bluuebunny/crossref_metadata_2025 huggingface dataset:
A Linear Pentapeptide Is a Quorum-Sensing Factor Required for
mazEF
-Mediated Cell Death in
Escherichia coli
Authors: Kolodkin-Gal Ilana , Hazan Ronen , Gaathon Ariel , Carmeli Shmuel , Engelberg-Kulka Hanna
Published: October 2007

mazEF
is a toxin-antitoxin module located on many bacterial chromosomes, including those of pathogens. Here, we report that
Escherichia coli mazEF
-mediated cell death is a population phenomenon requiring a quorum-sensing molecule that we call the extracellular death factor (EDF). Structural analysis revealed that EDF is a linear pentapeptide, Asn-Asn-Trp-Asn-Asn. Each of the five amino acids of EDF is important for its activity.
A Melanocortin 1 Receptor Allele Suggests Varying Pigmentation Among Neanderthals
Authors: Lalueza-Fox Carles , Römpler Holger , Caramelli David , Stäubert Claudia , Catalano Giulio , Hughes David , Rohland Nadin , Pilli Elena , Longo Laura , Condemi Silvana , de la Rasilla Marco , Fortea Javier , Rosas Antonio , Stoneking Mark , Schöneberg Torsten , Bertranpetit Jaume , Hofreiter Michael
Published: October 2007

The melanocortin 1 receptor (MC1R) regulates pigmentation in humans and other vertebrates. Variants of MC1R with reduced function are associated with pale skin color and red hair in humans of primarily European origin. We amplified and sequenced a fragment of the MC1R gene (
mc1r
) from two Neanderthal remains. Both specimens have a mutation that was not found in ∼3700 modern humans analyzed. Functional analyses show that this variant reduces MC1R activity to a level that alters hair and/or skin pigmentation in humans. The impaired activity of this variant suggests that Neanderthals varied in pigmentation levels, potentially on the scale observed in modern humans. Our data suggest that inactive MC1R variants evolved independently in both modern humans and Neanderthals.
Changes in Regulation of a Transcription Factor Lead to Autogamy in Cultivated Tomatoes
Authors: Chen Kai-Yi , Cong Bin , Wing Rod , Vrebalov Julia , Tanksley Steven D.
Published: October 2007

We report the cloning of
Style2.1
, the major quantitative trait locus responsible for a key floral attribute (style length) associated with the evolution of self-pollination in cultivated tomatoes. The gene encodes a putative transcription factor that regulates cell elongation in developing styles. The transition from cross-pollination to self-pollination was accompanied, not by a change in the STYLE2.1 protein, but rather by a mutation in the
Style2.1
promoter that results in a down-regulation of
Style2.1
expression during flower development.
THE CHROMOSOMES IN NEUROSPORA HYPHAE
Authors: Dowding E. Silver
Published: October 2007

In Neurospora tetrasperma, hyphal chromosomes, unlike those within asci, are extremely small. Their appearance and behavior is similar to that previously described by this laboratory for other Ascomycetes. They are linearly arranged, usually upon a fine filament. The filament and the chromosomes together constitute a threadlike nucleus. Double threads, in the form of a Y or X or some other configuration, are interpreted as being in division.
SCIRRHIA PINI N. SP., THE PERFECT STATE OF DOTHISTROMA PINI HULBARY
Authors: Funk A. , Parker A. K.
Published: October 2007

The perfect state of Dothistroma pini Hulbary was found on native and exotic pines in British Columbia. It is described as a new species of Scirrhia Fuckel, and the name S. pini is proposed. The life history, cultural characteristics, and distribution are presented.
A NUMEROTAXONOMIC STUDY OF SOME SPECIES OF TRIFOLIUM, SECTION LUPINASTER
Authors: Parups E. V. , Proctor J. R. , Meredith B. , Gillett J. M.
Published: October 2007

The flavonoid patterns of 11 taxa of Trifolium L., sect. Lupinaster were examined chromatographically. On the basis of the coded data the coefficients of association between the various taxa were determined and a hierarchic system based on chemical evidence established. The methods permitted objective numerotaxonomical use of chromatography to establish and support hierarchic systems and to express the relationships in definite and comparable mathematical terms. T. parryi and T. parryi salictorum were found to be very closely related. T. attenuatum, T. brandegei, and T. haydenii formed the next most related group, while T. kingii, T. dasyphyllum, T. alpinum, T. nanum, T. longipes, and T. latifolium formed a large, somewhat unrelated group of species.
DIFFERENTIATION OF AGROPYRON MOSAIC, WHEAT STREAK MOSAIC, AND A HITHERTO UNRECOGNIZED HORDEUM MOSAIC VIRUS IN CANADA
Authors: Slykhuis J. T. , Bell W.
Published: October 2007

