bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural changes in rapid-cycling Brassica rapa selected for differential waterlogging tolerance
Authors: Daugherty Christine J. , Matthews Sharon W. , Musgrave Mary E.
Published: December 2007

Two populations of rapid-cycling Brassica rapa L. selected for differential waterlogging tolerance and a commercially available standard population were compared in their structural responses to waterlogging. Rates of dry matter accrual were similar under drained conditions but were lower after 6 days of waterlogging, especially in the sensitive population. Chlorophyll content of leaves from the sensitive population was significantly lower than the tolerant population. Examination of the foliage by TEM after 4 days of waterlogging revealed large starch grains that apparently disrupted the grana stacks in the sensitive population. Root morphology also distinguished the populations. After 8 days of waterlogging, numerous adventitious roots were visible in the standard and tolerant populations but not in the sensitive population. No aerenchyma was detected by examination of root cross sections. Mitochondrial morphology was affected by waterlogging, resulting in elongate, branched organelles. Isozyme analysis of malic enzyme, malate dehydrogenase, glucose-6-phosphate dehydrogenase, and pyruvate decarboxylase revealed no differences due to population, treatment, or duration. Isozymes of alcohol dehydrogenase varied with duration of waterlogging, and isozyme forms of phosphoglucomutase were distinct depending on the population. The appearance of stress-specific structural features in populations of B. rapa is discussed in relation to differences in waterlogging tolerance. Key words: hypoxia, isozymes, aerenchyma, adventitious roots, waterlogging, starch.
Détermination de l'ébauche foliaire, du bourgeon axillaire et de l'entre-noeud chez le Manihot esculenta : étude microchirurgicale
Authors: Médard R.
Published: December 2007

A microsurgical study on Manihot esculenta shows that foliar initiation occurs more than two plastochrons before bulging out. Initiation of the axillary bud of the leaf occurs at the beginning of bulging out. Injuries produced along the path of the future procambial bundle of the older foliar initial create a delay in the bulging out of this initial, which will occur only after the bulging out of the following initial. This delay generates a reversal of the final vertical stem spacing of the two leaves that emerge from those two initials. Therefore, with each leaf bulging out, a preinternode appears above the first primordium. The vertical spacing of leaves does not necessarily result from the vertical spacing of initials. Moreover, the position of the foliar initial is affected by information moving in the apex, especially from the bulging out of the first primordium. The nature of this information is discussed and the results obtained are analysed in the light of the literature on phyllotaxy. Key words: cassava, leaf, foliar initiation, apical meristem, phyllotaxy, internode.
Mineral concentrations within cells of galls induced by Hemadas nubilipennis (Hymenoptera: Pteromalidae) on lowbush blueberry: evidence from cryoanalytical scanning electron microscopy
Authors: Bagatto Giuseppe , Shorthouse Joseph D.
Published: December 2007

Cryoanalytical scanning electron microscopy was used to examine cellular concentrations of K, P, S, Mg, Ca, Fe, Cu, Ni, and Au in a planed section of an insect gall induced by Hemadas nubilipennis on shoots of lowbush blueberry. Levels of K varied throughout tissues of the gall, with the highest levels within the cytoplasmically dense nutritive cells lining the larval chambers, storage nutritive cells, and peridermal cells. It is postulated that K increases the osmotic potential and size of nutritive cells, thereby facilitating larval feeding. Nutritive cells also contained elevated levels of P and S. Levels of Cu, Ni, Fe, and Au were elevated in epidermal tissues, especially near the stomata. Key words: gall, blueberry, minerals, cryoanalytical SEM, Hemadas nubilipennis, Vaccinium angustifolium.
Population structure and decay pattern of Phellinus tremulae in Populus tremula as determined by somatic incompatibility
Authors: Holmer L. , Nitare L. , Stenlid J.
Published: December 2007

Isolates of the wood-decaying basidiomycete Phellinus tremulae were obtained from four different stands of aspen Populus tremula in the south of Sweden. Studies were made of somatic incompatibility among all isolated within each site. No genet could be found in more than one tree. From one stand, two trees were felled and samples were taken from stem discs every half metre up to 13 m. Eight genets were isolated from the two trees, four in each tree. Fungal DNA was amplified from five isolates representing three different genets in one tree. The core sequence of M13 was used as primer. The results agreed with those of the somatic incompatibility test. Forty-five samples were taken from small twigs from healthy-looking branches and trees, and isolates of Phellinus tremulae were obtained from three of them. The likely route of infection of Phellinus tremulae in aspen is discussed. Key words: somatic incompatibility, Phellinus tremulae, Populus tremula.
Chilling effects on leaf photosynthesis and seed yields of Phaseolus vulgaris
Authors: Pena-Valdivia Cecilia Beatriz , del C. Luz , Lagunes E. , Perales R. Hugo R.
Published: December 2007

