bluuebunny/crossref_metadata_2025 huggingface dataset:
Ascospore discharge in the annulate form of Hypoxylon truncatum
Authors: Tsuneda A. , Arita T.
Published: September 2008

Ascospore discharge in the annulate form of Hypoxylon truncatum (Schw.:Fr.) J. H. Mill, is preceded by the loss of the peridial wall covering of the ostiolar region. This is accomplished by way of a specialized mechanism which involves hyaline spongy tissue located between the outer amorphous and inner palisade wall layers of the perithecium. The exposed ostiolar projection becomes concealed by terminal bulbous cells of short hyphae that arise from nearby peridial cells. Disintegration of the ostiolar projection occurs concomitantly with the disappearance of these bulbous cells. By this time a large part of the pseudoparenchyma and most of the paraphyses in the centrum have degenerated to form a transparent gelatinous mass. Asci deliquesce and release mature ascospores within the perithecium just prior to ascospore discharge. The ascospores ooze out of the ostiole mixed with the gelatinous material and form either a massive spore ball or a spore tendril.
Shoot ontogeny in Arctostaphylos uva-ursi (bearberry): origin and early development of lateral vegetative and floral buds
Authors: Remphrey W. R. , Steeves T. A.
Published: September 2008

In the course of a general developmental study of Arctostaphylos uva-ursi (L.) Spreng. (bearberry), observations were made on the pattern of lateral bud initiation and development. Three types of foliar organs (foliage leaves, transitional leaves, and bud scales) are initiated by a vegetative shoot apex each year in a predictable sequence. A robust bud, initiated as a detached meristem and delimited by a shell zone, developed in the axil of each foliage leaf. Smaller, poorly developed buds, sometimes arising from tissues of the leaf base, developed in transitional-leaf axils, but they rarely persisted. Although scale axils seldom contained buds, there was evidence to suggest that buds may have started to form but soon became arrested. In the development of an inflorescence, small bracts were initiated by the terminal apex instead of foliage leaves or cataphylls. Flower buds were then initiated in the axils of the bracts and the terminal apex became inactive. The relative roles of shoot apex and subtending leaf primorida in regulating the development of buds are discussed.
Comparaison des aptitudes morphogénétiques des étamines fertiles ou stériles d'Actinidia chinensis cultivées in vitro
Authors: Brossard-Chriqui Dominique , Tripathi Bal Krishna
Published: September 2008

High frequency plantlet regeneration is obtained by means of in vitro culture of neoformed roots arising from Actinidia chinensis Pl. stamens. The favourable influence of zeatin upon bud initiation from roots is demonstrated. Potential differences between stamens coming from ♀ or ♂ plants are also shown. On the same medium, sterile stamens exhibit a greater rooting potential than fertile ones, but the latter have a more pronounced callusing efficiency. These differences are transmittable through dedifferentiation; neoformed roots of ♂ origin have a weak bud regeneration ability, whereas roots of ♀ origin give rise to callus and buds. The implications of such observations in regard to the endogenous contents of auxins and cytokinins and their relations with the ♀ or ♂ nature of the plants are discussed. The histological origin of the different kinds of regeneration are also examined and point to the preservation of rooting potential by the bundle sheath of the stamens and of budding potential by the pericycle of neoformed roots. These data are considered in relation to the recent literature.
Vascularisation de la fleur de Lysichitum camtschatcense (Araceae)
Authors: Barabé Denis , Labrecque Michel
Published: September 2008

Based on the floral vascular system, the authors analyse the problem of pseudomonomery and the intergeneric relationships within the Calloideae. The whitish hermaphrodite flowers have a perigone formed of four tepals. The androecium is composed of four stamens, but the structure of the gynoecium is more variable. Thus, among the flowers studied we observed bilocular ovaries with one ovule per cavity, bilocular ovaries where one of the two cavities had failed to develop, and unilocular ovaries with one or two ovules. The study of the vascular system shows that all of these gynoecia are composed of two carpels. In each of them we observed two dorsal bundles and two complex ventral bundles, each of these formed of two simple ventral bundles belonging to different carpels. Concerning the unilocular gynoecium, with one or two ovules, the presence of the bundles of the abortive carpel indicates that this gynoecium is pseudomonomerous. It is with the genus Symplocarpus that Lysichitum shares the greatest number of characters; their floral characteristics are particularly similar. In a previous study it was supposed that Symplocarpus, which has a unilocular ovary, was really monomerous. Now, the latest analyses of the flower of Lysichitum force us to reconsider this interpretation. The distribution of the floral characters indicates that Symplocarpus is advanced in comparison with Lysichitum.
Cytology of basidiospore germination, penetration, and early colonization of Phaseolus vulgaris by Uromyces appendiculatus var. appendiculatus
Authors: Gold R. E. , Mendgen K.
Published: September 2008