Agropyron mosaic virus (AMV) from Ontario and wheat streak mosaic virus (WSMV) from Alberta readily infected wheat (Triticum aestivum L.) causing mosaic symptoms that could be differentiated only when carefully compared. All isolates of AMV infected Agropyron repens (L.) Beauv. but not oats (Avena sativa L.). WSMV infected oats but not A. repens. Hordeum mosaic virus (HMV) from Alberta caused mottle rather than streak symptoms on wheat, rye, and other common hosts of WSMV, and did not infect A. repens, but, like AMV, it was not transmitted by Aceria tulipae (K.), the vector of WSMV. It infected Hordeum jubatum L., which is not susceptible to AMV or WSMV. It ranked between AMV and WSMV in longevity and tolerance to heat and pH. The particles were flexuous rods similar to those of WSMV, which appear less flexuous and slightly shorter than particles of AMV.The temperatures at which the viruses multiplied and caused symptoms on wheat ranged from 15° to 33 °C for WSMV and 10° to 30° for AMV. HMV multiplied at all temperatures from 10° to 33 °C but caused symptoms only at 10° to 30 °C.Specific antisera were prepared by partially purifying the viruses by differential centrifugation of juice from diseased wheat, emulsifying the juice with adjuvant, then injecting rabbits intramuscularly. The precipitation titers against their homologous viruses were 1/640, 1/1280, and 1/1280 for the WSMV, AMV, and HMV antisera respectively. The WSMV antiserum did not react with the heterologous viruses, but two HMV antisera had a precipitation titer of 1/16 against AMV, and an AMV antiserum had a titer of 1/10 againt WSMV. Cross absorption of each of the antisera with the heterologous viruses did not reduce the titers against the homologous viruses.The infection of wheat with a mild strain of any of the three viruses protected against later infection by a severe strain of the same virus. Both AMV and HMV were synergistic in combination with WSMV. Serological tests demonstrated that both AMV and HMV multiplied in wheat simultaneously inoculated with both viruses, but systemic infection with either virus protected the plants against later infection by the other.Despite general similarities in physical characteristics and effects on wheat, specific differences in other characteristics show that AMV, HMV, and WSMV are sufficiently different to be designated as different viruses rather than closely related strains of one virus.
CHROMOSOME NUMBERS AND TAXONOMY OF SOME CANADIAN ARCTIC PLANTS
Authors: Mosquin Theodore , Hayley Dianne E.
Published: October 2007

Chromosome numbers are reported for 65 species of Canadian arctic plants. The chromosome numbers of Parrya arctica R. Br. (2n = 14 and ca. 21) and of Puccinellia poacea Th. Sor. (2n = 14) are reported for the first time. New numbers are recorded for some species and many species are shown to contain two or more chromosome races. A rationale supporting the counting of chromosomes from populations throughout the ranges of all plant species is given.
Effect of leaf age on photosynthesis and transpiration of cassava (Manihot esculenta)
Authors: Aslam M. , Lowe S. B. , Hunt L. A.
Published: October 2007

The effect of plant and leaf age on CO2-exchange rates (CER) and transpiration rates in 15 genotypes of cassava (Manihot esculenta Crantz) was measured in situ by infrared gas analysis. The plants were grown in a controlled-environment room with a 14-h photoperiod, day–night temperatures of 29–24 °C, and 60–70% relative humidity.Plant age had no effect on leaf CER, whereas transpiration rates in 14-week-old plants were significantly greater than those in 7-week-old plants. Both CER and transpiration rates decreased with leaf age. The decline was negligible when measured at low photosynthetic photon flux density. At saturating light, however, both CER and transpiration rates decreased significantly in most of the genotypes. Significant genotypic differences were observed in the pattern of decline. Both stomatal (rs) and residual (rr) resistances to the diffusion of CO2 increased with leafage in all the genotypes. The relative increase in rr was much greater than the increase in rs. In all the genotypes the ratio rr:rs was greater than unity, suggesting that rr is the major component of the total resistance to photosynthesis. Chlorophyll content and specific leaf weight also varied significantly among the genotypes. However, chlorophyll content decreased and specific leaf weight increased with leaf age.
Prenodule formation and primary nodule development in roots of Comptonia (Myricaceae)
Authors: Callaham Dale , Torrey John G.
Published: October 2007

Seedlings of the sweet fern, Comptonia peregrina (L.) Coult., grown aeroponically, were inoculated with a nodule suspension to allow infection by the actinomycete-like organism which causes nodule formation. Roots with early stages of infection and nodule initiation were fixed, embedded in resin, sectioned, and examined. Infection is infrequent in Comptonia with only a few nodules per seedling root system. Infection via root hair invasion causes the retention of the curled and deformed root hair in an intensely cytoplasmic state with ramification of multiple filamentous strands of the endophyte. A limited cortical proliferation occurs in response to the infection forming the prenodule; endophyte filaments grow radially inward from the base of the infected epidermal root hair and invade a portion of the prenodular cells resulting in their hypertrophy. Distal and proximal to the prenodule site, a number of primary nodule primordia are initiated, varying from a few up to a dozen or more. These primordia appear to develop more or less simultaneously under the stimulus of the invading endophyte; they are like lateral roots in their site of origin, occurring largely opposite the protoxylem poles and involving pericyclic and endodermal cell proliferation. They differ in that the cortical cells external to each primordium are stimulated to undergo divisions and these cortical cell derivatives are incorporated into the developing primordium. The endophyte enters the cortical tissues of the lateral root on which the prenodule has formed and then invades proximal and distal to the infection site, progressing into the cortical tissues of each of the developing nodule primordia. A cork-like layer develops on the original lateral root in areas not occupied by primordia by initiation of subepidermal cell divisions and wall thickening. Normal lateral root primordium formation occurs in the pericycle opposite the protoxylem poles and involves cellular derivatives of the pericycle and endodermis but no cortical cells, which instead are crushed and displaced by the lateral root primordium as it develops. Nodule formation clearly involves complex chemical interactions, which remain for further study, between the host cells and the invading endophyte.
Ultrastructural investigation of various membrane configurations in Nicotiana tabacum
Authors: Gillespie M. C. , Hamilton J. L.
Published: October 2007