Three common bean cultivars (climbing ‘Negro Mecentral’, bushlike ‘Negro Mecentral’, and ‘Tendergreen’) were studied during seed maturity. A single dark period of a chilling treatment (4 °C, 12 h) resulted in a sizeable reduction of the photochemical and photosynthetic activities of the leaves during the seed maturity stage. Leaf net photosynthesis, transpiration rate, and stomatal conductance for water vapor were drastically reduced in ‘Tendergreen’ at 28 days after anthesis, but in bushlike ‘Negro Mecentral’ these values decreased until 30 days after anthesis. Chilling drastically reduced electron transport of freshly lysed chloroplasts isolated from bushlike ‘Negro Mecentral’ and ‘Tendergreen’ at 32 days after anthesis. This contrasts with climbing ‘Negro Mecentral’ plants, in which electron transport decreased progressively between 28 and 32 days after anthesis. Photophosphorylation rates at 32 days after anthesis were reduced by 31, 58, and 45% in climbing ‘Negro Mecentral’, bushlike ‘Negro Mecentral’, and ‘Tendergreen’ plants, respectively. Light-dependent proton uptake was more damaged in ‘Tendergreen’ (88%) at 32 days after anthesis than in bushlike ‘Negro Mecentral’ (31%) and climbing ‘Negro Mecentral’ (38%). Seed yield per plant tended to decrease with treatment in climbing ‘Negro Mecentral’ (45% at 32 days after anthesis) and in bushlike ‘Negro Mecentral’ (34% at 32 days after anthesis), whereas in ‘Tendergreen’ the yield apparently was not affected. However, seed weight and size of climbing ‘Negro Mecentral’ decreased following the treatment, while they increased in bushlike ‘Negro Mecentral’ and ‘Tendergreen’. Seed protein content increased dramatically at 28, 30, and 32 days after anthesis in treated bushlike ‘Negro Mecentral’ (52, 78, and 42%, respectively), but it did not change in climbing ‘Negro Mecentral’ and ‘Tendergreen’. In conclusion, the chilling effects on photochemical activities, seed yield, and seed composition of common bean plants at seed maturity vary according to cultivar and plant developmental stage. Key words: Phaseolus vulgaris, photosynthesis, chilling effect.
Phoma etheridgei sp.nov. from black galls and cankers of trembling aspen (Populus tremuloides) and its potential role as a bioprotectant against the aspen decay pathogen Phellinus tremulae
Authors: Hutchison Leonard J. , Chakravarty P. , Kawchuk Lawrence M. , Hiratsuka Yasuyuki
Published: December 2007

Phoma etheridgei is described and illustrated from isolates obtained from the bark of black galls and cankers of trembling aspen in Alberta. Comparisons are made with Phoma enteroleuca and several other mostly wood-inhabiting Phoma spp. using morphological, physiological, and molecular characteristics. A key is provided for the differentiation of Phoma spp. that could potentially be isolated from Populus wood. Phoma etheridgei produced antifungal compounds that were strongly inhibitory in vitro to the aspen decay pathogen Phellinus tremulae on agar, in liquid media and on aspen wood chips, and may play a role in the natural ecosystem as an antagonist to Phellinus tremulae. Key words: Phoma etheridgei, taxonomy, black gall, antifungal metabolites, biological control, Phellinus tremulae, Populus tremuloides.
Isolation of peroxidase from bean and millet compared with that from peanut
Authors: Huystee R. B. van , Malko M. , Wen K. , Gijzen M.
Published: December 2007

Purification of peanut (Arachis hypogaea L.) peroxidase in milligram amounts is feasible through its isolation from spent medium of cultured cells. Using the same and modified approaches for another cultured dicot and a monocot yielded only low amounts of peroxidase for bean (Phaseolus vulgaris) and millet (Setaria italica Beav.). We showed that the procedures used for millet rendered a purer fraction than the commercial crude fraction available for horseradish. The data suggest that cultured peanut cells in suspension culture are an ideal system for isolation of peroxidase in terms of the ease of purification and yield. Key words: peanut, bean, millet, peroxidase, purification, tissue.
Monoplastidy in spermatogenesis of Lycopodium obscurum
Authors: Renzaglia Karen Sue , Maden Angel R. , Duckett Jeffrey G. , Whittier Dean P.
Published: December 2007

Unlike Lycopodium laterale, which is polyplastidic during spermatogenesis, Lycopodium obscurum exhibits monoplastidy beginning in the early proliferative stages of antheridial development. Previous cell generations are polyplastidic and plastid fusion involving connective cylinders establishes the monoplastidic condition. Plastid and nuclear divisions are coordinated in L. obscurum with the plastids positioned at opposite poles prior to spindle development. Unlike monoplastidic cell divisions with morphogenetic plastid migration and polarity in other lycophytes, mosses, and hornworts, however, the spindles in L. obscurum do not originate from the plastid envelopes but from endoplasmic reticulum positioned against the plastid. In the final divisions, spindle microtubules emanate from structurally defined microtubule organizing centers that develop between the plastids and nucleus. Preceding the appearance of centrioles in the spermatid mother cell, the centrosomes comprise electron-dense granular matrices with associated vesicles and endoplasmic reticulum. Among archegoniate microtubule organizing centers, the discrete acentriolar centrosomes of Lycopodium most closely resemble the microtubule organizing centers in moss spore development and the polar organizer of liverwort mitosis. Key words: annulate lamellae, centrosome, Lycopodium, microtubule organizing center, monoplastidy, plastid dividing ring.
Microtubular configurations during endosperm development in Phaseolus vulgaris
Authors: XuHan X. , Lammeren A. A. M. Van
Published: December 2007

