bluuebunny/crossref_metadata_2025 huggingface dataset:
Hierarchical structure of pathogenic variation among Rhynchosporium secalis populations in Idaho and Oregon
Authors: Goodwin Stephen B. , Allard Robert W. , Hardy Shirlee A. , Webster Robert K.
Published: April 2011

Ninety-four isolates of Rhynchosporium secalis, the causal organism of the barley scald disease, from four populations (infected fields) in Idaho and eight in Oregon, were tested for pathogenicity to 14 barley differential cultivars; 60 distinct pathotypes, 33 in Idaho and 28 in Oregon, were found among the 94 isolates. Pathogenicity to most of the differentials was found in each local population sampled. One differential cultivar, CI 5831, was resistant to all isolates tested. Isolates from the same cultivar in different locations usually had different pathogenicities, and most pathotypes were genetically heterogeneous mixtures of many different genotypes based on previous electrophoretic data. The sampled cultivars generally had few or no resistance genes, suggesting that the R. secalis populations in Idaho and Oregon are characterized by large amounts of seemingly unnecessary pathogenicity. When the total pathogenic diversity was partitioned into hierarchical components using the Shannon information statistic, 58% was accounted for by the within-population component, 33% among populations within regions, and only 9% by the between-region component. Because most of the pathogenic variation is within local populations, these populations should adapt rapidly to introduced resistance genes; therefore traditional methods of breeding for resistance to R. secalis using single major resistance genes are not likely to be effective in the Pacific Northwest. Key words: pathogenicity index.
Nutrient availability in Corsican pine stands in The Netherlands and the occurrence of Sphaeropsis sapinea: a field study
Authors: Dijk H. F. G. Van , Gaag M. Van der , Perik P. J. M. , Roelofs J. G. M.
Published: April 2011

To investigate whether there is a relation between the availability of nitrogen and the incidence of damage caused by the parasitic fungus Sphaeropsis sapinea (Fr.) Dyko & Sutton in Corsican pine (Pinus nigra ssp. laricio (Poir.) Maire) stands, needle and soil samples were taken in 29 stands in spring and early summer of 1986. The infected stands proved to contain higher nitrogen levels in the needle tissue and concomitant higher ammonium levels in the soil. Phosphorus was also present in larger amounts in needle tissue and soil. Most of the additional nitrogen in the needles of the affected stands was stored in free amino acids. Particularly the levels of the nitrogen-rich amino acids asparagine, glutamine, histidine, lysine, and arginine strongly increased. Arginine was by far the most abundant free amino acid in both healthy and infected stands. Also proline showed a remarkable rise in concentration. These results are discussed with regard to other recent Dutch field and greenhouse studies concerning S. sapinea. Key words: Sphaeropsis sapinea, Pinus nigra ssp. laricio, nitrogen.
Acid phosphatase activity in Pinus pinea – Tuber albidum ectomycorrhizal association
Authors: Pasqualini S. , Panara F. , Antonielli M.
Published: April 2011

Acid phosphatase activity of pine (Pinus pinea L.) roots was investigated in the presence or absence of the ectomycorrhizal fungus Tuber albidum Pico. Acid phosphatase activity was higher in mycorrhizal roots than in roots of uncolonized control plants. The optimum pH values for acid phosphatase were 3.5 and 5.0 for mycorrhizal roots and 5.0 for control roots. The acid phosphatase activity was inhibited by tartrate, fluoride, and molybdate ions, but a lower inhibition was exerted by orthophosphate. Mycorrhizal roots of pine possessed active acid phosphatases that hydrolyzed a wide variety of natural and synthetic phosphate esters. In particular, the enzyme was active against phytate and inorganic pyrophosphate. Two different Km values were estimated: about 0.22 mM and 2.78 mM at low and high substrate concentrations, respectively. The ultrastructural localization of acid phosphatase in mycorrhizal roots showed that the activity in the Hartig net was mainly localized in the plasmalemma of hyphae. Some lead phosphate precipitates were also observed in the middle lamella of the host cell. Key words: Pinus pinea, Tuber albidum, acid phosphatase, ectomycorrhiza, histochemical localization.
Measurement of the pulling force of a single contractile root
Authors: Pütz Norbert
Published: April 2011

A technique is described that can be used for direct measurement of the force of a single contractile root. This lifting technique has been tested on five species. It is shown that the results from direct measurement are in general agreement with those obtained with an indirect measurement. This new technique makes it possible to measure the pulling force of plants with specialized movements, e.g., Triteleia hyacinthina, in which contractile roots produce a channel for the movement of the offset. Although Triteleia contractile roots have what has been described as a 100% channel effect, measurements with the lifting technique show that a pulling force can, indeed, be measured. Key words: contractile root(s), monocotyledons, root contraction, plant movement, Triteleia hyacinthina, Sauromatum guttatum.
Ultrastructure and development of the outer epidermal wall of spruce (Picea abies) needles
Authors: Tenberge Klaus B.
Published: April 2011