Lamellar and tubular inclusion bodies in the cell vacuole became more numerous as the severity of plant stunting was increased. In normal-appearing greenhouse plants, only a few of these inclusions were seen. In vacuoles of the severely stunted plants, much larger quantities of inclusion bodies were observed. In severely stunted plants, lamellar inclusions occurred that contained osmiophilic globules along the lamellar strands. These types of lamellar inclusions were also seen accumulating in the starch cavities of chloroplasts. From these observations, we postulated that a cell, with a given capacity to produce membrane material, produces membranous material in anticipation of growth. When the cell does not grow, owing to stunting, this excess of membrane material forms the large number of inclusion bodies seen in the vacuoles of stunted cells.
A new species of Pestalosphaeria on pine with comments on the generic placement of the anamorph
Authors: Shoemaker R. A. , Simpson J. A.
Published: October 2007

Pestalosphaeria hansenii n.sp. is described fom Pinus caribaea Morelet var. hondurensis Barrett and Golfari needles from Papua New Guinea. Isolations from single ascospores produced a Pestalotiopsis in culture that matched cultures derived from a Pestalotiopsis associated with the teleomorph on the pine needles. The new species is contrasted with Pestalosphaeria concentrica, P. austroamericana, and P. elaeidis. Discussion of the generic placement of the anamorph involves the names Pestalotiopsis, Pestalotia, Truncatella, Monochaetia, Lennisia, Coryneum, Seiridium, and Hyalocera (or Hyaloceras).
Nitrogen assimilation and dissimilation in five genotypes of Brachiaria spp.
Authors: Pereira Pedro Antonio A. , Döbereiner Johanna , Neyra Carlos A.
Published: October 2007

Five genotypes of Brachiaria spp. were planted in a field experiment with and without nitrate fertilization. Nitrogen metabolism was evaluated by measurements of nitrate reductase (NR) activity in leaves, nitrate accumulation in stems, and nitrogenase activity and dentrification in intact soil–plant cores. There were differences between genotypes in all parameters and a tendency was observed for genotypes with high NR activity and nitrate accumulation to have low nitrogenase activity and vice versa. Brachiaria radicans (Tanner grass) was representative for the first type and B. ruziziensis (CPI 30623) for the second. Denitrification reached 7% of the applied N within 63 h and was lowest in Tanner grass and highest in B. brizantha (FL 902-4). Brachiaria ruziziensis (CPI 30623) plants were able to withstand N stress better than B. radicans as a consequence, possibly, of differences in nitrogenase activity.
Vesicular–arbuscular endomycorrhizal associations of some desert plants of Baja California
Authors: Rose Sharon L.
Published: October 2007

Endemic plants of the Sonoran Desert of Baja California were sampled for mycorrhizal associations. Eight of the 10 plant species examined were colonized by vesicular–arbuscular (VA) mycorrhizal fungi. Soil sievings revealed chlamydospores of three VA mycorrhizal Glomus spp.; G. microcarpus, G. fasciculatus, and G. macrocarpus. At the time of sampling, the populations of VA fungal spores in the soil were low, with one to five chlamydospores per 100 g soil sample.
Autoecious species of Puccinia on Cichorieae in North America
Authors: Parmelee J. A. , Savile D. B. O.
Published: October 2007

Seventeen autoecious species of Puccinia occurring on Cichorieae (Asteraceae) in North America were studied. The taxa removed from those usually treated synonymously with P. hieracii include: P. troximontis Pk. and P. hypochaeridis Oud., which are segregated because of their completely echinulate urediniospores. Puccinia agoseridis sp.nov. is also segregated from the same complex because of difference in teliospore wall sculpturing. Both varieties of P. harknessii stand apart from P. hieracii by their more conspicuous teliospore warting. Puccinia harknessii var. harknessii attacks Lygodesmia while P. harknessii var. stephanomeriae comb.nov. occurs on Stephanomeria. Puccinia chondrillina is separated from P. hieracii by its smaller urediniospore tonsures and P. lapsanae possesses tonsures which are absent in P. variabilis. Such morphological differences become more evident with the use of scanning electron microscope examination to support observations with the light microscope.
Differences in the mode of penetration of soybean hypocotyls by two races of Phytophthora megasperma var. sojae
Authors: Stössel P. , Lazarovits G. , Ward E. W. B.
Published: October 2007

Penetration of soybean hypocotyls (Glycine max L. Merr.) cv. Mack following inoculation with zoospores of races 4 (compatible) and 6 (incompatible) of Phytophthora megasperma Drechs. var. sojae Hildeb. was compared with previous observations of penetration of cv. Altona, on which the compatibility of these two races is reversed. On both cultivars race 6 tended to penetrate preferentially between anticlinal walls of adjoining epidermal cells, while race 4 penetrated periclinal and anticlinal walls with almost equal frequency. Thus it appears that the mode of penetration by these two races is not influenced by the compatibility of the interaction but is a characteristic feature of each race.
Cell degeneration and gill remodelling during basidiocarp development in the fungus Coprinus cinereus
Authors: Lu Benjamin C.
Published: October 2007