Microtubular cytoskeletons in nuclear, alveolar, and cellular endosperm of bean (Phaseolus vulgaris) were analyzed immunocytochemically and by electron microscopy to reveal their function during cellularization. Nuclear endosperm showed a fine network of microtubules between the wide-spaced nuclei observed towards the chalazal pole. Near the embryo, where nuclei were densely packed, bundles of microtubules radiated from nuclei. They were formed just before alveolus formation and functioned in spacing nuclei and in forming internuclear, phragmoplast-like structures that gave rise to nonmitosis-related cell plates. During alveolus formation cell plates extended and fused with other newly formed walls, thus forming the walls of alveoli. Growing wall edges of cell plates exhibited arrays of microtubules perpendicular to the plane of the wall, initially. When two growing walls were about to fuse, microtubules of both walls interacted, and because of the interaction of microtubules, the cell walls changed their position. When a growing wall was about to fuse with an already existing wall, such interactions between microtubules were not observed. It is therefore concluded that interactions of microtubules of fusing walls influence shape and position of walls. Thus microtubules control the dynamics of cell wall positioning and initial cell shaping. Key words: cell wall, cellularization, endosperm, microtubule, Phaseolus vulgaris.
The morphology and ultrastructure of Caytonanthus
Authors: Osborn Jeffrey M.
Published: December 2007

The morphology and ultrastructure of Caytonanthus arberi pollen organs and pollen, collected from the Middle Jurassic, Cayton Bay locality of England, are described. Pollen organs consist of flattened rachises with suboppositely branched pinnae, which bear terminal synangia. The synangium is covered with a two-zoned (fibrillar and amorphous) cuticle. The locule of each pollen sac is lined with a lamellated tapetal membrane and contains numerous pollen grains and orbicules. Grains are small, monosulcate, and bisaccate. Exine ornamentation of the proximal wall is psilate, while distally the apertural membrane is scabrate. The exine is composed of a thick, lightly staining sexine and a thin, darkly staining nexine. The sexine is tectate-alveolate laterally, becoming nearly homogeneous medially. The infratectal alveolae are robust and are continuous with the endoreticular units of the sacci. Sacci are eusaccate, with endoreticulations attached only to the outer walls. Several immature grains have also been identified and indicate that the nexine is lamellate throughout and that infratectal alveolae and nexine lamellae are well developed prior to complete tectum synthesis. Saccus size and ultrastructure of Caytonanthus pollen are compared with those of other Late Paleozoic and Mesozoic seed ferns that produced saccate pollen (Callistophytales, Glossopteridales, Corystospermales) and found to be smaller and more extensively filled with thicker endoreticulations. Documentation of the eusaccate character state in Caytonanthus is also discussed regarding its phylogenetic implications. Key words: Caytonanthus, Caytoniales, Mesozoic, pollen, seed fern, ultrastructure.
Systèmes de croisement et fécondité chez le Sphagnum
Authors: Pujos José
Published: December 2007

Sexuality is most often preserved in Sphagnum while asexual reproduction remains responsible for the perennity and multiplication of the species. Sexual reproduction success was assessed for two diecious species and four monecious – polyecious species, using fertilization rates, reproduction rates, and success of the reproduction. The effects of different crossing processes on the preceding parameters were emphasized. Accordingly, gynoecium numbers, archegone numbers per gynoecium, and sporogonia occurrences were assessed in more than 3500 capitula. Variable distribution of gametangia within capitula in different species determines the success of sexual reproduction. An evolutionary interpretation of this variation in the distribution of gametangia is proposed. Key words: Sphagnum, crossing processes, polyecious, sexualization rates, reproduction success. [Journal translation]
Phenotypic characterization of the dwarf-4 mutant of lettuce
Authors: Waycott William , Mersey Brent
Published: December 2007

The single recessive mutant dwarf-4 (d-4) of lettuce (Lactuca sativa L.) was selected as a potential genetic source of resistance to premature stem elongation (bolting). This study was undertaken to define the mutant phenotype and to characterize its reaction to applied gibberellin (GA). Scanning electron micrographs of mutant and wild-type achenes revealed surface and subsurface aberrations in d-4, suggesting abnormal development. Observed mutant irregularities included (i) abnormal achene formation causing irregularly shaped seeds, (ii) delayed and irregular germination, (iii) delayed but normal leaf growth and leaf area, (iv) 66% reduction in stem height, (v) 50% reduction in shoot dry weight, (vi) 0.45% viable pollen formation, and (vii) 98.9% self-sterility. Applications of GA3 did not affect the delay in growth, floral sterility, or abnormal achene shape but did increase stem height and shoot dry weight to wild-type levels at maturity. Hand pollinations were able to decrease self-sterility to 93.6%. Component analysis of mutant and wild-type achenes revealed d-4 had 32% lower fatty acid levels. There were no differences in carbohydrates, cell wall constituents, and moisture levels, although higher levels of protein and inorganic compounds were found. The observed d-4 phenotype suggests that its genetic lesion is not directly tied to irregularities of gibberellin biosynthesis but has some other genetic basis. Key words: Lactuca sativa, SEM, germination, stem elongation, sterility.
A taxonomic reappraisal of the genus Ceriosporopsis based on ultrastructure
Authors: Yusoff M. , Jones E. B. G. , Moss S. T.
Published: December 2007

