bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission of double-stranded RNAs in flax rust, Melampsora lini
Authors: Lawrence G. J. , Boelen M. G. , Pryor A.
Published: April 2011

Two strains of flax rust, Melampsora lini, designated strains CH5 and I, were found to possess a number of double-stranded (ds) RNAs. A third strain, LMS, lacked dsRNAs. Sexual transmission of the dsRNAs was investigated by examining the dsRNAs in progeny obtained by selling and by intercrossing strains CH5 and I. The results allow the dsRNAs in each strain to be assigned to transmission units, with strain CH5 possessing two such units (designated L and C) and strain I three units (L, A, and B). The L unit consists of a single large dsRNA (about 4800 base pairs), while the other units (A, B, and C) each consist of a set of five to seven smaller dsRNAs, which taken together, total approximately 8000–9000 base pairs. The L unit in both strains was transmitted to all sexual progeny, whereas the multisegment units, A, B, and C, were transmitted to only some of the progeny. The A and C units were transmitted only via recipient pycnia ("maternal" inheritance), but transmission of the B unit occurred through both donor and recipient pycnia. Asexual transmission did not always occur, since one of five sublines of strain I lacked the B set. The dsRNAs were shown to be "infectious," since strain LMS acquired dsRNAs when grown on the same plant as strain I.
Preliminary identification of date palm cultivars by esterase isoenzymes and peroxidase activities
Authors: Baaziz M. , Saaidi M.
Published: April 2011

Two types of crude extracts were obtained from 10 cultivars of date palm (Phoenix dactylifera L.); the Tris buffer extracts from acetone powder were assayed for peroxidase activity and the phosphate buffer extracts were subjected to polyacrylamide gel electrophoresis. The gels were stained for esterase activity using α-naphthylacetate and α-naphthylbutyrate as substrates. The cultivars were divided into four sets on the basis of their esterase isoenzyme phenotypes. These sets were further separated into their individual cultivars on the basis of peroxidase activities. The results are discussed with respect to the possible relationship of the peroxidase activity in the vascular fusariosis of date palm (Bayoud disease). This study has potential for practical application; however, some additional refinements in procedures appear necessary to reduce extraction time.
Environmental variation and the relationship among correlated quantitative traits in jack pine
Authors: Govindaraju Diddahally R.
Published: April 2011

The magnitude of direct influences of five quantitative traits and their relative changes in three open-pollinated families planted at a high density in four substrates was studied using path analysis. The relationships between diameter and total weight as well as crown length and total height were relatively consistent over environments, families, and size hierarchies but were inconsistent among other combinations of quantitative traits. Genetic, developmental, and environmental factors show both independent and cumulative effects on self-thinning. During self-thinning, the development, growth, and death process of individuals might depend upon the size and shape constraints of the phenotype and its components. A knowledge of relative flexibility of characters and their geometrical relationships may be useful in understanding the plant's channeling of environmental resources.
The effects of heat shock and inoculum density on growth and sporulation in axenic cultures of the flax rust fungus
Authors: Boasson Rosalinda , Shaw Michael
Published: April 2011

The number of mycelial colonies of Melampsora lini (Ehrenb.) Lév. was increased by a 2-h heat shock at 31 °C delivered 3 h after uredospores were seeded on a liquid medium at 17 ± 0.5 °C under axenic conditions. At 35–38 days from seeding, the ratio of the respective number of colonies in shock and nonshock treatments in 125-mL culture flasks was highest (7.5 to 22) at inoculum levels (1 to 4 × 103 uredospores cm−2) that yielded about 10 colonies per flask without heat shock; the ratio declined sharply at inoculum levels adjusted to yield either smaller or larger numbers of colonies per flask without heat shock. Sporulation (extinction at 458 nm) and protein per colony were positively correlated; were not directly affected by heat shock; were determined by colony number; increased to maxima as mean colony number per flask increased from 1 or less to from 10 to 100 in different experiments; and decreased at higher colony numbers per flask. The results indicate that heat shock promotes the initiation of colonies; that colony number determines the duration of logarithmic growth; and that increasing competition among individual colonies is the primary factor limiting growth and sporulation, whether or not the uredospore germlings are subjected to heat shock.
Automated image acquisition and morphometric description
Authors: White Richard J. , Prentice Honor C. , Verwijst Theo
Published: April 2011

Manual assembly of large morphometric data sets for investigations in population biology and biosystematics is extremely time consuming. Automated image handling allows rapid and accurate data collection and in addition makes it practicable to uncouple image acquisition and shape description. Variation can be characterized flexibly when these two phases of "scoring" are separated. Different descriptor systems can be used to describe a set of stored outlines, without having to return to the original objects. This paper introduces an integrated automated outline handling system and compares the relative performance of shape descriptor systems based on (i) landmark and perimeter measurements, (ii) chain codes, (iii) elliptic Fourier coefficients, and (iv) moment invariants. These methods were assessed by their ability to characterize the pattern of variation in a set of Betula leaf silhouettes with a hierarchical sample structure that allowed variation to be partitioned into within-tree, between-tree and between-species components. The descriptor systems using landmark and perimeter distances, elliptic Fourier coefficients, and moment invariants performed well, not only reflecting differences between species and between individual trees but also recovering the two-dimensional geometry of the within-tree sample positions. The elliptic Fourier method is judged to have performed best; the chain-code descriptor system performed poorly.
Benomyl-tolerant microfungi associated with mycorrhizae of black spruce
Authors: Summerbell Richard C.
Published: April 2011