The outer epidermal wall of Picea abies needles was investigated throughout its life-span. Several cytochemical procedures at the light and electron microscope level including enzyme–gold affinity labeling and elemental mapping by electron energy loss spectroscopy were applied to gain detailed information about its fine structure. The adult outer epidermal wall averages 9 μm in thickness and occupies half the cell height. It is composed of five main layers and additional epicuticular waxes. In the cuticular membrane a thin homogeneous cuticle proper is clearly distinguishable from the cuticular layer, which is composed of an exterior striated, a middle reticulate, and an interior arborescent sublayer. Cellulose and mannans were localized and identified among other polysaccharides in the cuticular layer in situ. Arborescent structures extend to an adjacent, usually lignified layer, containing numerous calcium crystals. Beneath this is an electron-dense layer, formed mainly of hemicelluloses. The innermost wall layer comprises several alternately arranged lamellae formed of several types of polysaccharides and differing mainly in their polyphenol content. During ontogeny of the outer epidermal wall, lasting a whole year, five phases were distinguished: a protodermal phase, one of even growth, one of uneven growth, and one of lignification and further growth. With the fifth phase the outer epidermal wall of current needles achieves maturity in late autumn. No differences in ultrastructure and development of the outer epidermal wall between apparently healthy and damaged needles were observed. Key words: Picea abies, outer epidermal wall, light and electron microscopical cytochemistry, enzyme–gold technique, polysaccharides, calcium crystals.
Biosorption of metal ions by Armillaria rhizomorphs
Authors: Rizzo D. M. , Blanchette R. A. , Palmer M. A.
Published: April 2011

Armillaria rhizomorphs consist of differentiated hyphae with a melanized outer cortex. Melanin is known to prevent lysis of fungal structures by hydrolytic enzymes and may protect against antagonistic microorganisms. Our studies indicate that melanized rhizomorphs also adsorb high concentrations of cations from the surrounding soil environment. Rhizomorphs of four Armillaria species (A. ostoyae (Romagn.) Herink, A. calvescens Bérubé & Dessureault, A. gemina Bérubé & Dessureault, and A. sinapina Bérubé & Dessureault) collected from Minnesota, New Hampshire, and Oregon had substantially elevated levels of metal ions compared with the soil from which they were collected. With some elements, ions were 50–100 times more concentrated on rhizomorphs than in soil. Concentrations of Al, Zn, Fe, Cu, and Pb on rhizomorphs ranged up to 3440, 1930, 1890, 15, and 680 μg/g, respectively. Energy dispersive X-ray microanalysis showed that metal ions were located only on the outer portions of the rhizomorphs and not concentrated in the interior. A coating of metal ions may play a key role in the longevity and survival of rhizomorphs in soil. Key words: Armillaria, rhizomorphs, metals, fungal antagonism.
N2 fixation in a young Alnus incana stand, based on seasonal and diurnal variation in whole plant nitrogenase activity
Authors: Huss-Danell Kerstin , Lundquist Per-Olof , Ohlsson Helene
Published: April 2011

N2 fixation by grey alder, Alnus incana (L.) Moench, was studied in the field during two growing seasons in northern Sweden. Alders were planted in a nitrogen-poor soil. Each alder had its root system enclosed in an open-ended cylinder that was closed with a gas-tight lid around the stem base to serve as cuvette during nitrogenase activity (acetylene reducing activity) measurements. To follow the seasonal variation, nitrogenase activity was measured at noon on 15 occasions for each alder in 1987 and on 15 occasions in 1988. Diurnal variation in nitrogenase activity was studied at six occasions, but no obvious pattern in the diurnal variation was found. Nitrogenase activity began shortly after leaf emergence at the very end of May, increased in June, stayed high although with some variation through July and August, declined during September, and was zero in early October. Cumulative nitrogenase activity over the season was converted to cumulative N2 fixation after determination of molar ratio nitrogenase activity to N2 fixation. This conversion was facilitated as the Frankia chosen as symbiont was lacking hydrogenase activity. Control experiments showed that the introduced symbiont was the only infective Frankia in the soil. N2 fixation was estimated to be 0.23 and 2.83 g N/(alder∙year) in the 1st and 2nd year, respectively. Despite its young age, A. incana was apparently capable of high N2 fixation rates at the high latitude studied. Key words: Alnus incana, hydrogenase, intact plants, N2 fixation, seasonal variation, spreading of Frankia.
The effect of abscisic acid and abscisic acid metabolites on the germination of cress seed
Authors: Gusta L. V. , Ewan B. , Reaney M. J. T. , Abrams S. R.
Published: April 2011

Optical isomers of abscisic acid (ABA) and racemic mixtures of both abscisic acid and abscisic acid metabolites were studied to determine their effects on the emergence of root primordia and cotyledons from cress seed. The relative emergence sensitivity of cress seed to the racemic compounds was (±)-ABA aldehyde ≥ (±)-ABA alcohol > (±)-ABA > (±)7′-hydroxy ABA > (±)-phaseic acid. Thus ABA and ABA precursors were effective inhibitors whereas the ABA catabolites, phaseic acid, and 7′-hydroxy ABA had little or no effect on germination. The naturally occurring optically pure enantiomer (+)ABA was a more potent germination inhibitor than synthetic (−)-ABA. An ABA analog, 2′,3′-cis dihydro ABA (DHABA), that is not metabolized to phaseic acid was also studied for inhibitory activity. Although optically pure DHABA has the same configuration at C-1 as (+)-ABA, it was less inhibitory than (+)-ABA and its (−) enantiomer was inactive. The pattern of activity observed in treatments with the enantiomers of DHABA indicates that the configuration at C-1′ is important for maximum inhibition of cress seed germination. It also suggests that in contrast to monocot seeds, the formation of phaseic acid is not required for the inhibition of cress seed germination. Key words: abscisic acid, phaseic acid, ABA alcohol, ABA aldehyde, 7′OHABA, germination, ABA analogs.
Déterminisme de la reproduction sexuée du Phaeosphaeria (Leptosphaeria) nodorum agent de la septoriose du blé. II. Action de la température et de la lumière
Authors: Halama P. , Lacoste L.
Published: April 2011