This paper reports results of ultrastructural studies of ascospores and their appendages in Ceriosporopsis caduca, Ceriosporopsis circumvestita, and Ceriosporopsis capillacea. Ceriosporopsis caduca and C. capillacea have polar appendages that arise as outgrowths of the spore wall. The exosporium, which initially extends over the polar appendages, later forms a collar at their base. In C. circumvestita, the sheath is mesosporial in origin and is chambered; an exosporium is absent, and there is no collar at the base of the appendage. Because of the difference in ascospore appendage structure, C. circumvestita is transferred to a new genus Lautisporopsis. The taxonomy of the remaining species of Ceriosporopsis is reviewed, and comparisons are made with Bovicornua intricata. Key words: Ascomycotina, marine fungi, taxonomy, ultrastructure, Lautisporopsis.
Symptom expression and ethylene production in leaf blight of cotton caused by Alternaria macrospora and Alternaria alternata alone and in combination
Authors: Bashan Yoav
Published: December 2007

The interaction between the cotton leaf pathogens Alternaria macrospora and Alternaria alternata was studied using dual inoculation at dosages (≈ 103 spores/(mL ∙ pathogen)) that did not produce symptoms with either pathogen alone. This dual inoculation produced the typical disease symptoms (spots and shedding) and disease severity similar to inoculation with 104 spores/mL of A. macrospora alone. Neither pathogen produced ethylene in culture; however, they induced production of ethylene concentrations by diseased tissue that were correlated to both disease severity and leaf shedding. Plants infected by both pathogens produced the highest concentration of ethylene. Leaf discs either from leaves exhibiting symptoms or from symptomless infected leaves produced similarly high concentrations of ethylene. Inoculation of any site of the leaf with A. macrospora alone or with both pathogens resulted in shedding of the leaf. Pretreating inoculated plants with several ethylene inhibitors or an auxin decreased ethylene production, disease severity, and leaf shedding. Alternaria alternata apparently triggers symptom expression by A. macrospora in leaf blight disease of Pima cotton, and disease is manifested by the production of ethylene that leads to the typical leaf shedding symptom. Key words: Alternaria macrospora, Alternaria alternata, cotton leaf blight, defoliation, ethylene, fungus – fungus interaction, leaf spot of cotton, symptomless infections, virulence.
Patterns of vegetation and water chemistry in peatlands of the west-central Wind River Range, Wyoming, U.S.A.
Authors: Cooper David J. , Andrus Richard E.
Published: December 2007

Seventeen peatland complexes were investigated in a 2000-ha study area in the Barnes Lake region of the west-central Wind River Range in Wyoming, U.S.A. Sites ranged in elevation from 2970 to 3200 m. The peatlands are generally less than 2 ha in size and are supported by groundwater flow systems. Seventeen plant community types are recognized using two-way indicator species analysis and Braun-Blanquet table methods, including 4 aquatic communities, 6 peatland expanse communities, and 7 peatland margin communities. Surface water in the study area is neutral to slightly acidic with very low cation concentrations. The water pH and flora indicate rich fen conditions, while the cation concentrations are more comparable to poor fens or even bogs. We propose calling the study area peatlands transitional rich fens, which are fed by mineral-poor water. The chemical composition of surface waters was found to be similar among different communities. Patterns of plant species and plant community distribution are a function of the water table depth and duration gradient and flow rates of the water supply. The rich – poor and peatland expanse – peatland margin gradients that reflect nutrient gradients do not appear to be important in the study area. Key words: fens, peatlands, Wyoming, Rocky Mountains, water chemistry, subalpine, alpine.
Ultrastructural studies on the embryo sac of Viscum minimum: II. Megagametogenesis
Authors: Zaki M. , Kuijt J.
Published: December 2007

Embryo sac development of Viscum minimum was investigated using light and electron microscopy. Stages described involve uninucleate, binucleate, four-nucleate, and mature embryo sacs following cellularization. During the early stage of development, prior to mitosis, numerous small vacuoles are initiated in the cytoplasm of a uninucleate functional megaspore. The centrally located nucleus undergoes the first mitotic division and results in formation of two identical nuclei sharing a common cytoplasm. As the vacuole increases rapidly in size, the two nuclei become separated and move to opposite poles where the second mitotic division takes place. A remarkable elongation of the embryo sac is observed between the second and third mitotic division. Eventually, the embryo sac reaches its final length, two-thirds of the length of the ovary, at cellularization. Elongation of the embryo sac is closely related to the increase in vacuole size. Factors involved in vacuole formation and in the elongation of the embryo sac are discussed along with changes accompanying the transition from a sporophytic to a gametophytic pattern of development. Ultrastructural studies on the mature embryo sac, following cellularization, suggest that the egg cell is the least active cell in the megagametophyte. On the other hand, the synergids appear metabolically very active, being rich in plastids, mitochondria, dictyosomes, numerous vesicles, polysomes, and reserves. The central cell is the largest cell in the embryo sac. In a mature embryo sac the central cell has two adjacent nuclei, suggesting that fusion of the nuclei is completed following pollination and fertilization. The antipodals possess a complete set of organelles, numerous free and aggregated ribosomes, and endoplasmic reticulum. It is believed the antipodals play a significant nutritive role during the development of the embryo sac of V. minimum. Modification of the wall between antipodals and central cell and its role in nutrient transportations are discussed. Key words: embryo sac, embryogenesis, gametogenesis, megagametogenesis, mistletoes, ultrastructure.
Ochroconis humicola causing muscular black spot disease of Atlantic salmon (Salmo salar)
Authors: Schaumann K. , Priebe K.
Published: December 2007