The population of microfungi associated with mycorrhizal root tips of Picea mariana was sampled to determine which species were able to grow on isolation medium amended with the selective fungicide benomyl. Benomyl significantly favoured the isolation of soil Zygomycetes, including members of the genera Mortierella and Micromucor, but inhibited the growth of most soil fungi of ascomycetous affinities. Since some of the inhibited taxa, e.g., Trichoderma spp., are potential inhibitors of mycorrhiza formation in vivo, these results may explain instances where the application of benomyl has been shown to increase mycorrhiza formation in the field.
A new method for estimating horizontal growth of the peat mat in basin-filling peatlands
Authors: Kratz Timothy K.
Published: April 2011

A newly developed technique was used to determine the long-term horizontal growth rate of the peat mat in Fallison Bog, a poor fen in northern Wisconsin. This technique consisted of carbon-dating material that was alive when the lake edge was at a particular location in the peatland and then measuring the distance from that location to the current lake edge. In Fallison Bog, Chamaedaphne calyculata stems currently buried at the mat peat – debris peat interface were alive when the lake edge was at that horizontal location. Radiocarbon dates of stem material from six locations in the peatland were used to estimate when the lake edge was at each location. To calculate the average long-term horizontal growth rate, the slope of the least-squares linear regression of distance from lake edge versus age of stems was computed. The estimated rate in Fallison Bog was 2.5 cm/year (95% confidence interval was 1.6–3.5 cm/year). The linear regression explained 95.6% of the variance in the data. The author suggests that this technique may be applicable in peatlands bordering acid lakes throughout northeastern North America.
Precise configuration of the chytrid zoospore
Authors: Barr Donald J. S. , Désaulniers Nicole L.
Published: April 2011

By matching serial sections from the flagellum to the kinetosome in selected species of chytrids (Chytridiales), the kinetosome triplets have been assigned numbers that correspond to the numbers given by general convention to the flagellum doublets. The various organelles in the zoospore are located in nine longitudinal segments that lie proximal to the kinetosome. Each segment is delineated by the cartwheel spokes of the kinetosome; segment 1 lies between subfibers A of triplets 1 and 2. In Rhizophydium chlorogonii Jaczewski, R. granulosporum Scherffel, Chytridium confervae (Wille) Minden, and Chytriomyces hyalinus Karling, the rootlet extends from between kinetosome triplets 1 and 2, but at different angles in each species. In Catenochytridium hemicysti Knox the rootlet extends from the triplet 1, and in Allochytridium luteum Barr & Désaulniers between triplets 9 and 1. In all species the center of the rumposome is located in segments 8, 9, or 1, and the nucleus in segments on the opposite side. The nonfunctional centriole is connected by fibers that extend from kinetosome triplets 6–7 in all species and also from triplets 5 and 8 in some species.
Above- and below-ground macrophyte production in Scirpus tidal marshes of the St. Lawrence estuary, Quebec
Authors: Giroux Jean-François , Bédard Jean
Published: April 2011

Above- and below-ground standing crops as well as primary production of several macrophytes were estimated in Scirpus marshes along the south shore of the St. Lawrence River estuary in Quebec. Aboveground standing crop was measured by clipping vegetation, while belowground standing crop was estimated by soil coring. Seasonal variation of live and dead standing crops was first determined for different plant species. The root:shoot mass ratio was then examined and related to the life history of each species. Total aboveground production varied from 74 to 627 g ash-free dry mass∙m−2∙year−1 among different plant communities, whereas belowground production was lower, with estimates varying between 38 and 244 g∙m−2∙year−1. Production was lower along the St. Lawrence estuary than in other types of marshes located farther south.
Microhabitat comparisons of transpiration and photosynthesis in three subalpine conifers
Authors: Carter Gregory A. , Smith William K.
Published: April 2011

Differences in water and photosynthetic relations were compared for three codominant conifers (Engelmann spruce (Picea engelmaniï), subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) at microhabitats within a subalpine forest (central Rocky Mountains, U.S.A.) that were considered representative of different successional stages. Diumal measurements of photosynthesis, leaf conductance, and transpiration were taken at microhabitats considered early-successional (open), intermediate (forest gap), and late-successional (forest understory) environments to evaluate possible influences of gas-exchange physiology in observed distributional and successional patterns. Pine had greater water-use efficiency (photosynthesis/transpiration) in early- versus late-successional environments, primarily as a result of a lower leaf conductance and transpiration. Photosynthetic performance was similar among all three species at each respective microhabitat and increased as the openness of the microhabitat increased. Greater water-use efficiency may significantly improve the growth of pine over spruce and fir on more open, drier sites at lower elevation. Higher transpiration in spruce and fir may limit these species to higher elevation sites, to understory sites at middle elevations, and to moister open sites at lower elevations (e.g., riparian sites).
Mineral storage in Cucurbita embryos. I. Calcium storage in relation to embryo size
Authors: Ockenden I. , Lott J. N. A.
Published: April 2011