Cytological studies were done on a compatible interaction between Phaseolus vulgaris and Uromyces appendiculatus var. appendiculatus. The cytoplasm of germinated basidiospores contained numerous microbodies in close association with lipid bodies, vacuoles, and endoplasmic reticulum. A single, polar germ tube commonly developed from a germinating basidiospore. The germ tubes tended to grow toward or along the junction lines between host epidermal cells. Appressorium formation in ca. 75% of all observations occurred less than 3.5 μm away from the lines of juncture. A mucilaginous exudate was associated with germ tubes and appressoria along areas of contact between host and fungus. Epidermal wall papillae were often observed beneath basidiospores and appressoria but did not restrict entrance of the fungus. The fungus directly penetrated the epidermal cell and invaginated the host plasma membrane. The apex of the penetration peg expanded to form an ovate intraepidermal vesicle. Electron-opaque material occluded the penetration pore after migration of the usually binucleate protoplast into the vesicle. The intraepidermal vesicle developed apically and formed a multicellular primary hypha that initially was multinucleate and later became uninucleate or binucleate. The primary hypha then grew into adjacent epidermal cells, subtending palisade parenchyma cells and underlying intercellular spaces.
Inoculation of in vitro cultivated sugarcane with smut (Ustilago scitaminea)
Authors: Fereol L.
Published: September 2008

Sugarcane plants of the cultivar B72 191 have been cultivated in tubes and inoculated with a pure culture of smut fungus (Ustilago scitaminea Sydow) in an otherwise microorganism-free environment. The parasite penetrates the tissues of the host. The plants thus infected produce symptoms of smut whip. The teliospores produced on these are viable and have retained their pathogenicity.
In vitro sexual and apomictic embryo sac development in Cenchrus ciliaris
Authors: DeGroote David K. , Sherwood Robert T.
Published: September 2008

Sexual and aposporous apomictic embryo sac development in three Cenchrus ciliaris genotypes was evaluated in situ and in vitro. An aseptic procedure was developed to culture involucres in which the pistils contained archesporial cells. Development of sexual embryo sacs or differentiation and development of nucellar cells continued, in vitro, through mature embryo sac formation in the three buffelgrass lines. A numerical assessment system was devised to evaluate the stage of embryo sac development in vitro or in situ. Theculture medium contained Murashige and Skoog mineral salts supplemented with 1 × 10−4 M FeEDTA, 5.6 × 10−4 M myo-inositol, and 8.8 × 10−2 M sucrose in 1% agar. The best culture conditions were a 14 h light: 10 h dark photoperiod at a 25:19 °C (light:dark) temperature. Generally, 50% or more of the cultured involucres contained mature embryo sacs in good to excellent condition, and these sacs were indistinguishable from field-grown material. The in vitro culture technique provides a method to study embryo sac development and physiologic regulation of apomixis in Cenchrus ciliaris.
The taxonomy of the Carex rosea group (section Phaestoglochin) in Canada
Authors: Webber J. M. , Ball P. W.
Published: September 2008

The Carex rosea group, part of section Phaestoglochin, consists of four species, three of which, C. appalachica Webber & Ball, C. rosea Schkuhr ex Willd., and C. radiata (Wahlenberg) Small, occur in Canada. It is shown that some characters used to separate the species, i.e., perigynium length, colouration of the orifice of the beak, number of perigynia per spike, and length of the lowest infructescence bract, are unreliable. Other characters, such as the widths of the broadest leaves and fertile culms, width and degree of coiling of the stigmas, shape of the perigynium base, and position of the achene within the perigynium, were found to afford a reliable separation of the species. Analysis of mixed populations of C. rosea, C. radiata, and C. appalachica suggests that hybridization does not occur. The chromosome numbers of the three Canadian species were found to be as follows: C. rosea, n = 26; C. radiata, n = 29; and C. appalachica, n = 26. Distribution maps of the three species in North America are also given.
Recent forest development on Yellow Island, San Juan County, WA
Authors: Agee James K. , Dunwiddie Peter W.
Published: September 2008

Yellow Island, a small member of the San Juan Island group in Puget Sound, was nearly treeless at the beginning of the 20th century. A significant increase in woody species has since occurred. In the central forested area of the island, Douglas-fir (Pseudotsuga menziesii) is the dominant tree species, with four regeneration peaks (250, 150, 75, and 45 years) apparently related to forest fires. These fires were patchy and of moderate to low intensity, with a fire rotation of about 80 years. In the nonforested zones on the island, significant tree invasion has occurred in the last 20 years. Shrub invasion of these areas is believed to have begun sometime in the last 20–50 years. Recent tree invasion of the grasslands is independent of fire history and is associated with above-average summer precipitation. The invading trees have initial height growth similar to trees established in the 1930s in the forest zone but higher diameter growth. Recent grassland invaders (after 1970) have almost twice the annual diameter increment of the early invaders. This is hypothesized to be the result of amelioration of desiccating summer winds by the early invaders, extending the growing season for recently established trees. If significant grassland zones are to be maintained on Yellow Island, tree and shrub removal will be required.
Freeze-induced sap absorption in Acer pseudoplatanus: a possible mechanism
Authors: Milburn J. A. , O'Malley P. E. R.
Published: September 2008