A dematiaceous hyphomycete was isolated from black discoloured areas of the somatic musculature of a specimen of Atlantic salmon. The fungus caused an endogenous mycosis and obviously must be classified as a facultative or opportunistic pathogen of marine fish. The optimum temperature for the strain was in the range between 20 and 25 °C, and the temperature tolerance for growth ranged from 10 to almost 37 °C. The morphological and physiological investigation revealed that the pathogen belongs to the genus Ochroconis de Hoog et von Arx, which is synonymous with Scolecobasidium Abbott. However, the definite species identification raised some difficulties, because the characteristics of our pathogenic isolate H 14 670 variably matched with at least four of the known species within the Ochroconis – Scolecobasidium — Dactylaria complex, i.e., O. humicola, O. constrictum, O. gallopavum, and O. simplex. Because of this multispecies affinity and taking into account the actual confused taxonomic state within this group of hyphomycetes, especially with regard to the pathogenic strains, the identification of the present isolate as O. humicola remains with some reservation. Key words: Atlantic salmon (Salmo salar L.), Dactylaria, fish disease, marine fungi, Ochroconis humicola, opportunistic fungi, Scolecobasidium.
Interactive effects of light and stratification on the germination of some British Columbia conifers
Authors: Li X. J. , Burton P. J. , Leadem C. L.
Published: December 2007

Pregermination stratification treatment was generally more important than the effects of light on seed germination by 14 conifer species and varieties native to British Columbia. Nevertheless, there were some strong species differences in the response of germination to light. Final germination percentage after 21 days (28 days for Abies spp.) for both stratified and unstratified seeds of Picea glauca, Picea sitchensis, and Tsuga heterophylla showed no response to light during germination. Seed germination by Abies grandis, Pinus contorta var. contorta, Pinus contorta var. latifolia, Pinus ponderosa, Pseudotsuga menziesii var. glauca, and Pseudotsuga menziesii var. menziesii responded positively to light if unstratified but was not significantly affected by light when stratified. For Thuja plicata seeds, germination responded positively to light regardless of stratification pretreatment. Light appeared to reduce germination of stratified seeds of Abies amabilis, Abies lasiocarpa, Larix occidentalis, and Pinus monticola, although stratification conditions for these species were suboptimal. The germination rate of stratified seeds of all species and unstratified seeds of most species was increased by light. Results showed no significant relationship between germination response to light and shade-tolerance ranking or mean seed weight of the species. In six seed lots of Pinus contorta var. latifolia, however, we detected a weak negative correlation between mean seed weight and unstratified light responsivity measured after 1 week but a significant positive correlation when measured after 3 weeks. Very low light levels in closed-canopy forests or in the forest floor may prolong tree seed germination but are unlikely to constrain final germination levels after most seeds have been naturally stratified by moist, cool winter conditions. The importance of differences in the rate and timing of tree seed germination under natural conditions remains to be demonstrated. Key words: conifer biology, forest regeneration, light response, lodgepole pine, Pinus contorta, seed germination, stratification.
Colonization dynamics of algae in small artificial ponds
Authors: Williams D. Dudley , Tavares-Cromar Annette , Coleman J. R. , Kushner D. J. , Happey-Wood Christine M.
Published: December 2007

The arrival, establishment, and growth of a variety of algae were studied in a series of newly established, small (48.5 L) artificial ponds located at three sites of differing characteristics in southern Ontario, Canada: open field, edge of woods, and deep woods. Algal colonization was most rapid at the open site, within 4 days of the ponds being filled, and was slowest at the deep woods site, presumably because of a filtering effect of the surrounding terrestrial vegetation. The patterns of algal colonization and subsequent population abundances were consistent among the ponds, despite very considerable variation in both their physical and biological environments (e.g., among ponds over the 2 years of study, conductivity ranged from 20 to 890 μS, pH from 6.4 to 10.7, dissolved oxygen from 0 to 13.5 mg ∙ L−1, and water temperature from 5 to 29.8 °C). The first colonizers were airborne microchlorophytes, particularly a species of Chlorella, which may have been favoured by clear water (high light) conditions, lack of competition, and an ability to tolerate low nutrient levels. Chlorella populations declined within 1 or 2 weeks, depending on site, coincident with an increase in the numbers of a species of Synechococcus, a cyanobacterium. Synechococcus dominated all the pond types at all three sites thereafter, although its abundance was strongly correlated with water temperatures. In their 2nd year, undisturbed mature ponds developed encrusting algae, especially Rhizoclonium and Oedogonium, on their walls. In years 1 and 2, the densities of Synechococcus in both the new and mature ponds, respectively, were positively correlated with the larval densities of the dominant mosquito species Culex restuans. Synechococcus was the primary item in the diet of these insects. Key words: colonization, algae, habitat variability, Synechococcus sp., Chlorella sp., artificial ponds.
Nuclear ribosomal internal transcribed spacer phylogeny and host diversity in the coelomycete Phomopsis
Authors: Rehner Stephen A. , Uecker Francis A.
Published: December 2007

