bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of seedling density on disturbed ground: role of seedling establishment for some midsuccessional, old-field species
Authors: Reader R. J. , Buck J.
Published: December 2007

In midsuccessional old fields, seedlings are often concentrated in patches of disturbed ground, such as earth mounds created by burrowing mammals. An experiment was conducted to determine whether interspecific variation in seedling density on mounds reflected interspecific variation in potential seedling establishment (i.e., the number of seedlings established per 1000 seeds sown). Seeds of 13 old-field forbs were sown on experimentally created mounds in an abandoned pasture. Their potential seedling establishment ranged from 0 to 156 seedlings per 1000 seeds sown, and seedling establishment was directly related to seed mass. The number of seedlings becoming established naturally on mounds ranged from 0.1 to 41 seedlings per mound for the 13 species. Natural seedling establishment and potential seedling establishment were not directly related. Instead, natural seedling establishment on mounds was correlated with species' frequency of occurrence off mounds. This suggests that seed availability may be more important than seedling establishment in controlling seedling density on mounds. However, if seed availability is unlimited or equal among species, then seedling establishment could control seedling density on disturbed ground. Key words: disturbance, seedling density, old field.
Composition and function of pyrenoids: cytochemical and immunocytochemical approaches
Authors: McKay R. Michael L. , Gibbs Sarah P.
Published: December 2007

At present, little physiological or biochemical data exist for pyrenoids mainly because isolation of intact pyrenoids using standard cell-fractionation methodology has met with only limited success. Techniques of microscopical cytochemistry and immunocytochemistry, however, readily lend themselves to the in situ investigation of pyrenoid composition. Immunocytochemical analyses have demonstrated that in evolutionarily diverse groups of pyrenoid-containing algae and hornworts, the Calvin cycle enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) is predominantly pyrenoid-localized. Moreover, the localization of Rubisco activase to pyrenoids of green algae and hornworts indicates that pyrenoid-localized Rubisco is catalytically competent. Although pyrenoids are reported to contain polypeptides other than Rubisco and Rubisco activase, none have been identified with certainty. The exclusion of phosphoribulokinase from the pyrenoids of red and green algae indicates that pyrenoids do not possess the full complement of Calvin cycle enzymes. There have been reports that nitrate reductase is pyrenoid-localized in green algae; however, this remains a contentious issue. Why Rubisco is localized to the pyrenoid is not clear. Available evidence does not support the extension to pyrenoids of a model recently devised for cyanobacterial carboxysomes in which the carboxysome is identified as an integral component of the inorganic carbon concentrating mechanism. Instead, perhaps the pyrenoid represents an evolutionary intermediate between cyanobacterial carboxysomes and the condition in which Rubisco is distributed throughout the chloroplast stroma. Key words: algae, hornworts, immunocytochemistry, chloroplast, pyrenoid, Rubisco.
Peptide composition and enzyme activities of isolated pyrenoids from the green alga Bryopsis maxima
Authors: Okada M. , Okabe Y. , Kono M. , Nakayama K. , Satoh H.
Published: December 2007

Pyrenoids of Bryopsis maxima contained several minor components other than the large subunit (LS) and the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). Among the minor components, polypeptides of 95, 67, and 41 kDa reacted with an antibody against the LS polypeptide. Amino acid sequences of these polypeptides were determined and compared with that deduced from the LS gene (rbcL) screened from the chloroplast DNA library of B. maxima. The N-terminal sequence of the LS peptide was not post-translationally processed and was almost identical with those of the polypeptides of 91, 67, and 41 kDa. The starch grains surrounding the pyrenoids contained a polypeptide of 66 kDa that was assigned as starch synthase. Key words: Bryopsis maxima, nitrate reductase, pyrenoid, rbcL, Rubisco, starch synthase.
Polypeptide composition and enzyme activities of the pyrenoid and its regulation by CO2 concentration in unicellular green algae
Authors: Kuchitsu Kazuyuki , Tsuzuki Mikio , Miyachi Shigetoh
Published: December 2007

Effects of environmental conditions on the pyrenoid were investigated in unicellular green algae. During adaptation to CO2 limitation, the pyrenoid and pyrenoid starch developed within several hours, while stroma starch was degraded, suggesting that metabolism around the pyrenoid is regulated independently from that in other stromal spaces. This pyrenoid development was light-dependent and inhibited by DCMU but was not affected by changes in nitrogen assimilation. Pyrenoids isolated from Chlamydomonas reinhardtii mainly consisted of the two subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), and several other polypeptides were detected. Phosphoribulokinase was not localized in the pyrenoid. Isolated chloroplasts were fractionated to separate intact pyrenoids from stroma and membranes. Rubisco activity was detected in both, and about 70% was distributed in the pyrenoid fraction in low-CO2 cells. The Rubisco content determined by SDS–PAGE, immunoblotting, and immunoelectron microscopy supported the above ratio. By fractionation of isolated chloroplasts under high ionic strength, a pyrenoid-like structure with high Rubisco activity was collected. It is suggested that the main carboxylation site in high-CO2 cells is the stroma, whereas Rubisco is concentrated in the pyrenoid and possibly functions in CO2 fixation under low-CO2 conditions. Key words: Chlamydomonas reinhardtii, chloroplast, CO2 concentration, photosynthetic CO2 fixation, pyrenoid, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco).
The acquisition of inorganic carbon by marine macroalgae
Authors: Johnston Andrew M.
Published: December 2007