Xylem sap pressure changes in response to imposed temperature regimes were studied using excised stems of young sycamore seedlings (Acer pseudoplatanus L). Experiments confirmed that a rapid decrease in sap pressure (inducing an uptake of water) occurred within the xylem core during freezing. The sequence was reversed by thawing. Measurement of wood diameter or bark thickness revealed no significant changes which might accommodate this sap during freezing. Indeed, investigation of the sapwood density showed an overall increase on freezing. The absorption of water in response to freezing was shown to be operative in deliberately killed tissue, although high tissue water content above about 60% disrupted the response. Experiments using twigs at suprafreezing temperatures induced sap exudation also, but it was only a small fraction of the amounts which could be expected after freeze-induced absorption. Apparently suprafreezing exudation can be explained by thermal expansion effects of gas and sap in the wood. A mechanism is proposed based on sap uptake induced by apoplastic ice formation in gas-filled spaces, such as fibre cells, which may also account for the familiar maple sap exudation.
Effects of CO2 enrichment and water stress on growth of Liquidambar styraciflua and Pinus taeda seedlings
Authors: Tolley Leslie C. , Strain B. R.
Published: September 2008

Mathematical growth analysis techniques were used to assess the possible interactive effects of atmospheric carbon dioxide enrichment and water stress on growth and biomass partitioning of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) seedlings. Plants were grown from seed under 1000 μmol∙m−2∙s−1 photosynthetic photon flux density at CO2 concentrations of 350, 675, and 1000 μL∙L−1 for 56 days. At this time, half the seedlings in each CO2 treatment had water withheld until plant water potentials reached about −2.5 MPa in the most stressed plants, while the remaining plants were well watered. At the end of the drying cycle, stressed plants were returned to well-watered conditions for a 14-day recovery period. The greatest effects of water stress on growth were seen following the recovery period and were most severe for sweetgum seedlings grown at the lowest CO2 concentration. For sweetgum seedlings in particular, the reduction of early seedling growth following exposure to a period of drought under normal atmospheric CO2 concentration was ameliorated by growing plants under elevated CO2, primarily because of maintenance of greater net assimilation rates following a period of stress. The data presented here suggest that a doubling of atmospheric CO2 concentration would enable sweetgum seedlings to become established in drier sites which are currently dominated by loblolly pine seedlings.
Analyse du système ramifié de Phaseolus vulgaris: particularités du gradient morphologique gemmaire
Authors: Debouck D. G.
Published: September 2008

An analysis of the branching pattern in a dwarf so-called determinate variety of Phaseolus vulgaris L. has been attempted. A distinctive organogenetic gradient displayed by the axillary buds is described. The number of leafy nodes on the first-order axillary branch, before its termination by a double raceme, decreases as its level of insertion on the main stem increases. This modification in the axillary organogenesis culminates in the appearance of the simple axillary raceme, apparently coinciding with the bracteal transformation at the next axil on main stem. However, not all the stages in the reduction of axillary structures were observed. These facts are discussed in relation to the concepts of comparative isomorphic development of main stems and first-order axes, and certain correlations regulating cauline morphogenesis.
Ultrastructural changes in host leaf cells caused by host-selective toxin of Alternaria alternata from rough lemon
Authors: Kohmoto K. , Kondoh Y. , Kohguchi T. , Otani H. , Nishimura S. , Scheffer R. P.
Published: September 2008

A pathotype of A. alternata with selective pathogenicity to rough lemon produces two or more substances with selective toxicity to the host. The major toxin was extracted from culture fluids with ethyl acetate and purified by several different chromatographic procedures. Toxin (10 ng/mL, 25 μL) was applied to leaves; within 24 h, water congestion and veinal necrosis were evident. The first toxin-induced change detected by electron microscopy was in the mitochondria; toxin at 1 μg/mL caused swelling, reduction in numbers and vesiculation of cristae, and decreases in electron density of the matrix. At 1 h after toxin treatment, the percentages of affected mitochondria in cells of several tissues were 18 in bundle sheaths, 9 in mesophyll cells adjacent to bundle sheath, and 9% in mesophyll cells remote from sheath. The number of affected mitochondria increased with time, until nearly 100% were affected at 6 h. No effects on other organelles were evident at 6 h. No ultrastructural changes were evident in cells of resistant leaves. The same changes in mitochondria were observed in pathogen-inoculated susceptible but not in resistant leaves by 24 h after incubation. The data indicate that the initial site of toxin action may be in the mitochondria.
Protein synthetic activity during normal pollen development and during induced pollen embryogenesis in Hyoscyamus niger
Authors: Raghavan V.
Published: September 2008

Protein synthetic activity during maturation, germination, and embryogenic phases of pollen grains of Hyoscyamus niger (L.) was investigated by means of autoradiography of incorporation of [3H]arginine, [3H]leucine, [3H]lysine, and [3H]tryptophan. Silver grain counts showed that during pollen maturation, peaks of incorporation of [3H]arginine and [3H]lysine occurred before the onset of vacuolation in the uninucleate pollen grains and as starch accumulation was initiated in the bicellular pollen grains. In the latter, labeled amino acids were mostly incorporated into the vegetative cell and very little appeared in the generative cell. [3H]leucine and [3H]tryptophan were not incorporated into uninucleate pollen grains at any stage of their development, although they were localized in the vegetative cell of bicellular pollen grains. In germinating pollen grains the nucleus of the vegetative cell, the generative cell, and sperms did not incorporate the isotopes. While the majority of pollen grains incorporated [3H]arginine, [3H]leucine, [3H]lysine, and [3H]tryptophan immediately after culture of anthers, during further periods of culture, protein synthetic activity persisted only in a small number of uninucleate, nonvacuolate, and densely staining "embryogenically determined" pollen grains confined to the periphery of the anther locule. Subsequent division of these pollen grains was accompanied by incorporation of [3H]arginine, [3H]leucine, and [3H]lysine into the vegetative cell or into both the vegetative cell and generative cell. It is suggested that, in contrast to the 3H-labeled amino acid incorporation pattern observed in pollen grains during their normal ontogeny, a significant change associated with embryogenic induction is the incorporation of [3H]leucine and [3H]tryptophan into embryogenically determined uninucleate pollen grains and of [3H]arginine, [3H]leucine, and [3H]lysine into the generative cell of bicellular pollen grains.
Roeslerina gen. nov. (Caliciales, Caliciaceae), an ally of Roesleria and Coniocybe
Authors: Redhead S. A.
Published: September 2008