Cucurbita maxima cv. Warted Hubbard has large fruits up to 10 kg in weight and its seeds have an average weight of about 0.25 g. Cucurbita andreana has fruits < 1 kg in weight and its seeds have an average weight of about 0.02 g. Within each species fruit weight was highly variable, while seed weight was quite stable. The overall range of variation in seed weight within both species was about 2.5-fold. Embryos of the species with the small seeds (C. andreana) contained less Ca on a per embryo basis than did those of C. maxima, but on a per gram basis these small embryos contained three times more Ca than the larger C. maxima embryos. Within C. maxima embryos, Ca varied as much as fivefold, with heavy and long embryos tending to have less Ca per gram tissue than smaller C. maxima embryos. Calcium concentrations within C. andreana were not correlated with embryo size.
Perte de compétitivité par adaptation au milieu physique: cas du Salix uva-ursi dans la toundra du Nouveau-Québec
Authors: Maillette Lucie , Bélisle Luc , Seguin Maurice K.
Published: April 2011

Plant species of wind-exposed tundra sites are usually low lying and slow growing. Such a combination probably reduces competitive ability, perhaps to the point of limiting wind-tolerant species to sites with little or no competition, i.e., the most exposed sites, as if there were a trade-off between adaptation to physical conditions and competitive ability. That hypothesis was tested with Salix uva-ursi Pursh, an arctic–alpine species common on windy sites in northern Quebec. Salix uva-ursi increases in abundance with exposure to wind, contrary to other species, but tolerates, even "prefers", the physical conditions found in sheltered sites. These two observations support the idea that interspecific competition limits the distribution of S. uva-ursi. However, the vigour of S. uva-ursi (number and size of shoots) is greatest in the sheltered sites, where the other species are more numerous and vigourous. This apparent contradiction between distribution and vigour could find an explanation in the temporal variations in climate. Under favourable conditions, prostrate and slow growth would be a handicap to S. uva-ursi, compared with other species, whereas under harsh conditions, species sensitive to wind and cold would suffer more than S. uva-ursi. [Translated by the journal]
The effect of glyphosate on resistance of tomato to Fusarium crown and root rot disease and on the formation of host structural defensive barriers
Authors: Brammall R. A. , Higgins V. J.
Published: April 2011

Colonization of root tissues in tomato seedlings genetically resistant to Fusarium oxysporum f.sp. radicis-lycopersici Jarvis & Shoemaker occurred following exposure to a sublethal concentration of the herbicide glyphosate (1.0 mM for 24 h prior to inoculation). The glyphosate-induced colonization was associated with an inefficiency in incorporation of phenolic materials into the papillae and into the modified cortical cell walls normally formed in response to this pathogen. Glyphosate-induced susceptibility decreased when the glyphosate was applied at 24 or 48 h after inoculation. Plants supplied with exogenous L-phenylalanine failed to exhibit reduced susceptibility after glyphosate exposure. In radial growth bioassays, growth of the fungus was unaffected by 4.0 mM glyphosate. α-Aminooxyacetic acid, an inhibitor of phenylalanine ammonia lyase, also increased the severity of the disease in resistant plants. Glyphosate also induced susceptibility to an isolate of F. solani f.sp. pisi, which was normally not pathogenic to tomato.
Effects of donor genotype and bud sampling on microspore culture of Brassica napus
Authors: Chuong P. V. , Deslauriers C. , Kott L. S. , Beversdorf W. D.
Published: April 2011

The effects of genotype, intravarietal donor plants, planting density, inflorescence age, bud position, and bud developmental stage on embryo production in Brassica napus L. were investigated. Embryo yields, frequency of normal embryo production, and direct plantlet regeneration were genotype dependent. Embryo yield ranged from 4 to 196 embryos/anther equivalent, normal cotyledonous embryos varied from 6 to 72% of total embryos produced, and direct plantlet regeneration from embryos occurred from 1 to 47% of embryos subcultured. The G231 line was superior in all three factors Embryo production also was affected by the physiological condition of individual donor plants. Dense plantings reduced plant and bud size, leading to reduced microspore production. In some genotypes embryo production was affected negatively at dense planting densities (3 plants/pot), while in others the rate was unchanged, the plants maintaining high embryogenic potential. The highest frequency of embryogenesis was obtained from cultures of buds sampled at approximately 1 week after first flowering and decreased with the aging of the inflorescence. Buds from 2-week-old inflorescences produced fewer embryos and these were generally small, multilobed structures that never developed further into plants. Buds from the lateral racemes and from the primary raceme appeared to be equally capable of embryo production if selected at the appropriate stage of development. Embryogenic microspores commonly were found in buds with a petal/anther length ratio between 1/4 and 3/4, although the optimum embryo yield was from microspores of buds around the 1/2 ratio. Microspores from later bud stages became oval in culture and did not develop further, while uninucleate microspores remained round, and enlarged prior to division.
Cytological aspects of isolated microspore culture of Brassica napus
Authors: Kott L. S. , Polsoni L. , Beversdorf W. D.
Published: April 2011