Marine macroalgae inhabit three different environments: the eulittoral zone, rock pools, and the sublittoral zone. Many macroalgae exhibit C4 gas exchange characteristics, i.e., low CO2 compensation point, high pH compensation point, photosynthesis insensitive to changes in oxygen changes below 21 kPa, and a high affinity for inorganic carbon. It is concluded that in general eulittoral and rock-pool species are more C4-like than the subtidal species though there are interesting exceptions. Experimental evidence points to the following mechanisms being involved in inorganic carbon acquisition by macroalgae. The role of β-carboxylation as the primary step in carbon fixation is only convincing in Udotea flabellum, while PGA is the first product of 14C fixation in most species. Direct evidence of inorganic carbon accumulation is only available for Ulva fasciata, whereas Chondrus crispus does not have this ability. Studies show that carbonic anhydrase is prominent in the mechanism of carbon acquisition by Ascophyllum nodosum, and when inhibited the alga is dependent on CO2, whereas U. fasciata retains some ability to use bicarbonate ions. It is concluded that macroalgae display a range of inorganic carbon assimilation mechanisms that are active to varying degrees. The relationships between these mechanisms, the different macroalgal habitats, and carbonic anhydrase is discussed. Key words: inorganic carbon concentrating mechanisms, macroalgae, carbonic anhydrase.
Growth and resistance to herbivory in N2-fixing alders
Authors: Hendrickson O. Q. , Fogal W. H. , Burgess D.
Published: December 2007

Fixation of atmospheric N2 may provide an advantage to woody plants in N-limited environments, but may also alter their resistance to herbivory. Studies in adjacent plantings of three North American shrub alders (Alnus spp.) and three Eurasian tree alders showed significant species differences in susceptibility to a leaf-mining sawfly (Fenusa dohrnii) and in response to inoculation with a N2-fixing actinomycete (Frankia). During the first 5 years, woody biomass production ranged from 0.3 t∙ha−1∙year−1 in Alnus viridis ssp. sinuata (Sitka alder) to 8.3 t∙ha−1∙year−1 in Alnus incana ssp. incana (grey alder). Grey alder and another tree species (Alnus japonica) were attacked infrequently and suffered little sawfly damage except in plots with poor growth. The tree species Alnus glutinosa (black alder) was attacked frequently, and sawfly damage was greatest in plots with the best growth. The shrub species Alnus viridis ssp. crispa (green alder) was also attacked frequently but was highly resistant to larval feeding. Frequently attacked species showed greater damage in the lower portion of the crown. Frankia inoculation increased green alder biomass by 87% but had no significant effect on grey alder or black alder. The concept of a growth-defense trade-off does not fully explain the interactions between Alnus spp. and F. dohrnii. Key words: Alnus, Fenusa dohrnii, Frankia, biomass production, plant–herbivore interactions, leaf miner.
Patterns of growth and reproduction in a perennial tundra forb (Geum rossii): effects of clone area and neighborhood
Authors: Chambers Jeanne C.
Published: December 2007

The relationships of clone area and neighborhood to ramet size, reproductive effort, and spatial distribution within Geum rossii clones were studied in an alpine ecosystem on the Beartooth Plateau, Montana. Clones growing on an early seral site in relative isolation were compared to clones on a late seral site within dense, heterogeneous neighborhoods. Individual clones of G. rossii required a minimum clone area of about 200 cm2 before maximum ramet size and reproductive effort were achieved. Mean ramet size and reproductive effort were fairly constant among clones larger than 200 cm2 on both the early and later seral sites. Within clones the size and reproductive effort of ramets were positively related. Pattern analysis revealed that ramets became more widely and irregularly spaced as clone area increased on the early seral site. This may have been a geometric function of an increase in the space required as clones aged and became larger. On the late seral site, clones were characterized by ramets that were widely and erratically spaced, that had low leaf numbers and mass, and that had low reproductive effort. For clones of comparable area on the early seral site, ramets were more closely and uniformly spaced, and leaf number, mass, and reproduction per ramet were higher. Conservative patterns of growth and reproduction make G. rossii well suited to dominate in dense, heterogeneous neighborhoods of late seral sites and to colonize mineral soils of early seral sites. Similar to other clonal species, site characteristics and the type of neighborhood determine the trade-off between the physical occupation of space and the allocation to ramet growth and reproduction in G. rossii. Key words: Geum rossii, alpine, reproductive effort, growth, clone area, pattern analysis, succession, neighborhood.
Fire and drought experiments in northern wetlands: a climate change analogue
Authors: Hogenbirk John C. , Wein Ross W.
Published: December 2007