Perithecial formation of Phaeosphaeria nodorum is obtained in vitro on sterilized wheat straws, under strict conditions of light and temperature. The absence of any reproductive form in the dark indicates photoinduction. The different parameters of light (duration, quality, and intensity) influence perithecial morphogenesis. A 12-h photoperiod, near ultraviolet light (300 nm < λ < 400 nm), and intensities of 400 and 600 μW/cm2 are the most favourable conditions for perithecial differentiation. The perithecial production occurs best at 10 °C, is markedly reduced at 14 °C, and absent above 14 °C. Light and temperature have a sequential influence on the successive stages of perithecial development. Whereas primordial formation is photoinhibited and cryostimulated, transformation to the early stage of perithecial development is photoinduced and not affected by temperatures of 10 and 18 °C. The subsequent stages up to ascogenesis are photostimulated and cryoinduced, and ascosporogenesis is photoindependent and cryostimulated. Key words: Phaeosphaeria, Leptosphaeria nodorum, perithecia, light, temperature.
Territorial distribution of histone H1 alleles in a population of Vicia unijuga formed after urbanization of natural habitat
Authors: Berdnikov V. A. , Bogdanova V. S. , Rozov S. M. , Gorel F. L.
Published: April 2011

Territorial distribution of four alleles of one histone H1 subtype was investigated in the natural population of a leguminous plant Vicia unijuga A.Br, inhabiting an area of about 35 km2, including Novosibirsk Academy Town (Akademgorodok). Histone H1 was isolated from pools of 100 plants (one leaflet per plant) collected from points of approximately 100 m2. The proportion of alleles estimated for 119 different points revealed a radial cline. The frequency of an allele that predominates everywhere in the circumference decreases towards the historical centre of Akademgorodok, while two other alleles show the opposite tendency. The observed pattern of territorial distribution was likely due to some man-caused factor (presumably insecticide treatment) that has been acting for a period of time not exceeding the 25 years of Akademgorodok's existence. Key words: histone H1 polymorphism, Vicia unijuga A.Br., natural selection in an urbanized area.
Estimating the composition of a forest seed bank: a comparison of the seed extraction and seedling emergence methods
Authors: Brown Doug
Published: April 2011

The composition of a forest seed bank was estimated using two methods: (i) seed extraction, i.e., the physical separation of the seeds from the soil via flotation in a salt solution, and (ii) seedling emergence, i.e., the germination of seedlings from soil samples incubated under greenhouse conditions for 5 months. The extraction method predicted a density of 12 500 seeds∙m−2, while the emergence method detected 3800 émergents∙m−2. There was considerable disparity in species composition derived from the two methods. The extraction method identified 102 different taxa, with 22 species making up 99% of the seeds and 5.6 + 0.2 species per sample. In contrast, the emergence technique identified fewer species (60) but had more species per sample (7.6 + 0.2). Eleven species made up 99% of the emergents. Verbascum thapsus represented 34% of the seedlings in the emergence study but only 1 % of the extracted seeds. Members of the Polygonaceae represented 19% of the extracted seeds but less than 1 % of the seedling emergents. No tree or shrub species were found with the emergence method, although they represented 8% of the extracted seeds. There was a poor correlation between the estimates of species number, seed density, and diversity obtained from the two methods. The seed extraction method had considerably higher variability for these parameters. It is apparent from this study that the seedling emergence and seed extraction methodologies do not produce similar estimates of the seed bank composition. The differences are such that comparisons should not be drawn between studies using the different methods. Careful considerations should be given to both the objectives of the seed bank study and the relevant literature prior to the selection of an appropriate method. Key words: seed bank, method, composition, diversity, density, sample number.
Systematics of economically important marine algae: a Canadian perspective
Authors: Bird C. J. , Meer J. P. van der
Published: April 2011

Marine algae of economic importance encompass species of positive value, such as seaweeds harvested for food or hydrocolloid extractives, and species with negative effect, such as toxic phytoplankton or nuisance macrophytes. Only a small part of the global algal resource is obtained in Canada, and the overall benefit to the nation's economy is relatively minor, but there exists the potential for further development of useful species. On the other hand, the negative effects of toxic microalgae are increasing, in the form of losses to the shellfish fishery and aquaculture industry and the cost of providing toxicity-testing and phytoplankton-monitoring services. It is obvious that effective utilization of valuable algae, or defense against undesirable ones, must be attended by sound taxonomy to ensure that algae of interest are correctly identified and recognizable. However, the algae present particular problems to systematists, a major one being the variety of life histories, which may involve independent and conspicuous dissimilar phases. In addition, many algae are phenotypically highly variable in response to environment, which is often insufficiently appreciated. The converse situation also exists, in that morphologically similar species are sometimes regarded as a single entity. Algal taxonomists should strive to determine which variations are genetic and therefore taxonomically significant. To illustrate these points, we review recent taxonomic studies on some algal genera of present or potential economic importance in Canada. Key words: marine algae, systematics, economic potential, variability, genetics.
Pectin degradation during root decay of rubber trees by Rigidoporus lignosus
Authors: Nicole Michel R. , Benhamou Nicole
Published: April 2011