Rosleria subterranea (Weinmann) Redhead comb, nov., commonly cited as R. hypogaea Thüm. & Pass, or R. pallida (Pers.) Sacc, is shown to have septate, pigmented ascospores. Roeslerina gen. nov. is proposed for R. radicella sp. nov. and R. microspora sp. nov., species with aseptate pigmentless spores. Scanning electron microscope photographs of all three reveal surface ornamentation that supports the inclusion of the species in the Caliciaceae based on other gross morphological features.
A new species of Aspergillus isolated from forest soil
Authors: Bissett John , Widden Paul
Published: September 2008

Aspergillus tardus sp. nov. is described from maple forest soil in southern Québec. The species is characterized by slow growth in culture and the production of pale vinaceous pigments in the walls of the conidia and conidiophores. The small, radiate, biseriate conidial heads and elliptical vesicles indicate an affinity with species in the Aspergillus versicolor group.
Teliospores of Entorrhiza casparyana (Ustilaginales): a correlated thin-sectioning and freeze–fracture study of endogenously dormant spores
Authors: Fineran Brian A. , Fineran Judith M.
Published: September 2008

A correlated thin-sectioning and freeze–fracturing approach was used to reveal the ultrastructure of endogenously dormant teliospores in the smut fungus Entorrhiza casparyana (Magn.) Lagerh. Conventional fixation and embedding methods yielded poor preservation of the wall and protoplasm. Successful preservation was achieved by fixing frozen and cryosectioned spores in glutaraldehyde and subsequently processing by standard procedures for transmission electron microscopy. Freeze–fracturing provided cross- and contour-fractured views of the protoplasm and the different layers of the wall. The wall is thick, consisting of three main layers: outer, middle, and inner, with the outer and inner layers further differentiated into zones. The warty zone dominates the outer layer and consists of radial protuberances (warts) with the regions between filled to varying degrees with similar wall material containing electron-transparent lamellae. The extent of differentiation of the warty zone is reflected in the surface morphology of the spores, which ranges from verrucose to almost smooth. At the base of the outer layer is an electron-translucent irregular zone. The middle and inner layers are regular in thickness around the spore, with the middle layer being the most electron dense. The inner layer is differentiated into three zones. The most distinctive is zone 2 which in freeze–fractured walls has an unique mosaic of striae. Cytochemical staining of the wall for polysaccharide material gives a positive reaction only for the warty zone. The protoplasm contains a single nucleus and is dominated by numerous spheroidal storage lipid bodies. Squeezed among the lipid bodies are organelles, believed to be microbodies, containing a granular matrix and often electron-transparent areas. These organelles failed to show catalase activity with the 3,3′-diaminobenzidine method. Occasional short profiles of endoplasmic reticulum cisternae, a few mitochondria with sparse cristae, dispersed small clusters of glycogen, and sometimes scattered ribosomes are also present in the cytoplasm. All these features are typical of dormant spores with a low metabolic activity.
Lignin and holocellulose relations during long-term decomposition of some forest litters. Long-term decomposition in a Scots pine forest. IV
Authors: Berg Bjorn , Ekbohm Gunnar , McClaugherty Charles
Published: September 2008

We investigated the relative changes in celluloses and lignin during decomposition of leaf and needle litters and wood in field experiments. The litter came from two different forest systems: one in the United States and one in Sweden. We found that the fraction of holocellulose in the total lignocellulose (Q) during decomposition approached an asymptotic value at which the disappearance of both the chemical components proceeded at the same rate. Different litter types approached different asymptotic values of Q. Possible implications of the finding are discussed.
Initiation and structure of the secondary vascular system in Phytolacca dioica (Phytolaccaceae)
Authors: Kirchoff Bruce K. , Fahn Abraham
Published: September 2008

Phytolacca dioica (L.) is characterized by anomalous secondary thickening by means of supernumerary cambia. After a period of primary growth and the formation of an initial (normal) vascular cambium, supernumerary cambia are initiated outside of the primary vascular cylinder. The initiation of the first supernumerary cambium takes place through approximately the number of nodes equal to the denominator of the phyllotactic fraction characterizing a given axis. At each node a segment of supernumerary cambium is initiated opposite the leaf traces supplying the leaf inserted at that node. The segments of differentiated cambium are preceded by regions of obliquely and anticlinally dividing cells. In the single juvenile axis studied supernumerary cambial segments also appear above the node to the cathodic side of the entering leaf traces, and opposite the medullary bundle immediately anodic to these traces. Vascular connections among the primary and supernumerary vascular cylinders occur between leaf insertions on the same orthostichy. The levels at which these connections occur vary among stems. The switch from ordinary to anomalous secondary growth may be caused by a change in tissue response to stimuli produced by leaves.
Effet du phosphate et du calcium sur la croissance et l'accumulation ionique chez les champignons ectomycorhiziens en culture in vitro
Authors: Mousain Daniel , Salsac Louis
Published: September 2008