Drought and fire, which may increase in frequency and severity because of global warming, were simulated in mid-boreal wetlands by transplanting soil blocks upslope to a lower water table and by prescribed burns. In the 2 years after treatments were applied to seasonally flooded vegetation zones in the Peace–Athabasca Delta, Alberta, the drought treatment did not significantly change stem density and height of the dominant hygrophytes Calamagrostis canadensis and Carex atherodes. Dicotyledonous species' density and richness increased 3- to 36-fold on soil blocks moved upslope to the driest vegetation zone relative to unmoved soil blocks. The percent cover of native dicotyledonous species was unaffected but that of xerophytic Eurasian species, Sonchus arvensis and Cirsium arvense, increased 5- to 13-fold after drought treatment. Fire, particularly the deepest burn, reduced graminoid density and height up to 90%. Dicotyledon density, but not richness, was generally higher after fire. Plant cover was unaffected by fire but Eurasian species' cover was still 3- to 15-fold greater than that of native species. Seasonally flooded vegetation zones will likely be shifted from flood-driven dynamics with cool and moist environmental conditions towards drought- and fire-driven dynamics with warmer and drier conditions. It is hypothesized that, under these climate change conditions, Eurasian species might dominate early successional communities in mid-boreal wetlands. Key words: drought, fire, greenhouse effect, Peace–Athabasca Delta, wetland vegetation, Wood Buffalo National Park.
Leaf abscission kinetics of peach cultivars and clones in relation to peach canker disease
Authors: Biggs A. R.
Published: December 2007

Leaf abscission kinetics of several peach cultivars and clones were studied for 2 or 3 years at two locations. Cultivars varied significantly in leaf abscission rates, dates of 50 and 75% leaf abscission, and area under the abscission progress curve. ‘Veeglo’, ‘Madison’, and ‘Vivid’ exhibited the most rapid rates of leaf abscission, clone V68101 and ‘Redhaven’ showed moderate rates of leaf abscission, and ‘Babygold 5’, ‘Vanity’, ‘Candor’, ‘Earlired’, and clone V68051 were relatively slow to abscise leaves. No significant relationship could be demonstrated for any of the leaf abscission parameters with field performance ranks of cultivar susceptibility to the peach canker pathogens. Mean annual harvest date for the various cultivars or clones was not associated with susceptibility to the peach canker pathogens or any of the leaf abscission parameters. The role of autumn wound response in relation to screening for pathogen resistant peach genotypes is discussed. Key words: Prunus persica, Leucostoma spp., defoliation, resistance.
Barrier zone formation in host and nonhost trees inoculated with Ophiostoma ulmi. II. Ultrastructure
Authors: Rioux Danny , Ouellette G. B.
Published: December 2007

Barrier zone formation was studied in annual shoots and small branches of Ulmus americana L., Prunus pensylvanica L.f., and Populus balsamifera L. following inoculation with Ophiostoma ulmi (Buism.) Nannf. Ultrastructural observations showed that electron-opaque compounds, which usually were identified as containing phenolics by previous histochemical tests, were often present within cells of this tissue. Many lipidic globules were also observed within some barrier zone cells of Populus balsamifera. Additional wall layers, suberized or not, were frequently observed in these barrier zone cells. When histochemical tests for suberin at the light microscope level were strongly positive, the lamellation typical of suberin was evident in transmission electron microscopy. Gum canal formation in Prunus pensylvanica was found to be initiated and the canals widened predominantly by a lysogenous process. Key words: Dutch elm disease, nonhost plants, Ophiostoma ulmi, Ulmus americana, ultrastructure, gum canals, suberized layers.
Structure and development of Pinus banksiana – Wilcoxina ectendomycorrhizae
Authors: Scales Pamela F. , Peterson R. L.
Published: December 2007

Seedlings of Pinus banksiana were grown in growth pouches and inoculated with Wilcoxina mikolae var. mikolae, Wilcoxina mikolae var. tetraspora, and Wilcoxina rehmii. Ectendomycorrhizae formed between P. banksiana and W. mikolae var. mikolae developed rapidly following inoculation. The mantle was of variable width, and a large amount of mucigel was evident on the root surface. Intracellular penetration of the cortical cells by hyphae occurred one to two cells distal to Hartig net formation. Both light and transmission electron microscopy revealed labyrinthic growth of Hartig net hyphae that were densely cytoplasmic during early penetration stages but became vacuolate as the association aged. Intracellular colonization of the cortex was extensive, with the hyphae highly branched and surrounded by an interfacial matrix and cortical cell plasma membrane. The external morphology and anatomy of ectendomycorrhizae formed between W. mikolae var. tetraspora and W. rehmii and P. banksiana were similar to those described for W. mikolae var. mikolae. Key words: ectendomycorrhizae, Wilcoxina, Pinus banksiana, intracellular, Hartig net, E-strain.
Pedicel abscission of soybean: cytological and ultrastructural changes induced by auxin and ethephon
Authors: Oberholster S. D. , Peterson C. M. , Dute R. R.
Published: December 2007

Indole-3-acetic acid delayed the onset of pedicel abscission of soybean, Glycine max (L.) Merrill, by 20 h, and in some experiments, significantly reduced abscission over a 7-day treatment period. Cytological and ultrastructural development of the abscission zone could be divided into two phases: the first associated with longer cells and fewer multigrained amyloplasts in the incipient separation layer; the second with shorter cells (indicative of secondary cell division), increased numbers of amyloplasts, and significant changes in the percent volume of cytoplasm, vacuoles, and wall tissue. Middle lamella dissolution preceded cell separation. Indole-3-acetic acid delayed but did not disrupt the sequence of events leading to abscission. Ethephon treatment hastened abscission but both delayed and disrupted typical abscission events, especially secondary cell division, which occured less frequently. In addition, cellular collapse and greater swelling of cells were observed in the separation layer of ethephon-treated tissue. Key words: abscission, ethylene, Glycine max, indole-3-acetic acid, pedicel, raceme.
Répartition de la matière sèche entre les organes végétatifs et reproducteurs dans les pousses annuelles du hêtre européen (Fagus sylvatica)
Authors: Thiébaut B. , Comps B.
Published: December 2007