Aplysia gonad lectin, which binds polygalacturonic acid, was complexed to colloidal gold and used for localizing molecules that contain polygalacturonic acid in rubber tree roots infected with the white-rot root fungus Rigidoporus lignosus. Colonization of root tissues was associated with strong wall alteration of phloem cells and with degradation of the compound middle lamella in both the phloem (10 weeks after inoculation) and the xylem (15 weeks after inoculation). Our data suggest that pectin breakdown during root decay likely occurs after cellulose and lignin breakdown and may result from the fungal pectinase activities that were detected in vitro. Released pectin oligomers may act as inducers of both fungal laccase and of the tree defense system during root invasion. Key words: root rotting fungi, rubber, pectin, cellulose, cytochemistry.
Seed bank composition in a subarctic pine–birch forest in Finnish Lapland: natural variation and the effect of simulated acid rain
Authors: Vieno M. , Komulainen M. , Neuvonen S.
Published: April 2011

The seed bank composition and seedling densities were determined for a subarctic pine–birch forest. Samples (12 × 12 cm) were taken from plots that had received sulphuric acid and (or) nitric acid irrigation of pH 3 for 5 years and from irrigated control plots. The average seedling density per plot calculated from seedbank samples was 912/m2, varying from 191 to 5240. All the main aboveground taxa were present in the emerging seedlings with Betula sp. and Empetrum nigrum ssp. hermaphroditum being dominant. Other common seed-bank species included Vaccinium uliginosum, Vaccinium vitis-idaea, and Festuca ovina. Acid treatment did not have any significant impact on the composition of the seed bank or on germinative capacity in general. These findings indicate the existence of a viable soil seed bank in northern subarctic forests and the persistence of viability in spite of moderate acid deposition. Key words: seed bank, simulated acid rain, subarctic forest, seedling.
An ultrastructural study of cell division in the coralline red alga Bossiella orbigniana
Authors: Broadwater Sharon , Scott Joe , Field Dawn , Saunders Bill , Thomas Jewel
Published: April 2011

This investigation of Bossiella orbigniana (Decaisne) Silva ssp. orbigniana represents the first ultrastructural account of cell division in the order Corallinales. The mitotic process in this alga is differentiated from that of other red algae by a combination of characters. During prometaphase–metaphase the division poles contain unusual membrane arrangements including quantities of smooth-surfaced membranes and elongate extensions of perinuclear rough ER. At anaphase extensive remnants of nucleolar material attach to the chromosomes, trailing them to the poles. After telophase, the distal nucleus continues to move toward the apex resulting in much greater nuclear segregation than accomplished by anaphase alone. Cytokinesis is temporally displaced from mitosis and displaced distally from the metaphase plate. A reevaluation of ultrastructural patterns of red algal cell division suggests that there are two basic types of mitosis, the polar gap type and the polar fenestrations type to which B. orbigniana belongs. These two types are differentiated by a number of characters with the most important being the configuration of the prometaphase–metaphase polar region and spindle origin. Key words: Bossiella, cell division, Corallinales, mitosis, phylogeny, red algae.
Seed and vegetation dynamics in an alpine herb field: effects of disturbance type
Authors: Chambers Jeanne C.
Published: April 2011

Relationships among the aboveground vegetation, seed rain, and seed bank were examined on a late seral herb field characterized by pocket gopher disturbance and on an early seral gravel borrow that had been severely disturbed 35 years ago on the Beartooth Plateau, Montana. Aboveground vegetation cover was assessed by species in twelve 5-m2 plots. Seed rain was sampled during the 1988, 1989, and 1990 growing seasons with pitfall traps, and the soil seed bank was sampled in fall 1989, spring 1990, and fall 1990. The seed rain (filled seeds) on the borrow area ranged from 7730 to 14 009 seeds/m2 and was higher than that found on other alpine sites; that on the Geum turf ranged from 3375 to 6179 seeds/m2 and was similar to that for other alpine sites. Although highly variable among dates on the borrow area, the seed banks were similar to those of comparable alpine sites. Seed bank density ranged from 1980 to 6003 seeds/m2 on the borrow area and from 3202 to 4647 seeds/m2 on the Geum turf area. The Geum turf area had higher vegetation cover than the borrow area (87 vs. 25%) and higher numbers of species in the aboveground vegetation, seed rain, and seed bank. Relationships among the aboveground vegetation, seed rain, and seed bank were largely determined by the disturbance characteristics of the different sites and the life-history strategies of the dominant species. Medium-lived species, primarily grasses, with high production of small and compact seeds had colonized the borrow area. Despite establishment of other species, 35 years after disturbance the medium-lived species still dominated the aboveground vegetation, seed rain, and seed bank. Species abundances in the three different components were all highly correlated. In contrast, on the Geum turf area there were no correlations among the aboveground vegetation, seed rain, or seed bank. Long-lived forbs that produced low numbers of relatively large seeds dominated the aboveground vegetation and persisted on the area primarily in the vegetative state. The same medium-lived species that dominated the borrow area had the highest abundance in the seed rain on the Geum turf area and appeared to persist by colonizing small-scale disturbances caused by gopher burrowing. Short-lived species with small, long-lived seeds existed on the site primarily through a highly persistent seed bank. The relationships among the aboveground vegetation, seed rain, and seed bank on the Geum turf and borrow areas are compared with those observed for more temperate systems following disturbance. Key words: alpine, herb field, Geum turf, disturbance, vegetation cover, seed rain, seed bank, colonization, establishment, succession.
Influence of ionic composition of the culture medium on de novo flower formation in tobacco thin cell layers
Authors: Cousson Alain , Van Kiem Tran Thanh
Published: April 2011