The early mushroom gill development in a primordium of Coprinus cinereus was studied by electron microscopy. Extensive cell degeneration and cell death were found in gill cavities but not within gill domains. These degenerative cells were found to contain multivesicular and membranous residual bodies, suggesting that the multivesicular bodies are part of the cell degeneration. Cellular debris was observed in intercellular spaces probably as a consequence of cell lysis. The presence of multivesicular bodies was also observed in cells shortly before Coprinus basidiocarps underwent autolysis: a high dose of hydrolytic enzymes can be extracted from such basidiocarps. The high numbers of multivesicular bodies, the membranous residual bodies, and the cellular debris in the primordial tissues are manifestations of cell degeneration that may be a prerequisite to gill remodelling during early primordial development. Key words: cell degeneration, gill remodelling, multivesicular body, residual body, mushroom development.
Cytological studies of the hypersensitive death of cowpea epidermal cells induced by basidiospore-derived infection by the cowpea rust fungus
Authors: Chen C. Y. , Heath Michele C.
Published: October 2007

The cytological responses to the monokaryotic primary hyphae of the cowpea rust fungus (Uromyces vignae Barcl.) were observed in vein epidermal cells of a resistant and a susceptible cowpea cultivar. Unlike the previously examined response to haustoria of a nonpathogenic powdery mildew fungus, plant cell walls did not become autofluorescent in response to fungal penetration, and the primary hypha only rarely became encased. Following fungal penetration, the response of invaded cells of the resistant, intact plant could be divided into the following stages: (I) cytoplasmic streaming normal; (II) cytoplasmic streaming slow or stopped, Brownian motion of particles visible in the vacuole, granulated cytoplasm aggregated along the cell walls, some host nuclei disappeared; and (III) protoplast collapsed. Epidermal tissue of the resistant cultivar did not exhibit stages II–III when detached and mounted in water 12 h after inoculation and examined 9 h later. The frequency of stage III increased when the tissue was mounted in CaCl2, Ca(NO3)2, and KNO3, but only in a kinetin solution did it approximate that in attached tissue. Although kinetin inhibited fungal growth in both the resistant and the susceptible cultivar, the hypersensitive response occurred only in the former, suggesting that kinetin affects the hypersensitive response directly rather than through its inhibitory effect on the fungus. Key words: cowpea, Vigna unguiculata, cowpea rust fungus, Uromyces vignae (Barcl.), hypersensitivity.
Neocallimastix hurleyensis sp.nov., an anaerobic fungus from the ovine rumen
Authors: Webb Jill , Theodorou Michael K.
Published: October 2007

A new member of the Neocallimasticaceae (Spizellomycetales), Neocallimastix hurleyensis sp.nov., is described. This species was isolated from the ovine rumen and has been referred to previously as Neocallimastix sp., strain R1. It has a classical monocentric type of life cycle, with polyflagellated zoospores, endogenous development of the zoosporangium, and death of the thallus following zoospore release. Although N. hurleyensis is similar to two other members of the genus, N. frontalis (the type species) and N. patriciarum, the zoospores possess 8–16 flagella, have no equatorial constriction, and exhibit segregation in the localization of intracellular organelles. A large organelle (presumptive hydrogenosome) is situated in the posterior portion of the cell, in close proximity to the kinetosomal apparatus. It is the size, location, and complexity of this organelle that explicitly distinguishes N. hurleyensis from other members of the genus. Key words: systematics. Neocallimasticaceae, Neocallimastix, Neocallimastix hurleyensis, anaerobic fungi, rumen fungi.
The partitioning of 14C between growth and differentiation within stem-deformed and healthy black spruce seedlings
Authors: Margolis Hank A. , Delaney Sandra , Vézina Louis-P. , Bellefleur Pierre
Published: October 2007

When containerized black spruce seedlings (Picea mariana Mill.) are grown rapidly, their stems can become deformed, i.e., they bend over, grow horizontally, and obtain a permanent crook. To determine what physiological differences exist between these stem-deformed and healthy seedlings, we fed labeled amino acid,14C-phenylalanine, a precursor of lignin and phenolics as well as a constituent of proteins, to both kinds of seedlings and followed the partitioning of this 14C after a chase period of 24, 48, and 72 h. For one group of seedlings, intact plants incorporated the l4C-phenylalanine through their root systems, whereas for a second group of plants, root systems were excised and the 14C-phenylalanine was incorporated directly by stems. When the 14C was incorporated by roots, stem-deformed seedlings partitioned more l4C to protein and less to lignin and phenolics. However, when the 14C was incorporated directly by stems, the differences between stem-deformed and healthy seedlings nearly disappeared. Furthermore, the distribution of 14C following root incorporation in stem-deformed seedlings was the same as that for stem incorporation in both types of seedlings. Thus, stem-deformed black spruce seedlings behave as if their root systems are not performing their normal role in metabolizing phenylalanine into lignin precursors. The ratio of 14C allocated to phenolic-containing compounds associated with growth to 14C allocated to those compounds associated with the differentiation of existing plant structures was 3.7 times higher in stem-deformed seedlings than in healthy ones. These results demonstrate that roots can play an important role in controlling the partitioning of carbon between growth and differentiation. Key words: black spruce, differentiation, lignification, phenolics, stem deformation, secondary metabolism.
New cytotaxonomical determinants recognized in six taxa of Agave in the sections Rigidae and Sisalanae
Authors: Castorena-Sánchez I. , Escobedo R. M. , Quiroz A.
Published: October 2007