Resource allocations in plants can be estimated to study biomass distribution in the various organs during a vegetative cycle. Six isolated Europeen beech trees (Fagus sylvatica L.) of the same age were chosen within a station characterized by homogeneous ecological conditions: 229 annual shoots located on equivalent first order axes in the ramification were analysed to describe the distribution of dry material in leaves and stipules (for maintenance), in the axis (for present growth), in buds (for future growth), in infructescences (for female reproduction), and in male inflorescences (for male reproduction). The discrimination between acquisitions and allocations, which correspond to two different but complementary realities, is discussed. Development strategies are different between long and short vegetative shoots; the first one favours growth to explore the environment while the latter favours the maintenance to exploit it. When these two kinds of shoots flower and have additional resources, these new acquisitions are profitable both to vegetative and reproductive functions in short shoots, whereas a competition occurs between these functions in long shoots. Key words: resource allocations, dry material, annual shoots, European beech, Fagus sylvatica.
Chemical and morphological studies of the effects of ageing on monoterpene composition in Mentha ×piperita leaves
Authors: Brun N. , Colson M. , Perrin A. , Voirin B.
Published: December 2007

The effects of ageing on monoterpene composition in Mentha ×piperita have been studied by analyses of microsamples obtained by coupling a desorption–concentration–introduction technique with a gas chromatograph. The appearance and the development of the two types of glands of shoot meristem studied by scanning electron microscopy show that the capitate glands appear before the peltate glands. The chromatographic analyses of meristem and different primordial leaf pairs show that the monoterpenes are only detected if the leaf bears peltate glands and that the first cyclic compound accumulated is limonene. The biochemical variations of the reduction of menthone to menthol in the midstem leaves and of acetylation of menthol in the basal leaves start at the distal extremity of the leaf and progressively move towards the base. The maturation of the plant followed by the shift of the level of leaf in which menthone and menthol are present with the same percentage as a function of time is a linear phenomenon. Key words: peppermint, trichomes, monoterpenes, biochemical variations, ageing.
Evolution and differentiation of populations of Lotus corniculatus s.l. (Fabaceae) from the southern French Alps (Massif du Ventoux and Montagne de Lure)
Authors: Reynaud J. , Jay M. , Blaise S.
Published: December 2007

A chemical analysis of the polyphenolic patterns of diploid and tetraploid populations of Lotus corniculatus s.l. (Fabaceae) growing in the southern French Alps showed that diploids from Mont Ventoux and from Montagne de Lure belong to the same chemotype. On the other hand, tetraploids showed two different chemotypes. This paper suggests the following hypothesis about the evolution of Lotus corniculatus in this area since the last glaciation: diploids could be derived from a relic diploid population scattered by glaciation and restricted within very narrow areas, whereas the tetraploids originating from the diiploids were more competitive and radiated into larger areas cleared from ice. Key words: Lotus corniculatus, birdsfoot trefoil, Fabaceae, polyploidy, polyphenolic metabolism, evolution.
Bacterial dinitrogen fixation in the leaf of the northern pitcher plant (Sarracenia purpurea)
Authors: Prankevicius Andrew B. , Cameron Duncan M.
Published: December 2007

Bacterial (Azotobacteriaceae) nitrogenase activity in the leaf cavity of the insectivorous northern pitcher plant (Sarracenia purpurea L.) was assessed by acetylene reduction assay. Results indicated that bacterial dinitrogen fixation occurs in the leaf cavity under normal physiological conditions. This may represent a previously unidentified source of nitrogen for the pitcher plant, as the level of nitrogenase activity measured was sufficient to provide the plant with nitrogen well in excess of that required. Key words: pitcher plant, Sarracenia purpurea, dinitrogen fixation, Azotobacteriaceae, nitrogenase.
Electrophoretic evidence for the independent origins of two self-pollinating subspecies of Clarkia concinna (Onagraceae)
Authors: Allen G. A. , Gottlieb L. D. , Ford V. S.
Published: December 2007

Electrophoretic variation in 20 isozyme loci was examined in populations of Clarkia concinna, a spring-flowering annual plant native to the Coast Ranges of California. Clarkia concinna includes one outcrossing subspecies (ssp. concinna) and two allopatric self-pollinated subspecies (sspp. automixa and raichei). The two selfing subspecies contain different subsets of the alleles found in the outcrossing subspecies and possess few or no unique alleles (one rare allele in ssp. automixa, none in ssp. raichei). The two self-pollinated subspecies appear to have arisen independently from the outcrossing ssp. concinna. Key words: Clarkia, electrophoresis, isozymes, evolution of self-pollination.
The influence of cysteine, cysteine analogs, and other amino acids on spore germination of Alternaria species
Authors: Daigle Donald J. , Cotty Peter J.
Published: December 2007