Floral and vegetative organogenesis in thin cell layers of Nicotiana tabacum cv. Samsun was studied in relation to the ionic composition of the medium. The control liquid medium was buffered to pH 5.5. NH4+, NO3−, K+, and Ca2+ were separately varied between 0 or 0.1 times and 2, 3 or 4 times their initial control concentration. Increasing the concentrations of NO3−, and Ca2+ above their control concentration promoted the formation of vegetative buds instead of flowers. When K+ at 80.0 mM, Na+ at 78.9 mM, and NH4+ as the sole nitrogen source used, neither flower formation nor morphogenesis were observed in 70, 100, and 100% of the explants, respectively. NH4+ as the sole nitrogen source acidified the medium to pH 4.2, whereas the other ionic conditions did not change the external pH. NO3− at 7.9 mM prevented this acidification and allowed flower formation in 75% of the explants. This acidification could increase the K+ and Na+ influxes via a possible lowering of the intracellular pH. This hypothesis corroborates the morphogenic effect of K+ and Na+. Key words: absence of morphogenesis, acidification of medium, floral and vegetative organogenesis, ionic composition of the medium, thin cell layers, Nicotiana tabacum cv. Samsun.
Mycorrhizal dependence of modern wheat cultivars and ancestors: a synthesis
Authors: Hetrick B. A. D. , Wilson G. W. T. , Cox T. S.
Published: April 2011

To supplement previous studies, wheat ancestors with the A, S(B), D, and AB genomes and modern spring and winter wheat cultivars were vernalized for 42 days in a growth chamber prior to transplanting and growth in a greenhouse for 14 weeks. One-half of the seedlings were inoculated with a mixture of equal numbers of spores of six vesicular–arbuscular mycorrhizal fungi at transplanting. Dry weights of plants and component parts were determined. Percent colonization of roots was determined microscopically. Growth response and mycorrhizal dependence were calculated. However, no mycorrhizal dependence was observed in Triticum monococcum PI 266844 and PI 355520 (A genome), Aegilops speltoides 1773 (S(B) genome), or in the AB genome ancestors Triticum carthlicum 2825, Triticum polonicum 2808, Triticum dicoccum 1165, Triticum pyramidale 2809, Triticum orientale 2805, Triticum paleocolchicum 2807, and Triticum persidum 2811 and 2812. Mycorrhizal dependence in the D genome ancestors was more variable. Triticum tauschii var. typica accessions 1649, 1691, 2378, 2448, 2492, 2495, 2528, 2541, and 2567 lacked dependence, whereas T. tauschii var. meyeri 2529 and var. strangulata 2377 and 2452 were dependent on mycorrhizal symbiosis. The spring wheat cultivars Chinese Spring 3008, Spelta 2603, Pavon 76 2980, and Norin 29 3025 and the winter wheat cultivars TAM 200, Wrangler, Saluda, and Karl were not dependent on mycorrhizae, whereas winter wheat cultivars TAM 107 and Century were dependent. When these data are synthesized with previously tested ancestors, landraces, and cultivars, it appears that both dependent and nondependent diploid ancestors with the A, S(B), and D genomes existed, but dependence was lost in tetraploid ancestors. Since no dependence on mycorrhizae has been demonstrated in any AB genome ancestors, the presence of dependence in modern cultivars of the hexaploid ABD genome is probably derived from the D genome. The consistent dependence of wheat cultivars released before 1950 suggests that modern breeding practices have reduced dependence on mycorrhizal symbiosis. The implications of having mycorrhizal colonization in the absence of mycorrhizal dependence (benefit) are discussed. Key words: pathogenesis, growth response, vesicular – arbuscular mycorrhizae.
Involvement of auxin in the loss of apical dominance and plant growth potential accompanying aging of potato seed tubers
Authors: Kumar G. N. M. , Knowles N. Richard
Published: April 2011

Studies were conducted to further characterize a role for auxin in the loss of apical dominance and plant growth potential that occurs during long-term storage of potato (Solanum tuberosum L.) seed tubers. Treatment of single-eye seed cores from 18-month-old seed tubers with 1-naphthaleneacetic acid (NAA) restored apical dominance and increased dry matter partitioning to roots, stems, and leaves, thus partially mitigating the deleterious effects of advanced seed-tuber age on growth potential. Conversely, NAA treatment of seed cores from 6-month-old tubers substantially inhibited plant growth. In contrast to NAA, IAA was totally ineffective at counteracting the deleterious effects of advanced tuber age on plant growth, whereas the effect of IAA on overall growth of plants from 6-month-old seed cores remained slightly inhibitory. The difference in efficacy of these two auxins appears to be related to age-induced differences in ability of tissues to transport and catabolize IAA. The specific activity of IAA oxidase (IAAox) was 4 times higher in tissue from 20-month-old seed tubers at planting and increased at a faster rate during sprouting compared with that from 8-month-old tubers. Hence, the higher potential for oxidation of IAA in tissue from older seed cores is well correlated with the inability of this auxin to alter growth. In translocation studies, etiolated sprouts from aged seed tubers showed a reduced ability to translocate [1-14C]IAA basipetally compared with those from younger tubers. Moreover, intact etiolated sprouts growing from older seed cores decarboxylated the radiolabeled IAA at a much faster rate on a dry weight basis than those from younger seed cores. The specific activities of IAAox and peroxidase in the sprout apex, sprout base, and tuber tissue from 18-month-old seed cores were substantially higher than in similar tissues from 6-month-old seed cores, and tissue concentration of the radiolabel was negatively correlated with IAAox activity. Hence, aging of potato seed tubers not only reduces the ability of sprouts to transport auxin basipetally, but it also increases the capacity for auxin catabolism during sprouting. The physiological consequence of this may be the release of lateral meristems from correlative inhibition, and in effect, reduced apical dominance and shoot growth potential during plant establishment from aged seed tubers. Key words: potato, age-reduced vigor, sprouting, apical dominance, auxin.
Differentiation of intersterility groups and geographic provenances among isolates of Heterobasidion annosum detected by random amplified polymorphic DNA assays
Authors: Garbelotto Matteo , Bruns Thomas D. , Cobb Fields W. , Otrosina William J.
Published: April 2011