New cytotaxonomical determinants are presented for the following taxa of Agave: (I) section Rigidae: Agave fourcroydes Lemaire (5x = 150), first karyotype; Agave angustifolia Haworth (sensu Gentry), new count (6x = 180), first karyotype; Agave angustifolia Haworth var. marginata Hort. (2x = 60); and Agave tequilana Weber, new count (2x = 60), first karyotype; (II) section Sisalanae: Agave sisalana Perrine (5x = 150), first karyotype; and (III) intersectional hybrid: Agave hybrid 11 648 new count (2x = 60), first karyotype. Chromosomes are classified and arm number, chromatin length, and variability are discussed. These results suggest (i) a speciation process via limited rearrangements and point mutations in the small chromosomes of the complement, within the euploidy level rather than karyotype diversification and (ii) a reconsideration to assign them to the 2C level of Stebbins karyotype classification. Key words: fiber agaves, karyotype analysis.
The use of histochemical analysis and stem colonization for distinguishing reactions of alfalfa to verticillium wilt
Authors: Papadopoulos Y. A. , Christie B. R. , Boland G. J. , Busch L. V.
Published: October 2007

The objectives of this study were to investigate resistant responses in cultivated alfalfa (Medicago sativa L.) to verticillium wilt and to develop a selection procedure to distinguish resistant, tolerant, and susceptible genotypes utilizing phenolic compound production. The level of phenolic compound accumulation in infected seedlings was significantly higher than noninfected seedlings. Seedlings of resistant or tolerant entries accumulated higher levels of phenolic compounds than susceptible entries during the first 7 days following inoculation. The results indicate that the levels of phenolic compound accumulation and distribution in the stem vascular region exhibit quantitative differences associated with resistance to Verticillium albo-atrum infection. Furthermore, this chemical response appears to be genetically inherited. The level of stem colonization in resistant entries was slightly lower than tolerant and susceptible entries during the first 2 weeks following inoculation. Susceptible seedlings died during the 8 weeks postinoculation. Six months following inoculation, stem colonization dropped to near zero in the resistant genotypes, whereas it remained high in the tolerant plants. The absence of symptoms is not a reliable indicator of verticillium wilt resistance. Patterns of phenolic compound accumulation and long-term stem colonization can be used as more accurate criteria for distinguishing resistant genotypes from tolerant and susceptible genotypes. Key words: Verticillium albo-atrum, phenols, resistance.
A new Harposporium with triangular conidia attacking bdelloid rotifers
Authors: Barron G. L. , Szijarto E.
Published: October 2007

Harposporium trigonosporum is described as new. After ingestion by rotifers, the traingular conidia lodge any place between the mouth and the anus but most frequently in the lower gut. A filiform germination hypha develops from each corner of the conidium and penetrates through the gut wall into the body cavity of the host. The host frequently responds to this invasion by laying down deposits around the advancing germ tube that sometimes causes the germinating conidium to abort. More frequently a germination hypha breaks through the host deposits at one or more of the three points of attack and proliferates inside the body, resulting in the death of the rotifer. Key words: Harposporium, endoparasite, rotifer.
Nucleolus-associated bodies in meristematic cells of two plant species (Cicer arietinum and Leucaena glauca) with different ploidy levels
Authors: Lafontaine J. G. , Luck B. T. , Gugg S.
Published: October 2007

Light microscopy has shown that plant interphase nuclei contain small, roundish bodies, some of which may be closely associated with the nucleolar surface. Serial sections were used to determine the location, size, and number of these nucleolus-associated bodies in two plant species having different ploidy levels. In Cicer arietinum, a diploid species, one or two such bodies were observed, whereas in Leucaena glauca, an octoploid species, four to six nucleolus-associated bodies were present. At the ultrastructural level, these bodies consistently exhibited a distinct fibrillogranular texture and were located close to segments of the interphase nucleolar organizer track, a meandering, coarse, filamentous structure particularly well developed within many plant species and known to consist partly of chromatin. The fact that the number of these bodies closely matches that of the satellite-bearing metaphase chromosomes suggests that they may represent terminal segments of the nucleolar chromosomes. Other equally plausible interpretations of the nature of the NABs are also considered. Key words: plant interphase nucleus, nucleolus-associated bodies, satellites.
Later events in suppression of Fusarium root rot of red pine seedlings by the ectomycorrhizal fungus Paxillus involutus
Authors: Farquhar M. L. , Peterson R. L.
Published: October 2007

Colonization of primary roots of red pine (Pinus resinosa Ait.) seedlings by two isolates of the fungal pathogen Fusarium oxysporum Schlecht. emend Snyd. & Hans. f.sp. pini in a sterile, soil-free system and a nonsterile rooting medium was suppressed for 2 months if the roots were exposed to the ectomycorrhizal fungus Paxillus involutus (Batsch.) Fr. for 1 week before being inoculated with the pathogen. Roots of protected seedlings harboured only a few hyphae of the pathogen. These were either vacuolated or filled with slightly electron-dense substances and did not penetrate host cells. In contrast, roots of seedlings not inoculated by P. involutus were extensively colonized by F. oxysporum, and host tissue vacuolation and disorganization occurred. Papillae, consisting of either small protuberances or elongate projections, were infrequently formed in response to infection. Chlamydospores of F. oxysporum that formed in the sterile system had numerous lipid deposits and amorphous thick walls but few mitochondria and little endoplasmic reticulum. Key words: biological control, ectomycorrhiza, Fusarium, Pinus resinosa, disease suppression.
Histological localization of psoralens in fruits of Psoralea bituminosa
Authors: Zobel Alicja M. , Brown Stewart A. , March Raymond E.
Published: October 2007