The orthophosphate and calcium influence on growth and ionic accumulation was studied in several ectomycorrhizal fungi (Pisolithus tinctorius included) grown in vitro. The "optimal" growth was obtained with [Formula: see text] concentrations much lower than those of usual media: it may be represented by an exponential function, the parameters ("maximal" growth and "concentration of half-maximal growth") of which were calculated. For low phosphate and calcium concentrations in the medium the dry matter mass of the mycelium and their content of the two elements increased simultaneously. For high concentrations, an accumulation independant of growth was observed in the thalli. When the P. tinctorius mycelium accumulated phosphate and calcium in relatively large amounts, these accumulations seemed to be not correlated. Rather, the correlation between the accumulation of total phosphorus and that of potassium was significant. The ratio of acid-soluble P to total P decreased in the mycelium when the orthophosphate concentration increased in the medium.
Visualisation des centres générateurs selon la théorie phyllotaxique de Plantefol, dans le point végétatif du grand frêne (Fraxinus excelsior)
Authors: Cottignies Alain
Published: September 2008

To visualize the generative center of each foliar helix and its oriented progression, cell proliferation was studied in the ash (Fraxinus excelsior L.) shoot apex. The distribution of mitosis was analysed first with the hypothesis of the multiple foliar helices phyllotactic theory and then without any preliminary hypothesis. The cell cycles were asynchronic and mitotic duration was constant. Therefore, the parameters of both the Poisson distribution of mitosis in each apical zone and of mitotic density, evaluated by the nearest-neighbour method or by the rotation of a unit area, were indicative of the cell proliferation level. The axial zone differed from the initiating ring by virtue of its lower mitotic activity. The initiating ring was heterogeneous and involved two parts which were opposite each other and symmetrical with regard to the axis of the apex. In each half, the cell proliferation increased gradually to a generative center with a maximal mitotic activity, then decreased twice as fast. This heterogeneity showed the necessary rotation of a privileged mitotic wave, which progressed step by step in a single direction. The cartography of the cell proliferation intensity was mapped for one sample meristcm.
Acid-buffering capacity of foliage from boreal forest species
Authors: Pylypec B. , Redmann R. E.
Published: September 2008

Buffering capacity to acidity was defined as the microequivalents of H+ required to produce a 5 μeqiv. change of H+ concentration in a homogenate prepared from leaf tissue. The results for six species collected from the southern boreal forest of Saskatchewan, Canada, showed that trembling aspen (Populus trenudoides Michx.) and Labrador tea (Ledum groenlandicum Oeder.), had the highest buffering capacities (379 and 189 μeuiv. H+ ∙ g−1, respectively), while jack pine (Pinus banksiana Lamb.) had the lowest (33 μequiv. H+ ∙ g−1). Tamarack (Larix laricina (Du Roi) K. Koch), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) had intermediate values. Buffering capacity and pH of homogenates for all species showed seasonal fluctuations, with the lowest values occurring in the middle of the growing season. The results suggest that foliage of evergreen conifers, particularly jack pine, is less well buffered against acidic pollution than that of broad-leaved species such as trembling aspen.
Autofluorescence of vesicles, arbuscules, and intercellular hyphae of a vesicular–arbuscular fungus in leek (Allium porrum) roots
Authors: Jabaji-Hare S. H. , Perumalla C. J. , Kendrick W. B.
Published: September 2008

Vesicles, arbuscules, and hyphae of a species of Glomus in Allium porrum mycorrhizae autofluoresccd under four different ranges of wavelengths. Autofluorescence persisted when transverse sections were cleared in either 10% KOH or 1% NaOH and was intensified by staining the sections with Chelidonium majus L. root extract. The fluorescing component in the walls of the vesicular–arbuscular mycorrhizal structures was tentatively identified by spectrofluorometry as chitin.
The effect of glucose concentration and light on thallospore ultrastructure in Ellisomyces anomalus (Thamnidiaceae, Mucorales)
Authors: Beakes Gordon W. , Campos-Takaki Galba M. , Takaki Massonori
Published: September 2008