The influence of amino acids on spore germination of Alternaria eassiae was investigated to develop a basis for improvement of mycoherbicide formulations. At a 1% concentration, the majority of amino acids exhibited little or no effect on spore germination in vitro. However, aspartic and glutamic acids stimulated germination, and serine, tryptophan, cysteine, and phenylalanine inhibited spore germination. Cysteine was the strongest inhibitor of germination and was active in the presence of potato dextrose broth, which is normally stimulatory. One percent cysteine reduced germination 96% after 4 h. Derivitization of the mercaptan or amino group but not the carboxylic acid group diminished the ability to inhibit spore germination. Cysteine also inhibited spore germination of Alternaria crassa and Alternaria macrospora. Application of cysteine reduced development of Alternaria leaf spot on cotton plants inoculated with A. macrospora. The results demonstrate diverse effects of amino acids on spore behavior and suggest cysteine or similar compounds may be useful in preventing diseases caused by Alternaria species. Key words: amino acids, biological control, cysteine, germination, potato dextrose broth, Alternaria leaf spot.
The Asterophoma anamorph of Chaenothecopsis savonica and its hyphomycetous synanamorph
Authors: Tibell Leif
Published: December 2007

A coelomycetous anamorph was obtained in axenic spore cultures of Chaenothecopsis savonica (Mycocaliciaceae, Cali-ciales). This anamorph is described. The anamorph has also been found on specimens collected in the field. A coelomycetous anamorph has not earlier been reported from Chaenothecopsis. The similarity between the anamorph of C. savonica and Asterophoma mazaediicola, a lichenicolous coelomycete occurring in the mazaedia of Calicium species, is striking. Asterophoma mazaediicola was grown from conidia, and conidiomata developed in culture. It is suggested that A. mazaediicola is the anamorph of a Chaenothecopsis species. In some cultures of C. savonica, a Phialophora-like hyphomycetous synanamorph developed. Key words: Mycocaliciaceae, Chaenothecopsis, Asterophoma, Phialophora, anamorphs, cultures.
Ultrastructure of conidia, conidium germination, and appressorium development in the plant pathogenic fungus Colletotrichum truncatum
Authors: Dyke C. Gerald Van , Mims Charles W.
Published: December 2007

Nongerminating conidia of Colletotrichum truncatum were coated with copious amounts of a finely fibrillar extracellular matrix. This matrix spread out onto the dialysis membrane used as a substrate in this study. Each thin-walled conidium contained a single nucleus that underwent mitosis 1–2 h following placement of aqueous suspensions of conidia on membranes. A septum subsequently developed near the middle of the conidium, creating two uninucleate cells. Just prior to or during septum development a germ tube emerged laterally, usually near one end of the conidium. The nucleus moved into the germ tube and underwent mitosis. One daughter nucleus remained in the germ tube, the other moved back into the conidium. Developing germ tubes appeared to produce large amounts of electron-dense, fibrillar material that coated their surfaces. This material blended into the remnants of the matrix initially coating conidia and could not be clearly differentiated from the latter material. Germ tubes grew to various lengths before forming appressoria. Appressorium differentiation began shortly after the germ-tube tip curved sharply. A septum developed to delimit the tip that differentiated into a swollen appressorium. By 6 h following initial hydration of conidia, appressoria were melanized and the surrounding extracellular material had condensed onto their surfaces, forming an electron-dense coating that appeared to stick appressoria to dialysis membranes. A tiny penetration peg developed from an apparently wall-less region on the underside of the mature appressorium and, in some instances, grew a short distance into the dialysis membrane. Key words: electron microscopy, freeze substitution, conidia, appressoria.
Competition and the response of three plant species to a salinity gradient
Authors: Kenkel N. C. , McIlraith A. L. , Burchill C. A. , Jones G.
Published: December 2007

Three grasses (Poa pratensis, Hordeum jubatum, and Puccinellia nuttalliana) were grown in monoculture and three-species mixture at each of eight salinity levels in a controlled environment chamber. In monoculture, all species grew best when no salts were added to the nutrient medium. When salts were added the species showed differing degrees of salt tolerance. Percent decreases in total biomass with increasing salinity and shifts in aboveground to belowground biomass ratios suggested increased salt tolerance in the order P. pratensis < H. jubatum < P. nuttalliana. In mixture, all species showed a significant change in salinity response when compared with their responses in monoculture. Interspecific competition resulted in P. pratensis being suppressed at all but the lowest salinities. Hordeum jubatum showed the least suppression at intermediate salinities, while P. nuttalliana was least suppressed at the highest salinities. These results indicate that interspecific competition results in a shift in the peak performance of more salt-tolerant species toward the high end of the salinity gradient. The species distributions in our experimental mixtures reflected those observed in the field, suggesting that competition plays an important role in structuring inland saline plant communities. Key words: halophyte, glycophyte, community, Hordeum jubatum, Puccinellia nuttalliana, Poa pratensis.
Protein bodies in Datura stramonium seeds: structure and mineral nutrient composition
Authors: Maldonado Sara , Lott John N. A.
Published: December 2007