Species concepts in Phomopsis are based primarily on host association because morphological and cultural characters are generally insufficient for species diagnosis. Increasingly, there are reports that some species of Phomopsis are not host restricted but are capable of infecting several or more taxonomically unrelated host genera. Phylogenetic analysis of nuclear ribosomal DNA internal transcribed spacer sequences (ITS1 and ITS2) for 43 North American and Caribbean strains of Phomopsis isolated from diverse plant hosts and geographic origins resolved three clades, provisionally termed groups A, B, and C. Group A consists of isolates from shrubs and trees originating primarily from eastern North America. Group B includes isolates from woody and herbaceous plants that originate from tropical to subtropical regions and produce paraphyses among their conidiogenous cells. Group C occurs primarily on herbaceous plant hosts, including agricultural field crops, and is widely distributed throughout temperate to subtropical North America. Isolates from Europe and Asia may be significantly different in ITS sequences compared with North American isolates. The diversity of host taxa associated with terminal clades in the ITS phylogeny suggests that either Phomopsis species infect more than one host or host switching occurs frequently during speciation. Key words: Ascomycotina, coelomycetes, Diaporthe, ITS, molecular phylogeny, Phomopsis.
Budding patterns during the cell cycle of the maize smut pathogen Ustilago maydis
Authors: Jacobs Charles W. , Mattichak Stephen J. , Knowles James F.
Published: December 2007

Haploid sporidia of the dimorphic phytopathogen Ustilago maydis (D.C.) Corda reproduce by budding once each cell cycle. Homogeneous log-phase sporidial cultures were generated by serial passage in liquid culture, and the growth characteristics and percentages of budded cells were determined for the cultures. The characteristics of budding were determined for individual cells by light and electron microscopy. Buds emerged only from the poles of mother cells, and cells could select either a previously used bud site, or a new bud site, each cycle. Time-lapse photomicroscopy indicated that, on solid medium, the first two buds emerged from new cells at a point distal to the site of attachment to the mother cell. In subsequent cell cycles, the buds tended to emerge from alternate poles of the mother cell. The cells used multiple bud sites at each pole. In addition, transmission and scanning electron microscopy revealed a series of annulations (bud scars) at the base of some buds, indicating that cells also used the same budding site many times. This versatility in selecting bud sites indicates that budding likely depends on complex regulatory pathways for determining cellular polarity. Key words: Ustilago maydis, bud, polarity, cell cycle, morphogenesis, yeast.
Race structure and dynamics in populations of Phytophthora infestans
Authors: Andrivon D.
Published: December 2007

The structure and dynamics of races of the potato late blight pathogen Phytophthora infestans in several populations collected worldwide during 1966–1993 were investigated using mathematical estimates of phenotypic diversity (Shannon and Rogers indices) and of virulence complexity. As expected, the highest diversity of races was found in central Mexico, whereas European and other American populations had consistently lower numbers of races and were usually dominated by one or a few phenotypes. Rogers indices were generally close to 0.5 when calculated for populations collected over successive years from the same area and for populations from neighbouring regions collected at the same period of time, indicating that some geographical and temporal structuring was the rule. This is consistent with a metapopulation structure for P. infestans and provides evidence for evolutionary patterns driven by founder effects. The mean number of virulence genes per race was highly variable among populations. Unnecessary virulences were frequent in most if not all populations. In all populations investigated, the rarest virulence genes were found in highly complex races, indicating a predominant influence of mutation events on race evolution. Key words: potato, late blight, virulence, diversity, complexity, population structure.
Isolation and lectin-binding properties of barley epidermal and mesophyll protoplasts
Authors: Struck C. , Rohringer R. , Heitefuss R.
Published: December 2007

Protoplasts from primary leaves of barley (Hordeum vulgare L.) were obtained by enzymatic digestion and fractionated by discontinuous density gradient centrifugation to yield highly enriched fractions of mesophyll and epidermal protoplasts. A characterization of both protoplast types resulted in a clear differentiation of the outer protoplast surfaces. The protoplasts were examined for affinity to various lectins by agglutination tests and by labeling with lectin – fluorescein isothiocyanate conjugates. Both types of protoplasts agglutinated with soybean lectin. Fluorescein isothiocyanate-labeled soybean lectin was uniformly distributed on the protoplast surface. Mesophyll protoplasts, but not protoplasts from the epidermis, were agglutinated by Concanavalin A. Both types of protoplasts exhibited fluorescence labeling with Concanavalin A – fluorescein isothiocyanate conjugate. This label often showed a patchy distribution on the protoplast surface. Tetragonolobus lectin and β-D-glucosyl Yariv artificial antigen agglutinated mesophyll but not epidermal protoplasts. One of three tested monoclonal antibodies with specificity for arabinogalactans had affinity to the surface of mesophyll and epidermal protoplasts. Key words: agglutination, arabinogalactan protein, cell surface, epidermal protoplasts, fluorescence labeling, lectin.
Dependency of cone production on tree dimensions in Abies mariesii
Authors: Seki Takeshi
Published: December 2007