Linear furanocoumarins were found on the surface of Psoralea bituminosa (Leguminosae) fruits in concentrations up to 1% of the total furanocoumarins. Most of the remainder was on the surface of the embryos and very young seedlings, with ca. 4% of the total furanocoumarins within the embryos, and very little in the seed coat and fruit. Psoralen was present in the highest concentration, over twice that of xanthotoxin. There was very little bergapten, whose distribution differed from that of the xanthotoxin and psoralen, ca. 20% being on the surface and the rest in dead tissues, i.e., fruit and seed covers. Evidence was obtained, through autofluorescence, that these coumarins are localized in discrete cells of the embryo, on the embryo surface, and on the fruit surface. Key words: Psoralea, Leguminosae, fruits, furanocoumarins, autofluorescence, histochemistry.
Cell surface interactions between sorghum roots and the parasitic weed Striga hermonthica: cytochemical aspects of cellulose distribution in resistant and susceptible host tissues
Authors: Olivier Alain , Benhamou Nicole , Leroux Gilles D.
Published: October 2007

Cell surface interactions between sorghum roots and the parasitic weed Striga hermonthica were investigated using light and electron microscopy. An exoglucanase–gold complex was used to study the distribution of cellulose in host tissues of resistant and susceptible cultivars. In the susceptible cultivar, intrusive cells of S. hermonthica could reach xylem elements, whereas in the resistant cultivar, development occurred mainly in the outer cortex. Invasion of the susceptible cultivar was accompanied by wall alterations and by the release of cellulose-rich fragments likely detached from host walls through the action of lytic enzymes. The occurrence of wall alterations at a short distance from the point of parasite penetration provided indirect evidence for extracellular diffusion of cellulolytic enzymes. Tylose formation and accumulation of coating material along secondary thickenings of some xylem vessels were late responses observed in the susceptible cultivar. In the resistant cultivar, heavy deposition of successive layers of cellulosic material occurred in outer tissues. Accumulation of this material may constitute a defense reaction against penetration. Electron-dense coating material was noticeable in cortical cells and occasionally in xylem vessels. Defense reactions observed in both sorghum cultivars upon parasite attack differed in their temporal and spatial distribution. Key words: Striga, sorghum, haustorium, root anatomy, gold cytochemistry, cellulose, resistance.
Differences in lichen and bryophyte communities between old-growth and managed second-growth forests in the Swan Valley, Montana
Authors: Lesica Peter , McCune Bruce , Cooper Stephen V. , Hong Won Shic
Published: October 2007

Lichen and bryophyte communities differed between managed second-growth and unmanaged old-growth grand fir forests in northwestern Montana in all three strata examined: lower canopy, trunk, and ground. Old-growth forests had larger trees, greater structural diversity, greater volumes of coarse woody debris, fewer species of vascular plants, more species of trunk epiphytes, higher β diversity, and higher γ diversity than second-growth forests. Although pendent fruticose lichens were common in both stand age classes, species of Alectoria were more abundant in old growth, while second growth was dominated by Bryoria spp. Nitrogen-fixing foliose lichens were more common in all strata of old growth, and Lobaria pulmonaria, a common N-fixing species in old growth, was absent in second growth. Cladonia spp. were more numerous in second-growth forests. Nearly all species of leafy liverworts were more common in old growth and typically occurred on rotting wood. Many of these liverworts were absent from second growth. Our results suggest that many species of lichens and bryophytes find optimum habitat in old-growth forests and that these species will become less common as silvicultural practices continue to convert old growth to younger aged forests. Key words: bryophytes, diversity, forests, lichens, Montana, old growth.
Vegetative compatibility groups and protein electrophoresis indicate a role for basidiospores in spread of Inonotus tomentosus in spruce forests of British Columbia
Authors: Lewis Katherine J. , Hansen Everett M.
Published: October 2007

The importance of spore infection in the spread of Inonotus tomentosus was assessed using vegetative compatibility and protein electrophoresis. Isolates were collected from diseased spruce (Picea glauca × engelmannii) trees from five sites. Each site had several small (two or three trees) discrete disease centres, or larger patchy centres, or both. Within each site, the vegetative compatibility group and protein profiles of isolates were examined in all combinations of paired isolates. Vegetatively compatible isolates had identical protein profiles in 74% of the comparisons. Vegetatively incompatible isolates had different protein profiles 97% of the time. Usually isolates differed by only one or two protein bands. Isolates from a discrete centre were usually vegetatively compatible with identical protein patterns. Larger patchy centres consisted of multiple vegetatively compatible groups. The number of unique vegetatively compatible groups found suggests that spores are an important course of infection. Key words: vegetative compatibility, disease centre, protein electrophoresis.
Assessment of the effect of mycorrhizal fungi on drought tolerance of conifer seedlings
Authors: Boyle C. David , Hellenbrand Klaus E.
Published: October 2007