Preculture cytological events within anthers of two genotypes of Brassica napus were examined to detect differences between microspores that have embryogenic potential and those that do not. Microspores of five anthers per bud were cultured, while the sixth anther was fixed for cytological observation. A series of buds of increasing maturity were individually sampled from specific racemes. Correlations of bud, anther, microspore, and nuclear size were drawn to establish physical parameters for each cytological stage. Cytological events and cytophotometrically monitored DNA content were noted for spores of each anther size class. Best embryogenic responses were among populations of microspores in the late uninucleate stage, immediately prior to first pollen mitosis. Typical, rod-shaped, cotyledonous embryos could be generated within 30 days from microspores at this stage at a rate up to 1300/anther. Slightly younger or older microspores had a drastically reduced embryogenic performance. Postculture observations (within 6 h after culture) indicated that the embryogenic spores appeared spherically swollen, distinctly vacuolate, and with a clear cytoplasm.
Correlation between protonema morphogenesis and the development of the microtubule system in Funaria spore germination under normal conditions and at high auxin concentrations: an immunofluorescence study
Authors: Ljubešić N. , Quader H. , Schnepf E.
Published: April 2011

Ungerminated spores of Funaria do not contain distinct microtubules but show diffuse antitubulin antibody fluorescence. The microtubules arise when, 24–48 h after sowing, the spores are swollen and the first germ tube begins to protrude. Initially, diffuse fluorescence and microtubules are concentrated around the nucleus. Treatment with auxin at high concentrations (5 × 10−5 – 10−4 M) retards germination and cell division. Like antimicrotubule agents, such as colchicine and chloroisopropyl-N-phenylcarbamate, high auxin concentrations affect the formation of microtubules; either short, irregularly shaped microtubules and fluorescent spots arise, or there is no evidence of microtubules. The auxin effects on growth and microtubules can be reversed in less than 1 day. There is a correlation between the formation of the microtubule system and cell morphogenesis.
IAA biosynthesis by the ectomycorrhizal fungus Hebeloma hiemale as affected by different precursors
Authors: Gay G. , Rouillon R. , Bernillon J. , Favre-Bonvin J.
Published: April 2011

The effect of different precursors, aromatic amino acids, or intermediates of the shikimate pathway (pathway for aromatic amino acids biosynthesis), on indole-3-acetic acid (IAA) synthesis by the ectomycorrhizal fungus Hebeloma hiemale was studied. This fungus did not release detectable amounts of IAA when cultivated on a medium containing no precursor or supplemented with 1 mM phenylalanine, 1 mM tyrosine or 1 mM shikimic acid. IAA accumulation in culture filtrates was low (0.5 μmol per flask) when the medium was supplemented with 1 mM anthranilic acid. The fungus released 1.6 μmol of IAA when cultivated on a medium containing 1 mM indole and 6.9 μmol in the presence of 1 mM tryptophan. These results were confirmed by studying the ability of crude enzyme extracts to convert these precursors to IAA. Specific IAA synthesizing activity was of the same order when indole or tryptophan were used as precursors. The comparison of in vivo and in vitro activity of IAA synthesizing enzymes demonstrated that a need for tryptophan concentrations higher than 0.1 mM to obtain detectable IAA synthesis is due to the low ratio of tryptophan breakdown into IAA. The inability of H. hiemale to synthesize IAA in the absence of precursors or in the presence of shikimic acid may be ascribed to a very poor endogenous tryptophan accumulation in the hyphae due to feed back inhibition of the anthranilate synthetase by tryptophan. These results indicate that precursor availability in root exudates is probably one of the main limiting factors for IAA release by ectomycorrhizal fungi under symbiotic association. Key words: ectomycorrhizal fungus, Hebeloma, indole-3-acetic acid, tryptophan, indole, shikimate pathway.
A scanning electron microscope study of the internal structure of mature linear mycelial organs of four basidiomycete species
Authors: Cairney J. W. G. , Jennings D. H. , Veltkamp C. J.
Published: April 2011

The internal structure of mature mycelial cords of Lycoperdon pyriforme, Mutinus caninus, Steccherinum fimbriatum, and Tricholomopsis platyphylla was studied using scanning electron microscopy. Although interspecific differences in the degree of internal differentiation were observed, linear mycelial organ structure in all four species was similar, in that they consisted of a cortex of fine hyphae surrounding a medulla containing large diameter "vessel" hyphae. Based on similarities between the internal structure of rhizomorphs of Armillaria mellea and the mycelial cords of the species considered in this study, the exclusive use of the term "rhizomorph," qualified by adjectives describing development at the growing front and the degree of internal differentiation, is proposed in describing all linear mycelial aggregates.
Phylogeny and reclassification of the tribe Inuleae (Asteraceae)
Authors: Anderberg Arne A.
Published: April 2011

The tribe Inuleae Cass. has been subject to a critical investigation. The many technical characters that are traditionally used in classification of the Inuleae are scrutinized, discussed, and analysed by means of a computerized parsimony program (PAUP). With one representative from each of the tribes Vernonieae, Liabeae, and Lactuceae as outgroups, three different analyses have been performed. Strict consensus trees for the three separate analyses are presented and discussed. A consensus tree based on the cladogram topologies obtained from all the three analyses is also presented. The taxonomic implication of the analyses is that the tribe Inuleae is an unnatural, not monophyletic group, which must be divided in better defined monophyletic tribes. Hence, three tribes are recognized and the majority of the described genera of the Inuleae are tentatively referred to one of these tribes. The tribes Gnaphalieae Rydb. (comprising the Inuleae–Gnaphaliinae and the Inuleae–Athrixiinae sensu Merxmüller et al.) and the Inuleae s.str., are accepted. Furthermore, the former subtribe Inuleae–Plucheinae Benth. is recognized and described as the new tribe Plucheae (Benth.) A. Anderb.
Calonectria avesiculata sp.nov.
Authors: Schubert T. S. , El-Gholl N. E. , Alfieri Jr. S. A. , Schoulties C. L.
Published: April 2011