The development of chains of thallospores in the mucoraceous fungus Ellisomyces anomalus has been examined using scanning, thin section, and freeze-fracture electron microscopical techniques. The development and cytology of spores formed on high-glucose (HG, 4.0%) and low-glucose (LG, 0.06%) media, under both light and dark conditions, have been compared. The vegetative hyphae of spores on LG media accumulate glycogen particles in their cytoplasm but contain very little lipid. The cytoplasm of HG hyphae is packed with lipid globules. The thallospores are delimited by septa, which as in most other mucoraceous fungi are perforated by plasmodesmatalike pit connections. A thick secondary (spore) wall layer is accreted as the spores swell. Although mature thallospores on LG and HG media are similar in their external morphology, they show internal differences. HG spores are thicker walled and contain abundant lipid and glycogen reserves. LG spores contain relatively little lipid and are more highly vacuolate. The only structural differences observed between the carotene-rich, light-grown spores and their dark-grown counterparts is an increase in lipid globule electron density and an overall enhancement of membrane staining properties. The mature thallospores secede from the parent hyphae by both shizolytic (septum splitting) and rhexolytic (circumcissile hyphal splitting) mechanisms. From a developmental standpoint it is suggested the thallospores of Ellisomyces resemble thallic arthric conidia (arthrospores), simiar to those produced by Mucor rouxii, more closely than true chlamydospores, such as those produced by Gilbertella persicaria and Mucor mucedo.
Canadian and some extralimital Nodulosphaeria and Entodesmium species
Authors: Shoemaker R. A.
Published: September 2008

Twenty-eight species are illustrated and described from Canada or extralimital regions and keys to species are provided. One new species, N. revelstokensis, is described on Castilleja miniata Dougl. Twelve species are excluded.
Comparison of dendrograms: a multivariate approach
Authors: Podani J. , Dickinson T. A.
Published: September 2008

Three new descriptors of dendrogram structure (cluster membership divergence, subtree membership divergence, and partition membership divergence) have been proposed which supplement existing ones (cophenetic difference and topological difference). These enable multivariate comparisons among dendrograms in a manner that minimizes the drawbacks of individual descriptors and emphasizes their agreement. The new descriptors arc illustrated and compared with the existing ones by reference to an artificial data set. The multivariate comparison of dendrograms is further illustrated using two real data sets, one phenetic and one cladistic. These applications demonstrate the ability of this approach to reveal features of dendrograms that may be data dependent, method dependent, or due to the interaction of data and method, and that may not be readily apparent otherwise.
Hyphal extension and branch initiation in Polyporus arcularius: a biolaser microsurgical investigation
Authors: Valla G.
Published: September 2008

Procedures using a ruby biolaser to carry out microsurgical operations on growing hyphae are described. This method can be used to separate, destroy, or alter hyphal compartments without the necessity of transferring cultures. Separation of an apical compartment from its adjacent intercalary compartments was accompanied by a sudden but brief decrease in its elongation rate. Subsequently the previous extension rate of the hypha was reestablished. The duplication cycle in the apical compartment was not modified by the separation. Destruction of the apical compartment produced no detectable effect on the intercalary compartments. Treatment of hyphal tips induced a severe and permanent decrease in hyphal elongation and this was associated with the initiation of branches from the previously unbranched apical compartment. Treatment of the tip of a branched apical compartment did not have any persistent effect on the growth of its branches.
Structure et ontogenèse des néoformations observées in vitro sur le pétale de Begonia × elatior
Authors: Margara Jacques , Phelouzat Renée
Published: September 2008

On media containing a cytokinin and an auxin, petal explants of Begonia × elatior roots, produce in vitro leaves, and petaloid structures. When the auxin is 10−5 M, 2,4-dichlorophenoxyacetic acid, the organogenesis is temporarily inhibited. After subculture on a medium without auxin, neoformation of abnormal or atypical structures in then observed. All the structures originate from epidermal cells except the roots which arise from deeper parenchymatous cells. Numerous embryoids are observed. They can be normal or atypical. The acceleration of development of floral structures (progenesis) is illustrated by the formation of petaloid structures which can arise from floral meristems. Bipolar embryoids can have a root pole and a floral pole. Besides neoformation of normal bud meristems. the production of isolated leaves or petals is frequently observed. Generally, the external cells of neoformations accumulate anthocyan pigments or tannins in their vacuoles, making the histological study difficult.
Histopathology of canker development on peach trees after inoculation with Cytospora leucostoma
Authors: Wisniewski M. , Bogle A. Linn , Wilson C. L.
Published: September 2008

Anatomical changes in response to wounding or wounding plus inoculation with C. leucostoma were monitored over an 11-month period. Distinct bands of gum ducts in the xylem formed a barrier zone in all samples. Necrophylactic periderm (NP) formed at a faster rate in noninoculated samples. NP in inoculated samples was poorly delimited and weakly suberized in the callus tissue. Within 4 weeks after wounding, barriers in bark and xylem of inoculated samples were penetrated by wedges of mycelia. Callus in inoculated samples differentiated slowly compared with callus development in control wounds and multiple attempts to limit infection were ineffective. The effectiveness and value of a strong gumming response in reaction to Cytospora are discussed.
Temperature and light effects on the growth of Potamogeton crispus in Collins Lake, New York State
Authors: Tobiessen Peter , Snow Phillip D.
Published: September 2008

Potamogeton crispus, the curly leaved pondweed, was found to grow at low temperatures and very low light intensities: less than 1% of the surface irradiance. In both laboratory and lake studies, lower light intensities produced taller plants with fewer stems per propagule than plants grown at higher light intensities. Such a growth pattern may allow P. crispus to exist in deeper or less transparent water than other aquatic plants. Rapid growth in the early spring apparently permits P. crispus to become dominant while other possible competitors are still dormant.
Gametophytes of Botrychium lunarioides and their mucilage-coated rhizoids
Authors: Whittier Dean. P. , Peterson R. L.
Published: September 2008