Random amplified polymorphic DNAs were correlated with the intersterility group and the geographic provenance of 36 isolates of Heterobasidion annosum from North America and Europe and of one herbarium collection of basidiocarps from California. This technique is very precise and yields higher resolution than previous studies implementing techniques such as isozyme electrophoresis and restriction fragment length polymorphisms. Random amplified polymorphic DNAs revealed differentiation among the following geographic groups and intersterility groups: western North American P, eastern North American P, European P, North American S, Scandinavian S, Italian S, and Italian F. This is the first report on differentiation between eastern and western North American P isolates as well as between northern and southern European S isolates. Successful amplification of one dry basidiocarp suggests that random amplified polymorphic DNAs may be used to improve epidemiological and population studies of this pathogen. Key words: species complex, genetic variability, strain typing, forest pathology, polymerase chain reaction.
Effect of nutrition on susceptibility of cucumber, eggplant, and pepper crops to Botrytis cinerea
Authors: Elad Y. , Yunis H. , Volpin Hanne
Published: April 2011

Parthenocarpic cucumbers were grown in polyethylene tunnels under commercial conditions and fertilized with N – P – K 7:3:7%. During two winter seasons when nitrate level in the fertilizer was low, the addition of potassium to the fertilizer significantly reduced the incidence of fruit grey mould caused by Botrytis cinerea Pers.:Fr. by 27 – 33%, whereas adding calcium generally reduced grey mould by 35 – 50%. The fungicide treatments, diethofencarb and carbendazim (at 0.25 g∙L−) reduced grey mould by 39 and 50%, respectively. In the 2nd year stem infection with B. cinerea was decreased by 50, 50, or 60% by treatment with potassium, fungicide, or calcium, respectively. Only the calcium treatment was significantly different from the basic fertilizer control. Calcium treatments were effective on cucumber crops only under high relative humidity at two out of four sampling dates. The effect of calcium could not be separated from high nitrate level associated with its use in cucumber plantings. Potassium enrichment reduced natural incidence of downy mildew (Pseudoperonospora cubensis). Neither ion reduced incidence of powdery mildew (Sphaerotheca fuliginea) in cucumber crops. Disease reduction and increased yield of an eggplant crop were obtained by the addition of calcium to the fertilizer. Grey mould of pepper was reduced by 50 – 60% by adding calcium, but pepper yield was not increased. A single application of calcium sulphate alone or with calcium dihydrogen phosphate to glasshouse plants resulted in a reduction of grey mould in pepper and eggplant artificially inoculated with B. cinerea. Key words: Botrytis cinerea, Pseudoperonospora cubensis, Sphaerotheca fuliginea, calcium, nitrate, potassium.
Microspore and pollen development in six male-sterile mutants of Arabidopsis thaliana
Authors: Dawson J. , Wilson Z. A. , Aarts M. G. M. , Braithwaite A. F. , Briarty L. G. , Mulligan B. J.
Published: April 2011

Five new recessive male-sterile mutants of Arabidopsis thaliana were isolated following seed mutagenesis by X-rays and ethyl methanesulfonate. The cytology of plants homozygous for the msY and msW mutations suggested that pollen development in these lines became abnormal at or before meiosis. The msK mutation caused faulty timing of synthesis or turnover and distribution of callose. In plants homozygous for the msZ mutation, pollen development failed at a late stage. In wild-type plants, the stamen filament elongated just prior to anther dehiscence. In contrast, in the msZ mutant stamen elongation did not occur. Pollen in msH homozygotes was fertile, but anthers failed to dehisce. The msI mutant of J.H. Van der Ween and P. Wirtz (1968. Euphytica 17: 371 – 377) was included in the present study. Pollen development in this mutant failed shortly after microspore release from tetrads. Complementation tests confirmed that the ms mutations were at different loci. Reduced transmission of certain ms genes was observed. Key words: Arabidopsis thaliana, male sterile mutants, anther dehiscence, callose, inheritance.
Red spruce bud mortality at Whiteface Mountain, New York
Authors: Hadley Julian L. , Amundson Robert G. , Laurence J. A. , Kohut R. J.
Published: April 2011