Calonectria avesiculata T. S. Schubert, N. E. El-Gholl, S. A. Alfieri Jr., et C. L. Schoulties sp.nov. is described from leaf spots on Ilex vomitoria Ait. in Florida.
Cytological studies of the infection process in nodulating and nonnodulating pea genotypes
Authors: Gal M. F. Le , Hobbs S. L. A.
Published: April 2011

Pisum sativum L., cv. Afghanistan, does not form nodules with 128C52, a North American strain of Rhizobium leguminosarum. Timing of the abortion of the nodulation process was determined by microscopy in both 'Afghanistan' and nonnodulating 'Trapper,' produced by backcrossing the nonnodulating genes of 'Afghanistan' into 'Trapper,' a North American variety. Three to 5 days after inoculation, we observed deformed roots and localized swellings as well as loosely curled root hairs in these nonnodulating combinations. Rhizobia entered root hairs and epidermal cells, but no infection threads were seen. Cortical cells divided and a nodule meristem was initiated. Some meristematic cells showed abnormal features such as a high concentration of free ribosomes, dilated endoplasmic reticulum often connected to a dilated nuclear envelope, and disrupted mitochondria. Cortical cells around the nodule meristem were devoid of starch grains. Such phenotypes are known to be associated with rhizobial mutants, but in this case a plant effect is responsible.
Ultrastructure of the septum in Ballocephala verrucospora (Entomophthorales, Zygomycetes)
Authors: Saikawa Masatoshi
Published: April 2011

A tardigrade parasite, Ballocephala verrucospora Richardson (Entomophthorales, Zygomycetes), has septa with a central perforation between conidia and unicellular conidiiferous branchlets, and between the branchlets and nonseptate conidiophores. The septum seen in ultrathin sections, cut transversely through the median part of the septal wall, showed a bifurcately flared configuration around the central perforation that encloses a plug with moderate electron opacity. Although the bifurcation of the B. verrucospora septum is always distorted, the septal structure is very similar to those produced by Kickxella alabastrina Coemans (Kickxellales, Zygomycetes) and Harpella melusinae Léger & Duboscq (Harpellales, Trichomycetes); this was also observed in the present study. When the B. verrucospora conidia are liberated from the conidiiferous branchlets, the branchlets rupture completely and the bifurcate septa can no longer be observed.
Tricholoma, subgenus Tricholoma, section Albidogrisea: North American species found principally in the Great Lakes region
Authors: Ovrebo Clark L.
Published: April 2011

Fifteen species of Tricholoma, subgenus Tricholoma, section Albidogrisea, are described and illustrated. All species occur in the Great Lakes region and many are distributed elsewhere in eastern North America. Four species are new: Tricholoma argenteum, Tricholoma atrodiscum, Tricholoma insigne, and Tricholoma pullum. Keys are provided to the sections of subg. Tricholoma and to the species and stirpes of sect. Albidogrisea.
Vascular flora and phytogeography of Cape Prince of Wales, Seward Peninsula, Alaska
Authors: Kelso Sylvia
Published: April 2011

Cape Prince of Wales on the western tip of the Seward Peninsula in Alaska is the closest point in continental North America to Asia. From here the eastern tip of the Chukotsk Peninsula is less than 80 km away across the Bering Strait. Owing to the position of the Seward Peninsula, its flora is of great biogeographic interest, yet until recently was poorly known because of the remoteness of the region. Here I document the 292 vascular plant taxa that compose the flora at Cape Prince of Wales. I consider this Bering Strait region a distinct phytogeographic zone. The flora has strong alpine affinities, and it is marked by the local abundance of certain Asiatic and Beringian species, and the absence of continental species requiring summer warmth that are common elsewhere on the Seward Peninsula.
Isometric virus-like particles encapsidate the double-stranded RNA found in Puccinia striiformis, Puccinia recondita, and Puccinia sorghi
Authors: Dickinson Matthew J. , Pryor A.
Published: April 2011

Isolates of Puccinia striiformis (wheat stripe rust), Puccinia recondita (wheat leaf rust), and Puccinia sorghi (maize rust) contain complexes of double-stranded RNA. In each species, there are at least 12 double-stranded RNAs ranging in size from 150 to 5000 base pairs, and the number, size, and quantitative relationships between the double-stranded RNAs are distinctive for a given species. Most, if not all, of the double-stranded RNAs in each species can be extracted from isometric virus-like particles of 40 nm in diameter purified by sucrose and (or) Cs2SO4 gradients. The data indicate that in these three species of Puccinia the double-stranded RNAs are encapsidated in virus-like particles.
Amino acid content of water-stressed plantlets of Populus tremuloides clones in relation to clonal susceptibility to Hypoxylon mammatum in vitro
Authors: Bélanger R. R. , Manion P. D. , Griffin D. H.
Published: April 2011