The structure of protein bodies in the endosperm and embryo of Datura stramonium was studied with a variety of light-and electron-microscopic techniques. Protein bodies had one to several globoid crystals and one or two protein crystalloids in the proteinaceous matrix. Although the embryo protein bodies rarely had more than two globoid crystals, the endosperm protein bodies had varying sizes and numbers of globoid crystals, even within the same cell. Energy-dispersive X-ray analysis of globoid crystals revealed the presence of P, K, and Mg in all cases. Traces of Fe, Mn, and Zn were also found in globoid crystals of protein bodies from certain cell types. The distribution patterns of these three elements were quite specific; for example, Mn traces were found only in the globoid crystals of the protoderm. Neutron-activation analysis of endosperm and embryo tissues was used to quantitatively measure the concentration of Ca, Cl, Cu, I, K, Mg, Mn, Na, and S. The results from structural studies and the element analysis studies are discussed in the context of solanaceous seeds in particular but also with relation to seeds in general. Key words: protein bodies, Datura stramonium, seed, globoid crystals, energy-dispersive X-ray analysis, Solanaceae.
Initiation of appressorium formation in Uromyces appendiculatus: organization of the apex, and the responses involving microtubules and apical vesicles
Authors: Kwon Young H. , Hoch Harvey C. , Aist James R.
Published: December 2007

Urediospore germlings of Uromyces appendiculatus sense topographical signals inherent in host stomata over which they develop appressoria. The site of signal recognition by the fungus is invariably within the apical 6 μm of the germling. The organization of the germling apex before and during initiation of appressorium formation was examined by both electron microscopy and laser scanning confocal microscopy. Most notable were changes in the distribution and organization of the microtubules and apical vesicles. Microtubules were oriented parallel to the inductive ridge, along which expansion of the germling apex occurred. In germlings that contacted artificial inductive topographies in vitro, the distribution of apical vesicles in germlings did not change within the first 3–4 min. After 6–8 min of contact, most apical vesicles became repositioned near the ridge. The apical cluster in developing appressoria was closely associated with that population of cytoplasmic microtubules that developed parallel to the inductive ridge. Coincident with growth of the germling apex over an inductive ridge was a physical deformation of the cell by the ridge, indenting both the cell wall and plasma membrane. Key words: bean rust, cytoskeleton, infection structure, Spitzenkörper, urediospore.
Relationship between mycorrhizal activity, burning, and plant productivity in tallgrass prairie
Authors: Bentivenga S. P. , Hetrick B. A. D.
Published: December 2007

The impact of benomyl fungicide and spring burning on mycorrhizal activity and plant growth was assessed in tallgrass prairie in Kansas. We report for the first time that the productivity of mycotrophic plants can be reduced by inhibition of indigenous vesicular–arbuscular mycorrhizal fungi under field conditions. A vital stain, nitro blue tetrazolium, used to assess active mycorrhizal colonization, proved to be a more sensitive measure of treatment effects than the cell wall stain, trypan blue. Burning stimulated both plant growth and active mycorrhizal colonization. However, by 32 days after burning no differences in colonization were detected. Our observations support the hypothesis that mycorrhizal fungi play an important role in the growth of warm-season tallgrass prairie grasses and may contribute to enhanced plant growth of warm-season tallgrass prairie grasses and may contribute to enchanced plant growth following spring burning. Key words: burning, benomyl fungicide, phosphorus, tallgrass prairie, VA mycorrhizae, warm-season grasses.
Restriction enzyme mapping of the nuclear ribosomal cistron in selected Laminariales (Phaeophyta): a phylogenetic assessment
Authors: Saunders G. W. , Druehl L. D.
Published: December 2007

Restriction enzyme mapping of the nuclear ribosomal cistron was completed for a variety of Laminariales. Taxa investigated included Alaria marginata Postels and Ruprecht, Egregia menziesii (Turner) Areschoug, Eisenia arborea Areschoug, Lessoniopsis littoralis (Tilden) Reinke, Macrocystis integrifolia Bory, Nereocystis leutkeana (Mertens) Postels and Ruprecht, Postelsia palmaeformis Ruprecht, and Pterygophora californica Ruprecht, with Sargassum muticum (Yendo) Fensholt (Fucales) as an outgroup. The restriction maps establish a foundation for future phylogenetic, as well as other molecular, investigations in the kelp. We also assess restriction enzyme mapping of the nuclear ribosomal cistron for suitability in resolving intrafamilial and interfamilial taxonomic relationships in the Laminariales. The intergenic spacer proved too variable to be of use for phylogenetic comparisons at this level. Conversely, the gene regions were highly conserved, with only three restriction-site differences observed among all the laminarialean taxa investigated. Key words: Laminariales, rRNA, restriction enzyme mapping.
Uptake of arsenic by Aster tripolium in relation to rhizosphere oxidation
Authors: Otte M. L. , Dekkers I. M. J. , Rozema J. , Broekman R. A.
Published: December 2007

Arsenic present in salt marsh soil is taken up by plants and subsequently transferred to other parts of the ecosystem. The reduced state of the bulk soil of salt marshes favours the mobility of arsenic. In the rhizosphere of plants however, arsenic may be immobilized owing to oxidation of arsenic (III) to less mobile arsenic (V) and adsorption to iron (hydr-)oxides. In a field survey iron concentrations in the vicinity of roots of Aster tripolium were higher than in the bulk soil. In a greenhouse experiment accumulation of arsenic and iron in the rhizosphere occurred, which could be due to the oxidizing activity of plant roots and (or) microorganisms. This process stimulates uptake of arsenic by salt marsh plants. The formation of an iron plaque seems to play an important role in the uptake of arsenic by salt marsh plants, as was indicated by an incubation experiment with root parts of A. tripolium. The results of the experiments indicate that iron plays a key factor in determining the mobility of arsenic in salt marsh soils and in the uptake and translocation processes in the plants. Although oxidation processes in the rhizosphere enhance uptake of arsenic, it may be an important detoxification mechanism for the plants. Key words: arsenic, Aster tripolium, iron, rhizosphere, salt marsh.
New species of Amanita from Western Australia
Authors: Miller Jr. Orson K.
Published: December 2007