Methods were evaluated for comparing the potential of mycorrhizal fungi to increase the performance of conifer seedlings during water stress. The ability of five fungi to grow in pure culture under conditions of low water potential was tested. The same fungal isolates were then assessed in association with jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) B.S.P.) seedlings. Mycorrhizal seedlings were subjected to known water stress by exposing their roots to a solution of polyethylene glycol or were planted into systems that allowed the simulation of a drought cycle in a forest soil. The apparent photosynthetic rate or the apparent photosynthetic rate and shoot and root growth were used as measures of seedling performance in the two systems. Fungi that grew well in pure culture under low water potential generally also increased the performance of black spruce. The ability of some fungi to form rhizomorphs extending into the mineral soil layer or to stimulate root growth also correlated with increased performance of black spruce. In contrast, under the experimental conditions used, jack pine showed good performance independent of mycorrhizal status. It is concluded that the screening methods used have value in selecting plant–fungus combinations that have potential to increase performance of conifer seedlings under drought stress. Key words: ectomycorrhizae, conifers, drought, Pinus, Picea.
Carbon and nitrogen partitioning in young nodulated pea (wild type and nitrate reductase-deficient mutant) plants exposed to NO3− or NH4+
Authors: Shelp Barry J. , Taylor David C. , Nelson Louise M.
Published: October 2007

Fresh weight accumulation, and carbon and nitrogen partitioning were investigated in wild type and a nitrate reductase-deficient mutant (A317) of Pisum sativum L. (cv. Juneau), effectively inoculated with Rhizobium leguminosarum strain 128C54. The plants were grown hydroponically in medium without combined N for 21 days, followed by a further 7 days in medium without combined N or with 5 mM NO3− or NH4+. In the absence of combined N, the nitrogenase activity (measured as acetylene reduction and expressed on a specific nodule basis) of A317 was 53% of the wild type. In the presence of combined N the nitrogenase activity of wild-type plants was reduced by 60%, whereas that of A317 was not affected. The decline in the proportion of 14C translocated to nodulated roots that was allocated to nodules only was significant in the wild type. Inorganic N accumulated in the nodule. Nodule concentrations of asparagine and glutamine increased dramatically in both genotypes with NH4+ but not NO3−. The partitioning of sugar and starch was often dependent on the pea genotype and N form. These data suggest that the assimilation of NO3− and (or) NH4+ plays a role in the inhibition of symbiotic N2 fixation by combined N. Key words: carbon and nitrogen partitioning, nitrate reductase, nodulated pea plants.
Type studies in Tylopilus (Boletaceae). V. Taxa described by Alexander H. Smith, Harry D. Thiers, and Samuel J. Mazzer
Authors: Wolfe Jr. C. B.
Published: October 2007

Studies of type specimens of Tylopilus ammiratii, T. humilis, T. felleus var. uliginosus, T. intermedius, T. rubrobrunneus, and T. subfusipes described by Alexander H. Smith, Harry D. Thiers, and Samuel J. Mazzer were conducted. These studies revealed new character data or clarified character data of these taxa. Key words: Boletaceae, Tylopilus, type studies.
Comportement des fractions peroxydasique et catalasique solubles au cours d'interactions entre le piment et le virus de la mosaïque du tabac ou le Phytophthora capsici
Authors: Lizzi Y. , Coulomb Ph. J.
Published: October 2007

Soluble peroxidase (EC 1.11.1.7) and catalase (EC 1.11.1.6) activities were evaluated in leaves of pepper (Capsicum annuum) infected with Phytophthora capsici (causal agent of mildew) and by the tobacco mosaic virus (TMV). Necrotic infections induced large increases in peroxidase activities. However, the extent of the variations was larger in cv. Phyo 636, resistant, than in cv. Yolo Wonder, after contamination with P. capsici. Systemic infection with TMV didn't significantly modify this activity. Infection with P. capsici induced an increased catalase activity, whereas a systemic infection with TMV reduced this activity. Fractions responsible for peroxidase activities were separated by electrofocusing on agarose gel. Necrotic fungal or viral interactions strongly affected the activity of the anodic and neutral fractions of total soluble extracts. A race–cultivar response was observed during the interactions with P. capsici. One of the fractions was strongly inducible. Studies conducted in the perinecrotic areas, following infection by P. capsici, showed inversely proportional gradients in peroxidase and catalase activities. Contamination with P. capsici stimulated soluble peroxidase activities located in the intercellular compartment where all fractions were represented. One of the fractions was strongly stimulated. On the opposite, catalase activity was reduced in this compartment. Differences observed in the activity patterns of the isoperoxidases suggest a specific role for each of them. Data on intra- and extra-cellular compartments suggest the existence of a selective molecular movement. The activity pattern of catalase and of peroxidase indicate a regulation of hydrogene peroxyde rate acting, at low concentrations, as a secondary messenger and contributing, at high concentrations, to the destruction of pathogenic organisms in the intercellular spaces. Key words: Capsicum, Phytophthora, tobacco mosaic virus (TMV), electrofocusing, peroxidase, catalase.
The postfire recovery of rock-inhabiting algae, microfungi, and lichens
Authors: Garty Jacob
Published: October 2007

