. The cells also contain numerous spherical granules which, while being mainly proteinaceous, also contain some potassium, calcium, and sulfur. The composition of these granules, the fact that their surrounding membrane is studded with numerous ribosomes and the fact that they often form short chains in a common membranous profile lead us to conclude that they are elaborated in the endoplasmic reticulum. Later in the course of differentiation of those cells, a second stage of activity of the Golgi apparatus can be observed, with the numerous vesicles showing a light content this time. This phase precedes a lysis process during which the cells lose all their cytoplasmic content. Only the granules remain in the differentiated tracheids. [Journal translation]
La répartition des caractères dans la classification des Hamamelididae (Angiospermae)
Authors: Barabé Denis , Bergeron Yves , Vincent Gilles
Published: September 2008

By using numerical methods, the authors have analyzed correlations between vegetative and floral characters within the Hamamelididae subclass to determine which characters prevail in the characterization of each group of families. The cophenetic correlation coefficient, topological difference, cluster membership divergence, subtree membership divergence, and partition membership divergence show very little congruence between the vegetative and floral characters; this is explained by the heterobathmic evolution of the characters. In Hamamelididae, characters that best delimit groups are also those which play an important role in phylogeny. When both vegetative and floral characters indicate the same delimitations, the classification can be considered natural. The best discriminating characters at the structural level are generally the most important in a cladistic analysis because of their variability. If the character correlation principle is considered, an exhaustive analysis of the classification can help to solve phylogenetic problems.
Fixation and metabolism of carbon dioxide by photosynthetically active carrot callus cultures
Authors: Bender Ludwig
Published: September 2008

CO2 fixation experiments with photosynthetically active 3-week-old carrot callus cultures (60–90 μg chlorophyll∙g fresh weight−1) were carried out in light and darkness in nutrient solution containing NaH14CO3. Samples were taken and analyzed for labelled metabolites after 15 s and 4 min of 14CO2 fixation. The results show that in the light both the Calvin cycle and phosphoenolpyruvate carboxylation were observable, whereas in the darkness CO2 was fixed only by phosphoenolpyruvate carboxylation. However, extractable phosphoenolpyruvate carboxylation activity was reduced by about 80% upon darkening the light-grown cultures for 1.5 h.
La végétation de deux tourbières de la municipalité régionale de comté du Haut-Saint-Laurent (Québec)
Authors: Jean Martin , Bouchard André
Published: September 2008

Within a multidisciplinary study of terrestrial ecosystems of the Haut-Saint-Laurent Regional County Municipality, the vegetation of "Large Teafield" and "Small Teafield" peatlands is described from 127 stands. Detrended correspondence analysis and correlations between data indicate that the greatest vegetational variation is expressed by variables related to trophic regime (e.g., pH of peat) and moisture regime (e.g., organic content). In addition to gradient analysis, hierarchical clustering combined with reference to contingency tables is used to characterize the typology along gradients. Mapping of the community types partially relates the distribution analysis to a circular spatial pattern of the vegetation. Highly oligotrophic sites are colonized by low shrubs. Chamaedaphne calyculata is found at the centre of the peatlands, where the peat deposit is thick and fire does not play an important role. Low shrubs dominated by Betula populifolia surround the Chamaedaphne calyculata vegetation and are more affected by burning towards the perimeter. Heavily burned sites are dominated by Epilobium angustifolium. The perimeters of the peatlands are colonized by Betula populifolia or Populus tremuloides open forests, while the most stable forests are dominated by Acer rubrum. Some marshes and swamps are present where the peat deposit is thin. Sixteen community types are described for the study area.
The pattern of colony development and the formation of the uredinium of Uromyces viciae-fabae on Vicia faba
Authors: Beckett A. , Woods A. M.
Published: September 2008