Plantlets from five clones of Populus tremuloides were cultured in media at three different osmotic potentials to assess the effects of water stress on amino acid content. Differences in amino acid content were then related to differences in susceptibility (determined in a previous study) of clones to Hypoxylon mammatum. Changes in amino acid concentrations varied among the amino acids. Alanine, arginine, asparagine, glutamine, glutamate, and proline increased generally but not consistently among all clones. Comparisons among the clones for these six amino acids showed significant variations. Proline, which has been shown to accelerate radial growth of H. mammatum more than other amino acids, increased progressively with increased water stress in all clones. Levels of proline among the clones were correlated (r = 0.89) with susceptibility to infection and colonization of the clones by H. mammatum. Alanine and glutamine were also similarly correlated with infection rating. However, one clone, which grew poorly in culture, did not show this relationship. In comparison with the other clones, it had low levels of all amino acids, which did not increase significantly in response to water stress. Yet in the inoculation study, it had the highest infection rating at all stress levels, suggesting that other stress-induced factors are also important. These results suggest that nitrogen status of some aspen clones under water stress may increase their susceptibility to hypoxylon canker.
Lichen physiology and air pollution. I. Physiological responses of in situ Parmelia sulcata among air pollution zones within Biel, Switzerland
Authors: Arb C. von , Brunold C.
Published: April 2011

Parmelia sulcata, a rather pollution resistant lichen species, was collected at 13 locations with different levels of air pollution from its natural habitat in the city and the suburbs of Biel, Switzerland, The growth rate, net and gross photosynthesis, release of C-assimilates, dark respiration, and protein and chlorophyll content were determined. Growth rates differed maximally by a factor of 7 with the lowest rates at fee central and most polluted locations of the city. The chlorophyll content was highest in the center and maximally four times lower at the suburban locations. The protein content, dark respiration, and net and gross photosynthesis did not differ significantly between the 13 locations when based on the dry weight, but the percentage of C-assimilates released by the algal cells was up to 15 times lower in the center. These results are different from previous reports where the transplant technique had been used, indicating that the long term effects of air pollution on the lichen metabolism under natural conditions are not the same. Key words: photosynthesis, C assimilation, growth, chlorophyll, dark respiration.
Les plastes des cellules-hotes des mycorhizes à vésicules et arbuscules
Authors: Dexheimer Jean , Gérard Joëlle , Boudarga Khadua , Jeanmaire Christine
Published: April 2011

In nonmycorrhizal roots, the plastids of cortical cells developed either into leucoplasts (Plectranîhus australis) or into amyloplasts (Prunus avium and Pirus malus). In cells infected with the endophyte of vesicular-arbuscular mycorrhizas, in all three species studied, the plastids were very long secretory leucoplasts with a well-developed stromatic tubular net. In woody Rosaceae, the absence of starch is thought to result from a disturbance in carbon metabolism caused by the endophyte. Differentiation into secretory leucoplasts with a stromatic tubular net may be the expression of a defense reaction.
Comportement méiotique chez des plantes de Luzerne (Medicago sativa) provenant d'une expérience de fusion somatique
Authors: Coulaud Joëlle , Siljak-Yakovlev Sonja , Téoulé Evelyne
Published: April 2011

The meiotic behaviour of two tetraploid (2n = 32) clones of alfalfa and their progenies, issued from sexual reproduction (2n = 32) or somatic hybridization (2n = 64, 48, 32… ), has been studied. Meiosis, in all the plants, always displays perturbations, but they have limited consequences on the production and viability of pollen in parents and sexual hybrids. Somatic hybrids and plants issued from protoplast fusions within one clone are octoploids (2n = 64) and produce a large array of abnormal tetrads, giving rise to variable ploidy levels in pollen grains. Most of the pollen remains viable. One of the somatic hybrids lost a set of chromosomes and became hexaploid (2n = 48) after propagation by cuttings. Its meiosis is strongly disturbed and produces many abnormal cells. However, the amount of viable pollen remains high. All the other plants obtained by somatic hybridization are tetraploid and not like the hybrid type, but falcata. One of them is hyperaneuploid (2n = 33) and the additional chromosome does not seem to be eliminated during meiosis: 50% of the young pollen may contain 17 chromosomes. Another plant, which was octoploid and then became tetraploid, frequently produces abnormal pollen with reduced viability. Most of the regenerated plants look like one of the parents. Interestingly, some of the plants, which are unique in terms of their mode of production and their characteristics, are not only male-fertile, but also likely to supply a very varied assortment of gametes. The introduction of the fertile plants in breeding programs is expected.
Litter decomposition under snow cover in a balsam fir forest
Authors: Taylor Barry R. , Jones H. Gerald
Published: April 2011