Eleven new species of Amanita, Amanitaceae, are described from the southern Eucalyptus-dominated forests of Western Australia. One distinctive species is referred to subgenus Amanita, section Amanita. The other 10 species are members of the subgenus Lepidella, 5 in section Lepidella, 2 in section Validae, and 3 in section Phalloidae. All 11 species were fruiting in native Eucalyptus forests from 247 km north of Perth to Albany, 424 km south of Perth, on the southern coast. Key words: Basidiomycetes, Amanitaceae, Amanita, Eucalyptus, Western Australia.
Electron microscopic and chemical study of degraded Pinus radiata wood from a marine pile
Authors: Singh A. P. , Hedley M. E.
Published: December 2007

During an inspection of marine piles, 12 years after installation, severe degradation was noted on one of them in the vicinity of a corroded eyebolt. The wood was dark brown in colour and tended to crumble easily. Wood fragments were examined by light microscopy and scanning and transmission electron microscopy and were also analyzed for carbohydrates and lignin. Light microscopy indicated numerous cracks in tracheid walls resulting in delamination at the middle lamella – S1 and S1–S2 boundaries and also in fractures across the tracheid wall. Chemical analysis showed extensive loss of both hemicellulose and cellulose. Observations with polarized light microscopy supported the data from chemical analysis on cellulose degradation, indicating a loss of crystallinity. Although presence of microbial flora in the lumen of wood cells was revealed by scanning electron microscopy, transmission electron microscopy showed only occasional soft rot decay zones in the S2 layer. The degradation of Pinus radiata wood from this sample appears to have been caused primarily by brown rot attack and (or) iron corrosion products, soft rot attack playing a minor role. Key words: Pinus radiata wood, marine pile, wood cell wall degradation, electron microscopy.
The phytogeography of rare vascular plants in Ontario and its bearing on plant conservation
Authors: Argus George W.
Published: December 2007

The phytogeographic patterns displayed by the 550 rare vascular plant taxa in Ontario, including 349 that are rare nationally, are correlated with counties, site regions, and floristic provinces. Rare taxa are concentrated in southwestern Ontario decreasing northward, with secondary concentrations along the Hudson Bay coast. Rare taxa in Ontario are predominantly peripheral taxa, which have their main ranges outside of Ontario. Many of these taxa, however, have a high Canadian conservation priority because they are also at risk in adjacent states or provinces. Rare taxa with Appalachian and Coastal Plain affinities are most common in southwestern Ontario. Arctic and boreal affinities predominate in Northern Ontario. These patterns are correlated with temperature and moisture parameters, which are incorporated with the Hills' site regions classification. Most high conservation priority taxa occur in the Carolinian region, the most highly settled and most highly agriculturalized part of the province. There is an urgent need for conservation of the remaining forest and wetlands in this region. The fragmentary ecosystems still remaining must be protected from further development. There is a need to study the correlation of rare plant occurrences with existing parks and reserves throughout the province to facilitate the identification of priority regions for protection. Key words: rare plants, phytogeography, conservation, Ontario.
Conspectus of the genus Douglasia (Primulaceae) with comments on Douglasia alaskana, an Alaska–Yukon alpine endemic
Authors: Kelso Sylvia
Published: December 2007

The endemic North American genus Douglasia has been considered dubiously distinct from its widespread Asiatic relative Androsace, differing primarily in flower color and growth habit. The distinctive nature of Douglasia is reaffirmed here, and the definition of the genus is amplified with additional characters that include an exserted corolla tube, stellate pubescence, multiple scapes, sessile umbels, and a higher chromosome number. A species endemic to Alaska and the Yukon, formerly known as Androsace alaskana, is transferred to Douglasia on this basis. This taxon is apparently closed related to Asiatic members of Androsace and may represent an ancestral link between the two genera. Key words: Androsace, Arctic, Douglasia, Primulaceae.
Ascospore ultrastructure of Pleospora gaudefroyi (Pleosporaceae, Loculoascomycetes, Ascomycotina)
Authors: Yusoff M. , Moss S. T. , Jones E. B. G.
Published: December 2007

Ascospore and spore appendage ultrastructure in Pleospora gaudefroyi is described. Ascospore walls comprise a three-layered mesosporium within which electron-dense bodies (melanin?) are deposited in two layers (W2, W3), a tripartite episporium (W4), and an outer mucilaginous sheath (exosporium?). The electron-dense inclusions in the mesosporium are compared with those in the conidia of Alternaria brassicicola and ascospores of Carbosphaerella leptosphaerioides. In the unitunicate marine Ascomycetes, ascospores with a sheath are uncommon, whereas in the Loculoascomycetes many species have such ascospores. The sheath in P. gaudefroyi is compared with those of Paraliomyces lentiferus, Massarina thalassiae, and Massarina armatispora (all Loculoascomycetes). Key words: appendage ontogeny, marine Ascomycotina, taxonomy, ultrastructure.
Potential role of fungi and bacteria in Chinese fir replant soil
Authors: Zhang Qishui , Zak John C.
Published: December 2007