Low-temperature scanning electron microscopy of frozen-hydrated specimens and transmission electron microscopy of cytochemically stained thin sections and enzymically digested samples have been used to study the pattern of colony development from the initial infection in the substomatal chamber of the leaf to the production of urediniospores within uredinia. Rapid immobilization of leaf samples by freezing enables them to be fractured, revealing information on internal structural relationships between intercellular hyphae and host cells. Extracellular matrix substances, which are well preserved by low-temperature scanning electron microscopy, play an important role in the cohesion of hyphae during the early stages of uredinium formation. Cytochemical staining indicates the presence of two such matrix materials: (i) colloidal iron-negative matrix surrounding intercellular hyphae, forming a pad between adjacent hyphal cells and (ii) a colloidal iron-positive matrix between hyphal and host cell walls. A positive reaction with colloidal iron indicates acidic mucopolysaccharides. Enzymic digestion with pronase and the staining reaction with silicotungstic acid – chromic acid suggests that a glycoprotein is present in the matrix surrounding intercellular hyphae. Possible roles for the extracellular matrix, including hyphal cohesion, cell–cell communication, and protection against desiccation, are discussed.
Wall structure and ornamentation of the urediniospores of Uromyces viciae-fabae
Authors: Woods A. M. , Beckett A.
Published: September 2008

The development of the spines and the structure and composition of the urediniospore wall of Uromyces viciae-fabae have been studied by low-temperature scanning electron microscopy, cytochemical localization, chemical, and enzymic digestion techniques. Spine formation was similar to that previously described for urediniospores of other rust fungi. Swollen collars that are distinct from the annular ridges are only evident in frozen-hydrated spores and surround the bases of spines. Pockets of endoplasmic reticulum line the periphery of spores and mark the sites of spine development. This endoplasmic reticulum may have a role in the production of enzymes and (or) structural proteins or glycoproteins. Microfibrils are present in digested and shadowed wall preparations, often associated with spines. Enzymic digestion treatment suggests that these microfibrils are chitin. Around the bases of the spines, microfibrils are orientated circumferentially and contribute in part to the thickened, annular ridges evident in all spore preparations. The spore wall matrix consists of polysaccharides. Colloidal iron staining indicates acid mucopolysaccharides. Differences in reaction of the urediniospore wall to colloidal iron at what appears to be the same stage of development suggests in situ chemical change(s), which may in turn be linked with changes in wall plasticity.
Seed-bank properties of an Appalachian sphagnum bog and a model of the depth distribution of viable seeds
Authors: McGraw James B.
Published: September 2008

Seed banks were examined in four plant communities in a high-elevation sphagnum bog in West Virginia, U.S.A. A germination assay was used to detect germinable seed densities. Vertical depth distributions were determined for one community in which the soil cores were transported intact to the greenhouse. Seed densities ranged from 12 874 in a Sphagnum-dominated community to 377 041 seeds m−2 in a sedge-dominated community. The seed bank in all communities was dominated numerically by Juncus effusus, although this species comprised a minor part of the aboveground vegetation. Three types of depth profiles were observed, including one distribution showing a simple decline in seed numbers with depth, another showing a unimodal peak below the soil surface, and a third with two distinct peaks at depth. A matrix model of seed burial was devised to account for the different depth profiles. By assuming that soil compression occurred and that the rate of compression declined with time, the model showed that either of the first two depth profiles could be produced with no need to invoke a historical change in the seed rain. The model was unable to account for the bimodal depth profile with the assumption of a constant seed rain. However, the fact that the model of seed burial could explain a unimodal peak in the depth profile suggests that simple historical interpretations of past abundance using a buried seed profile are difficult.
Effets de rayons γ 60Co sur des vitroplants haploïdes et diploïdes de Gerbera jamesonii
Authors: Dubuc-Lebreux M.-A. , Vieth J.
Published: September 2008

Gerbera jamesonii ‘Super Gerbera’ explants were irradiated in vitro with 60Co γ-rays (8–100 Gy). Some received a single dose, while others received two or three at successive multiplication cycles. Several parameters were measured after 6 weeks of in vitro culture, to compare the effects of irradiation on haploid and diploid clones. Productivity is linked to the ploidy level, whereas total growth is not. Total growth inhibition is proportionate to the given dose. Callus and plantlet growth are either inhibited or stimulated, depending on the type of treatment. Callus growth is stimulated by low doses, which induce the transformation of apices into calli; treatment of successive cycles with low doses (20 and 30 Gy for diploids, 10 and 15 Gy for haploids) ensures better plantlet development. High doses inhibited growth of calli and plantlets up to the 50% level. Variations in morphology and in chlorophyll and anthocyanin content were observed among haploid and diploid irradiated explants. Plantlet production is a good criterion for an overall evaluation. Optimal dosage to ensure 50% growth and multiplication rates is estimated at 26 Gy for diploid clones and 16 Gy for haploid clones.
Infection of different plant parts of soybean seedlings by southern Diaporthe phaseolorum and its role in the development of stem canker symptoms
Authors: Ploetz R. C. , Shokes F. M.
Published: September 2008