In a subalpine balsam fir forest in Quebec, Canada, mass losses, respiration rates, and nitrogen and sulphur dynamics were measured on fir needles, birch leaves, lichens (mixed species), and small twigs decomposing under deep (> 1.5 m) winter snow for 6 months. Mass losses ranged from <6% (twigs) to 70% (lichens) and relative decomposition rates of needles and leaves were reversed from those expected at higher temperatures. Isolation of fir needles from direct contact with the snow did not affect decay rate, nor was decay accelerated by spring snowmelt. In situ respiration rates increased from about 1 mg CO2/(g∙day)) in February to 3–5 mg CO2/(g∙day)) in May, mostly because of rising temperatures. Summer respiration rates were much higher (> 6 mg CO2/(g∙day)). Nitrogen and suphur concentrations increased in all nonwoody litter over winter, but only birch leaves and some fir needles appeared to assimilate nutrients from the environment. Melting snow could easily have provided all of the nitrogen and sulphur taken up by decomposing litter. Decomposing lichens released 40 and 60%, respectively, of their initial nitrogen and sulphur contents. A literature review indicates mass losses from leaf litter decomposing under deep snow vary according to the proportion of labile material in the litter and usually constitute 40–60% of total first-year mass losses. Key words: decomposition, winter, balsam fir, snow.
Identification des futures cellules procambiales au cours de l'initiation foliaire chez Lycopersicon esculentum
Authors: Hernández Mercédes Niebla , Driss-École Dominique
Published: April 2011

In Lycopersicon esculentum, the cells at the origin of the procambium were identified after [3H]thymidine incorporation and high-resolution autoradiography. They were identified by their position, which consists in a selective area found at the edge of the already differentiated procambium, and by their ability to synthetize DNA. These cells synthetize DNA synchronously with those which edify the leaf buttress and they are present before the first superficial mitoses of leaf initiation.
Life history and vegetative reproduction in Carex
Authors: Bernard John M.
Published: April 2011

The genus Carex is made up of about 2000 species of herbaceous perennials occurring in a wide range of habitats throughout the world but especially in north temperate and arctic regions. They are modular organisms that reproduce vegetatively by rhizomes or other means, some species forming extensive and long-lived clones, others tufts, clumps, or tussocks of various sizes. Most temperate and arctic species have shoots formed during the previous year, some emerging in autumn, others remaining below ground until spring. The maximum shoot life span for temperate species appears to be approximately 24 months but mortality is very high; sometimes 90% of shoots do not live for the whole 2-year life span. Snoots in arctic-alpine regions live longer, perhaps as long as 5–7 years, with lower mortality. Mortality is caused by differences in time of emergence, flowering, animal grazing, the age of the genet, and internal competition through the rhizome system.
Medicago syriaca, a new species
Authors: Small Ernest
Published: April 2011

Medicago syriaca is described as a new species of Medicago section Spirocarpos subsection Pachyspirae. This is based on a single Syrian population that is distinguishable by a combination of characters from its allies.
Effect of chemical and heat therapy on virus concentrations in in vitro potato plantlets
Authors: Griffiths Helen M. , Slack Steven A. , Dodds John H.
Published: April 2011

Potato (Solanum tuberosum) plantlets were established in vitro to evaluate the effectiveness of chemicals and heat therapy for antiviral activity. Ribavirin was shown to be the most active chemical. Further studies were performed in which plantlets established from nodal cuttings were exposed to an alternating 4-h cycle of 35–31 °C and ribavirin (20 mg/L) therapy for 4 weeks, and then tested quantitatively for virus titer by the enzyme-linked immunosorbent assay. Plantlets were further propagated via nodal cuttings at room temperature without exposure to ribavirin. Virus assays were performed and virus-free plantlets were grown out as mature plants for a final virus assay. Ribavirin alone or in combination with heat therapy was effective in reducing potato virus M, S, and X titers (between 10- and 60-fold). Virus-free plants were obtained from both treatments. For potato viruses Y and leafroll, about a fourfold reduction in titer was observed after the ribavirin–heat treatments. When multiple viruses were present, quantitative (10- to 20-fold) reductions in potato viruses M, S, X, and leafroll were observed and resulted in plants free of potato viruses M, S, and X. This protocol enables the investigator to quantitatively monitor the impact of a single variable on the virus–host interaction. We have also been able to demonstrate that virus elimination can be obtained without a requisite meristem-tip excision step.
Ecological relationships of wild rice, Zizania aquatica. 9. Production in organic–flocculent sediments
Authors: Day W. R. , Lee P. F.
Published: April 2011

Season chemical trends and wild rice production were examined in unproductive organic–flocculent sediments from three lakes. Variations occurred in the level of organic matter and nutrient concentrations among these lakes. However, these among-lake variations were not as distinct as the differences that occurred between these lakes and a productive wild rice lake. The three organic–flocculent lakes exhibited similar poor wild rice production, retarded phenological development, and red colouration on wild rice stems and leaves. Although nutrient variations did occur among the organic–flocculent lakes, it was hypothesized that a common limiting factor was affecting wild rice production in this type of sediment. Key words: Zizania aquatica, nutrients, phosphorus, sediment, primary production, establishment.
Sympodial and monopodial branching in Acer: implications for tree architecture and adaptive significance
Authors: Sakai Satoki
Published: April 2011