Gametophytes of Botrychium lunarioides grown in axenic culture are thickened, white, dorsiventral structures with antheridia and archegonia on the dorsal surface. The antheridia are on a raised median antheridial ridge and the archegonia form on the steep flanks of this ridge. Rhizoids, unicellular and bicellular, arise on the marginal and ventral surfaces of the gametophytes. Multicellular rhizoids are initiated on the antheridia. All rhizoids have a transparent mucilaginous sheath which may be of uniform diameter or beaded. Histochemical studies have shown the mucilage to be composed of an acid mucopolysaccharide with polyphenolic materials present. It is proposed that the rhizoid mucilage functions like the mucilage on the roots of seed plants.
Cellular adjustments in the vascular cambium leading to spiral grain formation in conifers
Authors: Savidge R. A. , Farrar J. L.
Published: September 2008

Radial files of tracheids having changing orientations were traced through serial tangential sections to deduce events in fusiform cambial cells (FCCs) associated with spiral grain formation. Within an induction bridge of phloem and cambium sloping diagonally across a stem girdle in Pinus contorta Dougl. ssp. latifolia, repetitive, homologously sloping, pseudo-transverse anticlinal divisions in FCCs were a primary event contributing to FCC orientation changes. Imperfect periclinal divisions (IPDs) in FCCs also contributed. In Picea glauca (Moench.) Voss, IPDs and FCC elongation interacted to change tracheid orientation during natural spiral grain development. In both natural and induced reorientations, small numbers of adjoining FCCs changed their orientation abruptly while the greater population of FCCs changed orientation less rapidly. These sites of abrupt reorientation are termed "microdomains."not available
Decomposition of needle litter and its organic chemical components: theory and field experiments. Long-term decomposition in a Scots pine forest. III
Authors: Berg Björn , Ågren Göran I.
Published: September 2008

Scots pine needles were collected and field incubations were begun in the autumn of 6 consecutive years. The incubated needles were sampled three times a year and analysed for mass loss and chemical composition. The longest incubation time obtained was 1825 days. Four series of needles from a nutrition experiment (three levels of nutrient application and one control) sampled at one occasion were followed in the same way for 1448 days. The logarithm of remaining mass versus time of the pooled samples fits a linear regression well (average rate constant = 0.286 year−1, r2 = 0.963, n = 75). A higher resolution shows, however, that the decay rate decreases with time as the chemical composition changes. To better understand the decomposition process we have formulated a mathematical model for the course of mass loss as a system consisting of two fractions, a readily decomposable (labile) one and a refractory one. The mass loss from the two fractions can be direct or mass can be transferred from the refractory to the labile fraction. The model allows us to calculate the variation of the refractory fraction with time (generally there will always be some labile material in the system) and the decrease of the decomposition rate as a function of time or as a function of the concentration of the refractory fraction. We have found it possible to identify the refractory fraction both as the lignin fraction and as the nonsoluble fraction of the needles. The first identification yields a long transient response, whereas the second gives a system rapidly reaching a steady state. In both cases, the decay of the refractory material results in transfer of material to the labile fraction.
Probing secondary metabolism in plant cell cultures
Authors: Ellis B. E.
Published: September 2008

In vitro cultured plant cells which still express parts of their secondary metabolism phenotype are versatile experimental systems for studies of biosynthesis and metabolic integration, enzymology, and genome organization. Single cell manipulation can also provide insight into the question of cell-to-cell variability and metabolic competence.
The biochemistry and regulation of senescence in chloroplasts
Authors: Woolhouse Harold W.
Published: September 2008

The biochemical events in chloroplast breakdown are described. Special attention is given to the regulation of RNA, lipid, chlorophyll, and protein degradation. A new hypothesis is presented concerning the relationship between proteolysis and the initial steps in chlorophyll breakdown. It is argued that the dismantling of the chloroplast is a highly organized process and that the concept of loss of chloroplasts by digestion in a lytic vacuole is not tenable.
Interaction of cytokinins with lipid-associated oxy free radicals during senescence: a prospective mode of cytokinin action
Authors: Leshem Ya'acov Y.
Published: September 2008

In senescence physiology, experimental data indicate causative relationships among cytokinin, lipoxygenation, anti-oxidation, and lipid-associated free radical scavenging. During both normal and induced senescence, there is a rise in lipoxygenase (LOX) which catalyzes the oxidation of polyunsaturated fatty acids containing the cis, cis-1,4-pentadiene configuration. These include linoleic and linolenic acids, which are of common occurrence in plants and inter alia may be situated in membranal phospholipids. Lipoxygenation causes the production of free radicals such as the superoxide, fatty acid, and peroxy species. Cytokinin (CK) lowers LOX and superoxide dismutase activities significantly in senescing foliage and is mimicked by the endogenous lipid antioxidant, α-tocopherol (vitamin E), in its chlorophyll-retaining and LOX-lowering effects. Further experimentation indicated that CK interaction with free radicals may occur in two ways, (i) CK may act as a direct free radical scavenger by virtue of the fact that the hydrogens of the α-carbon atom in the amine bond can be extracted, resulting in the formation of an amide: [Formula: see text][Formula: see text] (this mechanism may also, in part, explain polyamine effects), (ii) CK may serve as an incipient preventative of free radical formation by inhibiting oxidation of plant purine compounds, which at certain stages of breakdown release superoxide and hydroxyl free radicals. This effect is probably associated with a lowering of substrate affinity for xanthine oxidase. This assumption is further borne out by similar senescence-retarding effects of selective xanthine oxidase inhibitors such as allopurinol. These observations collectively indicate that prevention of free radical formation and (or) their direct scavenging should be included in the multifactorial antisencscence mode of action of cytokinin.
Respiration, ethylene, senescence, and homeostasis in an integrated view of postharvest life
Authors: Romani Roger J.
Published: September 2008