Terminal bud mortality for shoots produced between 1982 and 1989 was measured for midcanopy branches of mature red spruce trees (Picea rubens Sargent) at two elevations on Whiteface Mountain, New York, U.S.A. Average terminal bud mortality ranged from 15 to 45% in different years, and there was no evidence for a biotic cause of bud mortality. Between branches on different trees, there was a negative correlation between frequency of terminal bud mortality for shoots produced between 1987 and 1989 and the percent change in current-year foliage biomass between 1987 and 1990. Branches with a high frequency of terminal bud mortality also tended to have a high proportion (> 50%) of 1990 shoots developed on adventitious branchlets. In late November 1990, terminal buds from most trees at 710–1120 m elevation were susceptible to freezing injury between −31 and −38 °C when cooled at 4 °C/h under laboratory conditions. Typical winter minimum temperatures at 700–1100 m elevation on Whiteface Mountain are within this range. In a recent controlled study of red spruce seedlings, high foliar nitrogen was associated with an increased risk of freezing injury to terminal buds in autumn. We found that red spruce on Whiteface Mountain had higher foliar nitrogen levels compared with red spruce at a much lower elevation in Maine. Based on these results, we advocate further research on the relationship between foliar nitrogen and bud freezing sensitivity in high elevation red spruce. Key words: Picea rubens, red spruce, bud mortality, freezing injury, nitrogen, red spruce decline.
Physiological indicators of nitrogen response in a short rotation sycamore plantation. II. Nitrogen metabolism
Authors: Tschaplinski Timothy J. , Norby Richard J.
Published: April 2011

American sycamore (Platanus occidentalis L.) seedlings were grown in the field under different urea–nitrogen fertilization regimes to identify nitrogen variables that characterize the growth response. Treatments included fertilization with 50, 150, and 450 kg N/ha, periodic fertilization (three times during the growing season) at 37.5 kg N/ha, and an unfertilized control. Leaf total nitrogen concentration was a poor indicator of plant growth response to nitrogen fertilization. Salt-extractable protein, nitrate, and free amino acid concentrations all trended upward by the end of the growing season as relative growth rate declined, but treatment differences were minimal. Leaf nitrate reductase activity was consistently higher in fertilized trees before substantial leaf senescence had occurred. When leaf loss was evident, all treatments had high levels of nitrate reductase activity. Aspartic acid and glutamic acid were the most prevalent free amino acids in leaves, whereas concentrations of amine-rich amino acids were low. Although several nitrogen variables, including foliar asparagine and glycine concentrations, were positively correlated with relative growth rate (r ≥ 0.7), no single variable closely reflected treatment differences in growth response. Key words: amino acids, nitrogen, nitrate reductase, sycamore.
Microtopography and methane flux in boreal peatlands, northern Ontario, Canada
Authors: Bubier J. , Costello A. , Moore T. R. , Roulet N. T. , Savage K.
Published: April 2011

Fluxes of methane were measured by a static chamber technique at hummock, hollow, and lawn microtopographic locations in 12 peatland sites near Cochrane, northern Ontario, from May to October 1991. Average fluxes (mg∙m−2∙d−1) were 2.3 (SD = 1.9) at hummocks, 44.4 (SD = 49.0) at hollows, and 15.6 (SD = 12.9) at lawns. Methane flux was negatively correlated with average water table position based on the 36 locations (r2 = 0.649, p < 0.001), with hummocks having a smaller flux than hollows or lawns, where the water table depth was < 25 cm. Peat samples from a bog hummock and hollow failed to produce methane during anaerobic incubations in the laboratory; samples from a poor fen hollow produced < 1.4 μg∙g−1∙d−1. The production decreased with depth but was greater than the rates observed during the incubation of samples from an adjacent hummock. Rates of methane consumption during aerobic incubations ranged from 1 to 55 μg∙g−1∙d−1 and were greatest in the surface layers and decreased with depth. Differences in methane emissions between hummocks and hollows appear to be controlled primarily by greater methane production rates in hollows compared with hummocks. Of secondary importance are the capacity of the peat profiles to consume methane during its transport to the peat surface and warmer temperatures at the water table beneath hollows compared with hummocks. Key words: peatlands, methane, bog, fen, decomposition.
Effect of osmotic stress on the respiratory properties of shoots and roots of Arnica alpina
Authors: Collier Donald E. , Cummins W. Raymond
Published: April 2011

Arnica alpina plants were exposed to 0.3 or 0.6 M sorbitol for 5 days to investigate the effect of long-term osmotic stress on the cytochrome and alternative respiratory pathways in both shoots and roots. Exposure to 0.3 M (−0.72 MPa) sorbitol significantly reduced growth in both shoots and roots. Increased alternative pathway activity was observed in shoots, exposed to 0.3 M sorbitol whereas increased cytochrome pathway activity, with a concomitant increase in the theoretical rate of ATP production, was found in the roots. Despite a reduction in shoot and root ethanol-soluble sugars, respiration was never substrate limited. These results suggest that the reduced demand for shoot growth energy was offset by an equally increased demand for maintenance energy. In roots, however, additional ATP production was required to meet the metabolic demands of exposure to 0.3 M sorbitol. Exposure to 0.6 M (−1.44 MPa) sorbitol completely stopped shoot and root growth and decreased respiration after only 1 day. In shoots, cytochrome pathway activity was inhibited, whereas in roots both pathways were transiently stimulated. By day 5, respiration along both pathways was significantly inhibited. The possible role of the alternative pathway as an energy overflow and an energy overcharge during osmotic stress is discussed. Key words: alternative pathway respiration, Arnica alpina, ATP, cytochrome pathway respiration, osmotic stress, respiration.
Dating the evolutionary radiations of the true fungi
Authors: Berbee Mary L. , Taylor John W.
Published: April 2011