To understand the adaptive significance of sympodial and monopodial branching in Japanese Acer, growth patterns of leader shoots of vigorous saplings and their consequences for tree architecture were examined in 6 sympodial species (exhibiting sympodial branching) and 14 monopodial species (exhibiting monopodial branching). All sympodial species were characterized by weak dominance of a main lateral branch and its large branching angle with the leader branch it developed (referred to as the SS type). The monopodial species were divided into two types. One, the ME type, was characterized by strong dominance and a small branching angle of a terminal branch, and the other, the MS type, by intermediate dominance and a small branching angle. The computer simulations showed that the growth pattern of the SS type would result in a vigorous sapling with many horizontally spread branches, that of the ME type with a large amount of vertical growth, and that of the MS type with an intermediate architecture between these two types. The SS, MS, and ME types were recognized as strategies adapted to less sunny, intermediate, and more sunny sites, respectively.
A new Nodulosphaeria contrasted with N. olivacea and Leptosphaeria erigerontis
Authors: Shoemaker R. A. , Babcock C. E.
Published: April 2011

A new species of pyrenomycete, Nodulosphaeria edgari, is described from western Canada and western U.S.A. A closely related species, Nodulosphaeria olivacea (Ellis) L. Holm, is redescribed from the lectotype and additional collections from western U.S.A. The two species sometimes occur together on the same host plant material. Nodulosphaeria edgari was previously reported from western U.S.A. under the misapplied names Leptosphaeria erigerontis (Berlese) Berlese and Nodulosphaeria olivacea. Species concepts are stabilized based on type studies of the three taxa. Host plant and geographic records are revised.
Early effects of the ectomycorrhizal fungus Paxillus involutus on the root rot organism Fusarium associated with Pinus resinosa
Authors: Farquhar M. L. , Peterson R. L.
Published: April 2011

Infection of Pinus resinosa Ait. seedlings in a sterile test tube culture system by Fusarium oxysporum f.sp. pini Schlecht. emend. Snyd. & Hans., which was determined microscopically by the presence of the fungus within root tissues, was significantly reduced within the first 6 days of infection after prior inoculation with the ectomycorrhizal fungus Paxillus involutus (Batsch) Fr. Hyphae and conidia of the pathogen were swollen and filled with osmiophilic material when P. involutus was also present in the rhizosphere of P. resinosa seedlings. Germination of F. oxysporum conidia was suppressed when they were placed in holes in P. involutus cultures on modified Melin Norkrans medium in Petri plates but was restored with removal of conidia from plates. Suppressed, ungerminated conidia had thick cell walls and large cytoplasmic inclusions. Staining using Calcofluor White M2R New revealed changes in the binding properties of septal wall material. Key words: Paxillus, Fusarium, ectomycorrhiza, disease suppression, anatomy.
Cytokinins and abscisic acid in hardening winter wheat
Authors: Taylor John S. , Bhalla Munjeet K. , Robertson J. Mason , Piening Lu J.
Published: April 2011

During overwintering in a northern climate, winter wheat goes through a hardening process, followed by dehardening in late winter – early spring. This sequence of events may be partially controlled by changes in endogenous hormone levels. Crowns and leaf tissue from field grown winter wheat (Triticum aestivum L. cv. Norstar) seeded at the beginning of September were collected and freeze-dried at monthly intervals during the winters of 1985–1986 and 1986–1987. Material was also sampled and freeze-dried from seedlings grown in a growth chamber under hardening conditions (21 °C for 2 weeks plus 3 °C for 6 weeks) or nonhardening conditions (3 weeks at 21 °C). The tissues were analysed for cytokinins and abscisic acid. Cytokinin levels, measured with the soybean hypocotyl section assay, declined from October onwards and then rose to a peak in late winter (January and February, winter 1986–1987; February and March, winter 1985–1986), subsequently declining again. Abscisic acid, quantitated as the methyl ester by gas chromatography with an electron capture detector, increased in level from October to December, then decreased to a relatively low level between January and March. Hardened seedlings from the growth chamber contained significantly higher abscisic acid levels and significantly lower cytokinin levels than did the nonhardened seedlings. Key words: abscisic acid, cytokinins, hardening, Triticum aestivum, winter wheat.
Changes in respiratory metabolism during sprouting of aged seed-potato tubers
Authors: Mikitzel Loretta J. , Knowles N. Richard
Published: April 2011

Seed-potato tubers stored for more than 8 months lose apical dominance and sprout with reduced vigor compared with younger tubers. To determine if age-reduced vigor is associated with less efficient respiratory activity, contributions of the different modes of respiration were measured in tissue from 7- and 19-month-old tubers at 6-day intervals over an 18-day sprouting period. Although respiration rate of tissue from the two tuber ages was equal at planting, it increased for both during sprouting, reaching a level 51% higher in tissue from old tubers by the end of the study. Tuber age and time had no effect on cytochrome-mediated respiration, which averaged 18 nmol O2/(min∙g fresh weight) over the study interval. However, the rate of alternative respiration of tissue from old tubers increased through day 12, reaching a level 30-fold greater than that of tissue from young tubers. As a percentage of total respiration, residual respiration was relatively constant (26%) in both ages of tissue during sprouting. In young tuber tissue, alternative respiration decreased from 9 to 1% of the total by day 12. Over the same period, the proportion of alternative respiration in old tissue increased from 14 to 28%, and this occurred with a concomitant decrease in the proportion of cytochrome-mediated respiration. During sprouting, old tubers appeared to be generating higher levels of ATP through a combination of the cytochrome-mediated and alternative pathways compared with young tubers; however, the increased energy-metabolizing ability of old seed tubers is less efficient at meeting the demands of sprout growth, as indicated by the lower weight of sprouts produced. Key words: potato, age-reduced vigor, respiration, sprouting.