The postharvest life of fruit is characterized by several well-studied, well-described physiological events and transitions. Principal among these are the respiratory and ethylene climacterics whose role(s) in postharvest life remain unresolved. Proposed is an integrative scheme based on the following assumptions: (i) Senescence is the overriding biological phenomenon of which ripening is a part. (ii) The energy demands of ripening are not sufficient to require a large respiratory increase. (iii) Irrespective of its specific mode of action, the general response of fruit to ethylene resembles, and presumably is, a stress response. (iv) Fruit cells are homeostatic and homeostasis is the countervailing trend to the stresses of senescence and ethylene. (v) Respiration, centered in the quasiautonomous mitochondria, is a measure of their homeostatic potential. The respiratory climacteric is seen as largely a mitochondrial homeostatic response to compensate for the degradative effects of incipient, programmed, cellular senescence. In turn, senescence is "fueled" by autocatalytic ethylene production which is an additive stress. The sequence of events begins when the response threshold is lowered to the level of endogenous ethylene by postmaturation, senescence-dependent increases in tissue sensitivity. Evidence and arguments, borrowed, adapted, or new, are presented in defense of this integrative view.
Microdistribution des espèces végétales sur des affleurements rocheux de dolomie, dans une érablière du sud du Québec
Authors: Cloutier André
Published: September 2008

The vegetation of dolomitic outcrops was sampled in a maple forest of southern Quebec. Multivariate analyses have demonstrated the influence of rockiness and size of outcrop on the distribution of herbaceous and woody plants. These results allow the description of five microcommunities. The flora of small cracks and hollows is exclusively herbaceous and of low diversity. Deeper soils support tree seedlings and saplings (mostly Acer saccharum) and also a diversified herbaceous stratum. The chemistry and mictotopography of outcrops produce mesic soils, rich in organic matter and nutrients. Soil depth segregates among plant species according to the size of their roots. Big outcrops have a more favorable microclimate. Dolomitic outcrops found in maple forests are biogeochemically rich microhabitats, which may support a more varied and abundant vegetation than does the surrounding forest floor. Primary succession on these outcrops is briefly discussed.
Trends and interrelationships in boreal wetland vegetation
Authors: Kenkel N. C.
Published: September 2008

Multivariate statistical methods were used to examine trends and interrelationships in 132 wetland stands at the southern edge of the boreal forest near Elk Lake, Ont., Canada. A total of nine vegetation types and seven species groups were recognized using cluster analysis. Nonmetric multidimensional scaling ordination of the stands indicated the underlying importance of nutrient status to the development of trends in vegetational variation. However, other factors such as the nature of the substratum, degree and periodicity of flooding, drainage, and water table level also appeared to be important. Analysis of the correspondence between vegetation types and species ecological groups indicated a trend toward the development of one-to-one relationships, suggesting that boreal wetlands may best be described as a series of relatively discrete communities. It is also suggested that species indicator values may be useful in characterizing boreal wetland stands.
A comparative study of initiation and development of embryogenic callus from haploid embryos of several barley cultivars. I. Developmental state of embryo explants and callus potential
Authors: Kott L. S. , Kott E. , Howarth M. , Kasha K. J.
Published: September 2008

Six cultivars of barley (‘Akka’, ‘Bruce’, ‘Klages’, ‘Leger’, ‘Perth’, and ‘York’) were compared for their ability to produce haploid embryos competent to produce embryogenic haploid callus. The capacity to generate such callus from scutellar epidermal cells is different among these cultivars and appears to be correlated with the developmental state–age of the embryo and associated with a rapid growth period. Histological examination of 12-, 14-, and 16-day-old embryos confirmed the meristematic nature of the callus-initiating cells and produced results which correspond well with results obtained from cultures of other similar embryos. Variability among cultivars in embryo development, root initiation from callus, and primary and secondary shoot regeneration was also identified.
In vitro propagation of Crambe maritima
Authors: Peron J. Y. , Regnier E.
Published: September 2008

A method for rapid micropropagation of sea kale (Crambe maritima L.) was developed. Petiole explants placed in vitro on a medium containing 0.5 mg/L indoleacetic acid (IAA), 6.0 mg/L kinetin, and 1.5 mg/L benzylaminopurine developed callus within 15 days and shoots within 28 days. Nearly four adventitious shoots could be developed within 3 weeks by placing the initial shoot on media without IAA. To develop roots, the shoots were then transferred to the basal medium containing 0.1 to 1.0 mg/L indolbutyric or α-naphthaleneacetic acid. Rooted plantlets were obtained within 2 or 3 weeks. After an acclimatization period of 6 weeks in a greenhouse in unsterilized medium, the plantlets could be set outdoors.