The role of soil fungi and Bacillus in the Chinese fir (Cunninghamia lanceolata) replant problem was investigated. Several pathogenic fungi isolated were more abundant in replant than in non-replant woodland soil, but the species composition of soil bacteria showed no significant differences. Fumigation of replant soils with methyl bromide significantly increased the growth of Chinese fir compared with nonfumigated soils. Inoculation of steam-sterilized soil with the pathogenic fungi caused significant reduction of growth of Chinese fir seedlings, while amendment with bacteria from the soil had no effect on seedling growth. However, the combination of pathogenic fungi and bacteria greatly reduced plant growth and increased root rot compared with pathogenic fungi or bacteria alone. It is suggested that fungi alone or in combination with bacteria may be important biotic factors in the Chinese fir replant problem. Key words: fungi, bacteria, Chinese fir, replanted soil, seedling growth.
Genetic variation in central and disjunct populations of Lilium parryi
Authors: Linhart Yan B. , Premoli Andrea C.
Published: December 2007

We compared levels of genetic variability in small, isolated populations of Lilium parryi in Arizona with those found in large populations in California. Arizona populations were presumably derived from California populations; they were significantly less variable and showed evidence of much higher levels of inbreeding. One California locality whose population structure is similar to those found in Arizona also had relatively low levels of genetic variability. However, the other California populations were highly variable and showed lower levels of inbreeding than Arizona populations. There was significant genetic differentiation among all populations. In Arizona, there was no relationship between current population size and genetic variability. Arizona populations may be vulnerable to extinction, given the magnitude of environmental modifications in their habitats, their small sizes, and their low levels of variability. Key words: genetic structure, rare species, hawkmoth pollination, Lilium, disjunct populations.
Recovery of haploid plants from asparagus microspore culture
Authors: Feng X. R. , Wolyn D. J.
Published: December 2007

Asparagus (Asparagus officinalis L.) microspore culture was performed in an array of experiments that assessed the roles of plant growth and culture conditions. The following protocol provided the best results. Flowers with microspores at the late uninucleate stage of development were collected from greenhouse plants grown at 22:18 °C (light:dark) and stored at 5 °C for 3 days. One millilitre of MS medium plus 0.2 g/L yeast extract, 500 mg/L casein hydrolysate, 800 mg/L glutamine, 2.0 mg/L naphthaleneacetic acid, 1.0 mg/L benzyladenine, and 6% sucrose (MSFY) was conditioned with 10 anthers/mL for 1 week, after which it was filtered. One hundred anthers were added to shed their microspores (1.6 × 105 per mL) and were removed after 3 weeks when 0.5 mL of fresh medium was added. Cultures were incubated at 35 °C for 1 week, then 30 °C for 5 weeks. Microcalli were collected subsequently on a 100-μm screen and placed on induction medium (MSFY minus yeast extract, plus 3 g/L gelrite) in darkness at 35 °C for 4 weeks and then in light at 25 °C for 4 weeks. Shoots, roots, and bipolar embryos were produced. The latter were transferred to maturation medium (MS plus 0.1 mg/L naphthaleneacetic acid, 0.5 mg/L kinetin, 3% sucrose, 3 g/L gelrite, and 0.65 mg/L ancymidol) for 4 weeks, then to germination medium (MS plus 1.0 mg/L gibberellic acid, 3% sucrose, 3 mg/L gelrite). Plantlets were grown and maintained on maturation medium. Approximately 0.3% of the cultured microspores produced calli, and 85% of calli produced plantlets. Of 10 plants analyzed, 2 were haploid, 7 were diploid and, 1 was tetraploid. Key words: asparagus, haploid, microspore.
Effects of fertilization on growth and nutrient use by Chamaedaphne calyculata in a raised bog
Authors: Bartsch Ingrid
Published: December 2007

Biomass and flower production, shoot growth, and shoot N, P, and K concentrations of Chamaedaphne calyculata were determined in a bog in central Maine. Two separate field experiments were used to compare growth, reproductive output, and shoot nutrient contents of Chamaedaphne: (i) over two seasons under ambient conditions and following addition of N, P, and K individually and in combination; and (ii) during one season using a complete factorial design with three levels of both N and P. Biomass production and shoot length doubled following 1 year of N–P or N–P–K addition, whereas 2 consecutive years of addition tripled these characteristics. Growth responses were accompanied by an increase in tissue N, P, and K concentrations. The most striking response was a fivefold increase in the mass of flower buds produced per plant at the highest levels of N–P and N–P–K addition. The effects of N and P were interactive, and both the absolute quantity and ratio of N:P added were important in terms of the magnitude of the responses. Responses to N were typically curvilinear, whereas responses to P were both curvilinear and linear. Although Chamaedaphne is adapted to low levels of nutrient supply, it responds to the addition of nutrients by increasing the production of vegetative and reproductive tissue and by increasing the content of P in shoots. Without additional supplies of N, P, and K, growth by Chamaedaphne in bogs may be restricted by competition for nutrients with Sphagnum. Key words: Chamaedaphne, bog, nitrogen, phosphorus.