Leaves, petioles, petiole bases, and stems of 'Hutton' soybean seedlings (V5-V6) were inoculated with ascospores and α-conidia of southern Diaporthe phaseolorum to determine the relative importance of these plant parts as infection sites. This objective was accomplished in two experiments either by removing certain plant parts after inoculation and incubation for infection (48 h) or by protecting plant parts from infection during inoculation and incubation of plants. In both cases, plant parts were assayed for infection 48 h after inoculation and after plants had reached the R3 growth stage (66 and 56 days after inoculation for experiments 1 and 2, respectively); symptom development was rated at the end of each experiment. Significant, positive correlations were detected between the incidence and severity of symptoms and the infection of either stems 48 h after inoculation (P < 0.01 and 0.05, respectively) or petiole bases at the end of the experiments (P < 0.001 and 0.01, respectively). Development of symptoms was not significantly correlated (P ≥ 0.05) with infection of petioles, petiole bases, or leaves 48 h after inoculation. These results suggest an important and causal role for infection of petiole bases and stems in the development of the symptoms of this disease. Leaf infection appears to be unimportant in the stem canker disease cycle in the southeastern United States.
Effects of gene dosage on light harvesting chlorophyll accumulation, chloroplast development, and photosynthesis in wheat (Triticum aestivum)
Authors: Freeman Thomas P. , Duysen Murray E. , Williams Norman D.
Published: September 2008

The CD3 mutation is known to be located in chromosome 7D. CD3 plants were crossed with monosomic ‘Chinese Spring’ plants. The resulting F1 plants were selfed to yield the F2 with varying ratios of dominant to recessive genes. Chlorophyll accumulation increased and the chlorophyll a/b ratio decreased as the dominant to recessive gene ratio increased. With a decrease in dominant genes the electron transport rate increased. This increase was greater at high fluence than at low fluence because of a chlorophyll deficiency. Fluorescence induction curves indicated that it was the electron transport chain that was inhibited in plants with a low dominant to recessive gene ratio. These plants were also more deficient in the light harvesting pigment complexes of photosystem I and photosystem II and in the 110-kDa photosystem I protein than those having a high dominant to recessive gene ratio. As the ratio of dominant to recessive genes decreased, there was a decrease in the number of grana and in the number of thylakoids per granum.
Ecological relationships of wild rice, Zizania aquatica. 6. The effects of increases in water depth on vegetative and reproductive production
Authors: Stevenson S. C. , Lee P. F.
Published: September 2008

Wild rice (Zizania aquatica L.) suspended in plastic buckets from specially designed rafts, was subjected to increases in water depth during the submerged-leaf, first floating-leaf, second floating-leaf, and the first aerial-leaf stages. The depth was increased from an initial depth of 45 cm by 0 (control), 15, 30, or 50 cm. With the exception of the 15-cm treatment, increases in water depth resulted in decreases in total and component (root, stem, leaf) dry weights and the number of tillers on each plant. Plant height increased as the depth increased. Similar reductions occurred in the number of inflorescences per plant, the number of pedicels per plant, and the dry weights of the inflorescences. In all cases, the 15-cm treatment had higher production values than the control. The final biomass was influenced by the depth treatment, not the phenological stage when the depth increased.
Studies in the genus Xanthoconium (Boletaceae). I. New species and a new combination
Authors: Wolfe Jr. C. B.
Published: September 2008

Recent field investigations and type studies of Xanthoconium species have revealed the existence of three new taxa, Xanthoconium chattoogaensis, X. montaltoensis, and X. montanum are proposed as new. Additionally, X. affine var. reticulatum is proposed as a new combination.
Vertical distribution of fireweed, Epilobium angustifolium, seeds in the air
Authors: Solbreck Christer , Andersson David
Published: September 2008

Wind-transported seeds of Epilobium angustifolium L. were collected with suction traps mounted on a television tower in central Sweden. Average density–height profiles of seeds, up to 93 m aboveground, are presented for four 10-day periods. These data suggest that a large fraction (about 20 to 50%) of dispersing E. angustifolium seeds are more than 100 m above-ground. Many of these seeds are likely to be transported hundreds of kilometres by wind.