Dependency of cone production on tree dimensions was examined in Abies mariesii trees that had developed undamaged crowns. The total and maximum numbers of cones produced by a tree for the last 8 years both had allometric relationships with the square of the trunk diameter just below the lowest living branch (DB2). The estimated number of cones produced during the most recent 17 years on the main branch axes showed a positive correlation with the square of the trunk diameter just below the whorl developed in 1979, 1969, or 1959, while no such relationship was found with DB2. The number of cones produced on a branch was constrained by the square of the branch diameter. I suggest that the number of cones is regulated by the amount of dry matter accumulated in the neighboring trunk and branches where the cones are produced rather than the whole amount of dry matter in the tree. Key words: Abies mariesii, cone production, tree dimensions, trunk diameter, branch diameter.
Allozymic uniformity in Iris lacustris (dwarf lake iris) in Wisconsin
Authors: Simonich Michael T. , Morgan Michael D.
Published: December 2007

Iris lacustris Nutt. is a federally listed threatened species in Canada and the United States and is currently under consideration for active conservation management. The species is restricted to the shores of the western Great Lakes region and to a very narrow habitat type. Reproduction is almost exclusively by vegetative ramets. Limited sexual reproduction occurs after primarily geitonogamous pollination, although the plant is primarily selfed. Enzyme electrophoresis was used to determine the extent of genetic variation within and between Wisconsin populations. Ten enzymes coded by 22 putative genetic loci were examined. All nine populations were found to be monomorphic at the 22 loci for the same suite of isozymes. Heterozygosity was not detected at any loci. The apparent genetically depauperate nature of the species is addressed with regard to life history and reproductive biology. Implications for conservation management are addressed. Key words: Iris lacustris, threatened, isozyme, monomorphic.
L'influence de divers caractères architecturaux sur l'apparition de la fourche chez le Fagus sylvatica, en fonction de l'absence ou de la présence d'un couvert
Authors: Nicolini Éric , Caraglio Yves
Published: December 2007

A qualitative architectural analysis conducted on young beech (Fagus sylvatica L.), benefiting from the protection of a leaf canopy or exposed to full sunlight, revealed architectural characteristics susceptible of influencing the arrangement of vertical lateral axes entering in direct competition with the trunk and contributing to the formation of forked axes. The distinct structures of the forked trees are dependent on the absence or the presence of a superior forest canopy. Forks are formed when the following events occur in nature: monocyclic growth (formation of a single growth unit per year) and polycyclic growth (formation of numerous growth units per year) of the terminal meristem originating from the main axis, destruction of this terminal meristem, and large increases or decreases in the annual growth rate. None of these characteristics alone will determine the arrangement of a forked branch. Nonetheless, the annual fluctuations in growth rate seem to have the strongest influence. A quantitative analysis conducted on two 18-year-old groups exposed to either full sunlight (no canopy) or shade (under dense high forest) revealed that the frequency in vertical lateral axes is greater in full sunlight (0.18 – 0.45) than in shade (0.03 – 0.1). Similarly, the percentage of polycyclic shoots is greater in full sunlight (51%) than in shade (14%). However, this polycyclic growth does not seem to have a direct influence on the formation of vertical lateral axes. On the other hand, there may be an intermediary influence on apical mortality since in full sunlight the percentage of seasonally traumatized stems is greater (31%) than in shade (21%). The apical mortalities seem to stimulate the organization of the vertical branches. However, this formation of vertical lateral axes seems mainly controlled by the fluctuations in annual growth rates and more specifically by the rate of growth reached by the plant. In full sunlight, the annual stems have an average size (40 – 75 cm) notably superior to 50 cm. It is beyond this threshold of development that the observed trees produced greater annual frequencies in the appearance of vertical lateral axes. In the shade, the average size of annual stems ranged from 20 to 55 cm, but seldomly surpassed 50 cm. The annual frequency in the appearance of vertical lateral axes is negligeable. Key words: beech, Fagus sylvatica, architecture, forked branch, growth, forest canopy. [Journal translation]
Taxonomic studies of Achnanthes (Bacillariophyta) in freshwater maritime antarctic lakes
Authors: Oppenheim D. R.
Published: December 2007

Eleven species of Achnanthes from Signy Island, South Orkney Islands are described including one new species. Benthic algal material from a range of shallow lakes of varying trophic status was examined by light microscopy and scanning electron microscopy. Detail of morphology is provided with an overview of the taxonomic literature for each species. In all cases source descriptions are cited, and where possible holotype and lectotype material was examined. The variation between populations inhabiting different lakes is considered. An examination of the geographical distribution of Achnanthes in southern latitudes from the literature confirms numerous records of widespread occurrence in freshwater environments in sub-antarctic regions but not from higher latitudes. Key words: Achnanthes, Antarctic, taxonomy, benthic, phytogeography.
Clonal reproduction of riparian cottonwoods in southern Alberta
Authors: Rood Stewart B. , Hillman Craig , Sanche Trevor , Mahoney John M.
Published: December 2007