Despite numerous investigations on the re-establishment of epiphytic cryptogams, especially lichens, after forest fires, very little is known about the recolonization of burnt rocks by lithobiontic microorganisms after fire in the Mediterranean region. Reported herein are the results of a combined field observation and scanning electron microscopy study focusing on the connection between the microrelief of the rocks that was shaped during prefire periods and the recolonization of pioneer lithobiontic microorganisms after the fire. Scanning electron microscopy revealed that the burnt rock surfaces exhibit 10 kinds of weathering elements that include 9 kinds of cryptogamic imprints corroded by saxicolous (rock-inhabiting) unicellular green algae, free-living microfungi, and fruiting bodies or microgrooves of endolithic lichens during prefire periods. The total volume of several selected structural weathering elements formed by lithobiontic microorganisms during the prefire period was estimated relative to the possible contribution of these lithobionts to local pedogenesis. Considering that the specific weight of chalk is 2.6 g/cm3, the estimated amount of the rock material removed by small pits with a diameter of 0.01 mm formed by unicellular green algae during the prefire period can reach 3.06 kg/ha mountain area with 10% rock coverage, while the estimated amount of chalk rock material removed by pinhead holes with a diameter of 0.8 mm formed by fruiting bodies of endolithic lichens can reach 174 kg/ha with the same rock coverage. Water-holding capacity of empty pinhead holes and small pits on the rock surface in burnt areas was also estimated, and it is suggested that the water-holding capacity of empty small pits (d = 0.01 mm) formed by unicellular green algae on rock surface per hectare mountain area with 10% rock coverage can reach 1.18 L, whereas in case of pinhead holes (d = 0.8 mm) formed by fruiting bodies of endolithic lichens the water-holding capacity can reach 66.9 L/ha with the same rock coverage. Scanning electron microscopy revealed the presence of three different kinds of unicellular green algae, one free-living microfungus, two different species of endolithic lichens, two epilithic lichen species, and great numbers of lichen ascospores, fungal spores, and hyphae established postfire in pinhead holes and small pits produced by former microlithobionts inhabiting rocks during prefire periods. These microorganisms and diaspores were also present in ruts, shallow rock depressions, and microcrevices produced by abiotic factors. Key words: lithobiontic microorganisms, wildfire, algae, microfungi, lichens.
Effect of water depth on population parameters of a Typha glauca stand
Authors: Waters I. , Shay J. M.
Published: October 2007

The response of a Typha glauca stand to a water depth gradient was studied in a small marsh pond in Delta Marsh, Manitoba. Weekly density counts and height measurements were made from May to October 1986 in permanent quadrats at five depths from 25 to 100 cm. Shoot mass was estimated from shoot height using a regression model based on destructive analyses. Shoot density declined significantly from 41 shoots/m2 at 25 cm to 12 shoots/m2 at 85 cm but increased at 100 cm to 38 shoots/m2. Shoot mass increased in shoots growing at water depths from 25 to 65 cm, resulting in relatively constant stand biomass over this depth range. Stand biomass declined at 85 cm and reached its maximum (1789.8 g/m2) at 100 cm. Frequency distributions of shoot size categories based on height deviated from normality and were negatively skewed at all depths, with the greatest skewness occurring at 100 cm. These population parameters were interpreted as evidence of a plastic population response to water depth. Key words: clonal macrophyte, frequency distributions, plasticity, shoot density, Typha glauca, water depth.
Effect of sexual recombination in two populations of the wheat leaf rust fungus Puccinia recondita
Authors: Kolmer James A.
Published: October 2007

The effect of sexual recombination on diversity and distribution of virulences was measured in two random mating populations of Puccinia recondita f.sp. tritici from the eastern and prairie regions of Canada. Teliospores derived from composite uredinial collections from both populations were germinated over leaves of Thalictrum speciosissimum, and aeciospore isolates were derived from fertilized pycnia. Virulence phenotypes of aeciospore isolates in both populations were determined on isogenic host differential sets. Comparisons of phenotypic diversity, distribution of specific virulences, and differences in specific virulences among phenotypes were made between the progenitor uredinial populations and the derived aecial populations. Sexual recombination had a greater effect of increasing diversity and randomly distributing virulences in the eastern aecial population than in the prairie aecial population. The differences in the two aecial populations most likely resulted from linkage disequilibrium between virulences generated by host selection in the prairie uredinial population, compared with the lower initial level of disequilibrium in the relatively unselected eastern uredinial population. Key words: phenotypic diversity, linkage disequilibrium, specific virulence.
Phenology and seed production in Chenopodium rubrum, Rumex maritimus, and Rumex palustris as related to photoperiod in river forelands
Authors: Sman A. J. M. Van der , Blom C. W. P. M. , Steeg H. M. Van de
Published: October 2007

Reproductive development in three species from irregularly flooded areas of river forelands was studied in relation to time of emergence. In Chenopodium rubrum, flowering was induced earlier in plants germinated in April–May than in later cohorts. However, the period of vegetative growth diminished and the life cycle was completed in a shorter time in later germinated plants. Seed number was reduced, but seed size as well as reproductive effort per plant increased in later cohorts. Plants of both Rumex species flowered after a certain number of leaves had developed and before a critical photoperiod had passed. In earlier cohorts, the main shoot and several axillary shoots elongated and flowered. Fewer axillary shoots flowered closer to the critical photoperiod, and this resulted in a reduced seed output in later cohorts. The critical photoperiod as well as the time needed for completion of the life cycle was longer in Rumex palustris than in Rumex maritimus. It is argued that in the riparian habitat, plants of both Rumex species are only occasionally able to complete their life cycle in one growing season. Survival of these species on the population level will rely more upon adaptations towards flooding during the established phase than is the case for C. rubrum. Key words: flowering phenology, photoperiod, seed production, Chenopodium rubrum, Rumex maritimus, Rumex palustris.