In this paper we construct a relative time scale for the origin and radiation of major lineages of the true fungi, using the 18S ribosomal RNA gene sequence data of 37 fungal species, and then calibrate the time scale using fossil evidence. Of the sequences, 28 were from the literature or data banks and the remaining 9 are new. To estimate the order of origin of fungal lineages we reconstructed the phylogeny of the fungi using aligned sequence data. To compensate for the differences in nucleotide substitution rates among various fungal lineages, we normalized the pairwise substitution data before estimating the relative timing of fungal divergences. We divided the fungi into nine groups. We then calculated the average percent substitution for each group, and also the average for all the groups, for the time period beginning when the fungi diverged from a common ancestor and ending at the present. We used the ratios of group-specific percent substitutions to the average percent substitution to normalize our pairwise substitution data matrix. To infer the relative timing of the origin of lineages we superimposed the normalized percentages of nucleotide substitutions onto the parsimony-based phylogeny. Calibrating the rate of sequence change involved relating the normalized percent substitution associated with phylogenetic events to fungal fossils, the ages of fungus hosts, and ages of symbionts. These calibration points were consistent with a substitution rate of 1% per lineage per 100 Ma. Based on phylogeny and calibrated percent substitution, the terrestrial fungi diverged from the chytrids approximately 550 Ma ago. After plants invaded the land approximately 400 Ma ago, ascomycetes split from basidiomycetes. Mushrooms, many ascomycetous yeasts, and common molds in the genera Penicillium and Aspergillus may have evolved after the origin of angiosperm plants and in the last 200 Ma. Key words: fungus evolution, molecular clock, ascomycete phylogeny, basidiomycete phylogeny, 18S rRNA.
Mycorrhizal stimulation of plant parasitism
Authors: Sanders Ian R. , Koide Roger T. , Shumway Durland L.
Published: April 2011

Symbioses, intimate relationships between dissimilar organisms, are most often considered as two-partner interactions. In nature, however, plants can simultaneously interact with a number of symbionts such as the mutualistic mycorrhizal fungi and the parasitic angiosperm dodder. We found that successful shoot parasitism by dodder on plants in a field experiment occurred almost exclusively when the plant roots were colonized by mycorrhizal fungi. Under controlled conditions, life expectancy of dodder was significantly greater on mycorrhizal plants than on nonmycorrhizal plants. Furthermore, colonization of roots by mycorrhizal fungi increased the growth rate of dodder to 3.4 times the rate on nonmycorrhizal plants. The mycorrhizal effect on dodder growth occurred before the haustoria of dodder had succeeded in penetrating the host. These results suggest that colonization by mycorrhizal fungi had systemic effects on their hosts, which altered either the nature of prepenetration dodder signals or the levels of nutrients contained in host stem exudates. These findings could be important for understanding plant–parasite interactions. Key words: Abutilon theophrasti, Cuscuta pentagona, plant parasitism, vesicular–arbuscular mycorrhizas.
Condensed tannins in sainfoin. 1. A histological and cytological survey of plant tissues
Authors: Lees G. L. , Suttill N. H. , Gruber M. Y.
Published: April 2011

Sainfoin (Onobrychis viciifolia Scop.) organs and tissues were surveyed for the presence of proanthocyanidins or condensed tannin (CT) in an attempt to learn more about CT formation. Three histological methods were used: a vanillin–HCl stain to localize areas of CT formation through a distinctive cherry-red coloration of CT-containing cells; osmium fixation to further localize CT formation in cellular organelles using light microscopy; and fine localization and examination using electron microscopy. Cells containing CTs were found in relatively large numbers throughout the sainfoin plant in all organs except the roots. No CTs were found in the cotyledons or in some petals. Ultrastructural studies revealed that CTs are restricted to the vacuoles and appear to accumulate on the inner periphery adjacent to the tonoplast or in the centre of the organelle, possibly next to vacuolar invaginations. Key words: condensed tannin, proanthocyanidin, sainfoin, histology, transmission electron microscopy.
The development of the aleurone layer in canola (Brassica napus)
Authors: Groot Edwin P. , Caeseele Lawrence A. Van
Published: April 2011

The presence of the aleurone layer in developing seeds of Brassica napus becomes apparent about 22 days after pollination when examined with light and electron microscopic techniques. Prior to aleurone differentiation, the endosperm cellularizes centripetally to form characteristic columns of cells. The pigmented cell layer of the inner integument, which is present in dark-hulled seeds of Brassica, is just external to the aleurone. The first characteristic structures that become apparent inside the aleurone are spherosomes formed by the coalescence of small oil droplets. Shortly thereafter, the cell walls of the aleurone become markedly thickened relative to the surrounding cells. The aleurone cells of mature seeds contain lipid and protein reserves but lack starch. Development of the aleurone layer occurs first near the adaxial area and proceeds until the micropylar area finally differentiates. Endosperm chloroplasts have a characteristic lens shape when viewed in section with the electron microscope. They appear to congregate around a nucleus along with a small amount of cytoplasm causing an astroid-shaped aggregation of cytoplasm in the majority of endosperm cells but only transiently in the aleurone. DNA fluorometry and image analysis showed that aleurone nuclei are triploid; therefore the aleurone layer is derived from the endosperm. Key words: aleurone layer, endosperm, seed development, ploidy, anatomy, Brassica napus.