From 1990 to 1993, 690 small cottonwood saplings were excavated along four rivers in the Oldman River Basin to determine their method of origin. Overall, 52% began as seedlings while 48% originated through clonal mechanisms, of which 30% (of the total) were root suckers, i.e., adventitious shoots from preexisting roots, and 18% were shoot suckers, i.e., new shoots originating from buried shoots. The shoot suckers arose primarily through (i) flood training, i.e., new shoot emergence from young shoots that had been toppled and buried during flood events, and (ii) shoot regrowth following decapitation by ice scouring or animal browsing. Only two saplings originated through cladoptosis, propagation from excised shoot fragments. The proportion of seedlings versus clonally established shoots varied somewhat across years and sites. Within a site, saplings near the river's edge were more commonly seedlings, whereas saplings further from the river were more commonly root suckers. Three cottonwood species occurred in the forests studied and their reproductive strategies varied somewhat. Unlike the balsam poplar (Populus balsamifera), narrowleaf cottonwood (Populus angustifolia), and interspecific hybrids, the prairie cottonwood (Populus deltoides) did not propagate through root suckers; all species produced seedlings and shoot suckers. This study demonstrates that clonal reproduction has the potential to contribute to the regeneration of riparian cottonwood forests in southern Alberta. The contribution through clonal propagation complicates the forest population structure and should be considered in programs to conserve the remaining riparian cottonwood forests in southern Alberta and elsewhere in North America. Key words: Populus, cottonwoods, hybrid poplar, reproduction, clones, suckering, seedlings.
Evaluation of the taxonomic status of Antennaria bayardi, Antennaria brunnescens, and Antennaria foggii (Asteraceae : Inuleae)
Authors: Chmielewski Jerry G.
Published: December 2007

Classificatory discriminant analysis was used as an analytical technique not only to classify specimens of Antennaria gaspensis, Antennaria isolepis, Antennaria media, Antennaria pulvinata, Antennaria rosea, and Antennaria umbrinella but also to define and to evaluate the classification criterion. The classification criterion was subsequently used to identify collections of Antennaria bayardi, Antennaria brunnescens, and Antennaria foggii with one of the previously defined species. The latter species were consistently classified to the western Rocky Mountain species A. pulvinata. The disjunct Newfoundland populations of A. pulvinata represent in part the polyploid, apomictic component of this typically western species. The eastward migration of A. pulvinata probably occurred during the Wisconsonian glacial period. Population numbers of A. pulvinata in Newfoundland support the recognition of the species as threatened. Habitat destruction is the single most important factor threatening the survival of this species in Newfoundland. Key words: Antennaria pulvinata, Asteraceae, Newfoundland, disjuncts, limestone.
Genetic diversity and population structure of red spruce (Picea rubens)
Authors: Hawley Gary J. , DeHayes Donald H.
Published: December 2007

Allozyme variation at 36 loci was estimated for 19 populations of red spruce (Picea rubens Sarg.) from throughout its natural range. Average estimates of polymorphic loci (95% criterion), effective number of alleles per locus, and observed and expected heterozygosities are 23%, 1.13, 7.47%, and 7.89%, respectively. Mean genetic distance among populations is 0.007, and 93% of the genetic diversity resides within red spruce populations. Comparisons with other species indicate that red spruce is less genetically variable than most other north-temperate woody plant species. Observed heterozygosity varied significantly among geographic regions, with northern cool-temperate populations having the highest mean observed heterozygosity, followed by central montane populations, then southern isolated populations with the lowest observed heterozygosity. Regional differences in genetic variability could be due to several factors, including migration from different glacial refugia, introgression of red spruce with more genetically variable black spruce in areas of sympatry in the north, and genetic drift followed by higher than expected levels of inbreeding in small isolated southern red spruce populations. Based on genetic distance, northern cool-temperate red spruce are more closely related to nonintrogressed red spruce than to nonintrogressed black spruce, suggesting that introgression is not a major factor contributing to greater genetic variability in the northern portion of the red spruce range. Relatively high genetic differentiation among populations, higher than expected levels of inbreeding, and evidence of reduced gene flow among populations suggest that low genetic variability evident in southern red spruce populations may be a result of genetic drift followed by inbreeding. Key words: Picea rubens, genetic diversity, isozymes, population genetic structure.
The effects of watershed liming on the tissue chemistry of three co-occurring poor fen species
Authors: Rossell Irene Mackun , Raynal Dudley J. , Leopold Donald J.
Published: December 2007

We investigated the impact of watershed liming on elemental concentrations in the shrubs Myrica gale and Chamaedaphne calyculata and the sedge Carex stricta. We analyzed tissues from plants co-occurring in 1-m2 plots in limed and unlimed portions of an Adirondack poor fen for Al, B, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, N, Na, Ni, P, Pb, Se, V, and Zn. Within 2 years of liming, we found higher concentrations of Ca, Ni, and Zn and lower N, Na, and Mn in Chamaedaphne foliage; higher Fe, K, Mg, Ni, Pb, and Zn and lower Co and Mn in Chamaedaphne twigs; higher Mo and lower Al, B, Mn, and Ni in Myrica foliage; higher Al, Cr, and Mo and lower Cd, Mn, and Se in Myrica twigs; and higher Al and lower Co and Cr in Carex foliage. Clearly, each species was unique in its uptake and allocation of elements, which will influence the rate these elements cycle in this watershed after liming. Elements in Carex foliage changed the least after watershed liming, while those in Chamaedaphne twigs changed the most. However, the slow decay of Chamaedaphne litter will likely inhibit the release of accumulated elements, including Ca. Key words: peatlands, poor fens, liming, watershed, tissue chemistry, Adirondacks.