bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental study of floral display size and reproductive success in Viburnum opulus: importance of grouping
Authors: Krannitz Pam G. , Maun M. Anwar
Published: December 2007

Two components of the floral display of Viburnum opulus L. were manipulated to determine their effect on fruit initiation and maturation. We altered the size of the floral display by planting individual shrubs in groups of 1, 5, or 10 in 1985 and in groups of 2 or 6 in 1986. In addition, we changed inflorescence size by altering the number of sterile accessory flowers per inflorescence: 0, 4, or untreated in 1985 and 0 or untreated in 1986. The sterile-flower treatment did not explain a significant proportion of the variation in fruit initiation or maturation. In contrast, the plant-grouping treatment was significant in 1985 but not in 1986. The number and proportion of fruits initiated were higher in larger groups of plants than in small groups in 1985 (P < 0.0001 for analyses performed at group and plant levels). The proportion of fruits initiated in group sizes 1, 5, and 10 was 6.9, 15.0, and 22.7% per plant, respectively, and 4.3, 9.1, and 19.4% per inflorescence, respectively. The larger groups did not initiate or mature proportionally more fruits in 1986. Twice as much rain fell in 1986 as in 1985, and shrubs produced more fruits overall (32.2% fruit initiation versus 11% in 1985), but it is not clear why group size differences did not have an effect on fruit initiation and maturation in 1986. Within the plant-grouping treatment fruit initiation and maturation were always significantly correlated with flower number (P < 0.0001) in both 1985 and 1986, but the increase in the number of fruits initiated was not proportional to the increase in flower number. Key words: floral display size, fruit initiation, plant grouping, pollination, Viburum opulus.
A morphometric analysis of leaf development in Vitis riparia, and grape cultivars Concord and Vivant
Authors: Lacroix Christian R. , Posluszny Usher
Published: December 2007

This study investigates the initiation of leaf shape in three taxa of Vitis from a quantitative point of view. Leaf characters, such as angles between major veins, ratios of the length of leaf lobes, of leaf lobes and sinuses, and of petioles and leaf lobes, were measured on leaves of different sizes and compared against leaf blade length (an indirect measure of developmental time) to see if there were differences between them at different developmental stages, and between taxa. Two trends were observed. Characters dealing with angles between major leaf veins, and those dealing with the ratio of the distance to the first point of branching of the major leaf vein of a lobe and the length of that leaf lobe, showed relatively little change over leaf blade length compared to more variable characters such as those involving the leaf petiole, leaf sinuses, or leaf lobes. If we assume that leaves of different lengths represent leaves at different stages of development, we can say that the characters dealing with angles or venation do not change extensively over time. However, characters dealing with ratios of the distance to a leaf sinus and lobe length, ratios of the length of two leaf lobes, or those dealing with the ratio of the length of the petiole and lobe length showed a stronger indication of change over leaf blade length. The parameters of interest in most of these ratios (petiole length or sinus depth compared against the length of a leaf lobe) varied more at different leaf blade lengths. It was also possible to distinguish between taxa for characters dealing with leaf lobes, petioles, and sinuses. Key words: morphometry, leaves, Vitis, development, characters, shape.
Effect of simulated acid rain on the epicuticular wax of Scots pine needles under northerly conditions
Authors: Turunen Minna , Huttunen Satu
Published: December 2007

The long-term effects of simulated acid rain treatment (pH 4 and pH 3) on the physicochemical characteristics of the needle surfaces in a natural stand of Scots pine was investigated in the extreme north of Finland during the period 1985–1988. By the end of this period, the pH 3 treated pines had received a sulphur load of 7.48 g m−2 and a nitrogen load of 2.62 g m−2, and the pH 4 treated pines a sulphur load of 1.23 g m−2 and a nitrogen load of 0.43 g m−2 in addition to ambient deposition. No visible symptoms of acid rain injury were observed in the needles, but their growth was significantly reduced. Delayed development of the epistomatal waxes and four types of deformed stomatal complex, namely narrow, half-formed, occluded, and double-sized, were found by scanning electron microscopy. The total number of deformed stomatal complexes in the pH 4 treated pine needles was over 50% greater than in dry control specimens and over 70% greater than in water controls. The rapid erosion of young, undeveloped waxes increased needle wettability (11%) significantly, but the quantity of chloroform-soluble waxes had decreased only slightly. The effects of acid rain on the epicuticular waxes were accentuated during unfavourable growing seasons with reduced effective temperature sums. Key words: acid rain, Scots pine, epicuticular wax, wettability.
Quantitative genetics of disease incidence in Ustilago hordei controlled by virulence and aggressiveness genes
Authors: Pope David D. , Wehrhahn Conrad F.
Published: December 2007

Biometric analyses of variability in the disease incidence phenotype were performed using three F2 dikaryotic populations of the smut fungus Ustilago hordei (Pers.) Lagerh. on barley cultivars 'Trebi' (partially resistant) and 'Odessa' (universal suscept). The variance component involving interactions between segregating genes of U. hordei and environmental factors made the largest contribution towards the disease incidence on both cultivars. Additive and nonadditive (dominant and epistatic) gene effects contributed significantly to total disease incidence variation on both 'Trebi' and 'Odessa'. Heritability (additive genetic variance) was 2.5 times higher on 'Trebi' than on 'Odessa', and nonadditive variance effects were higher on 'Odessa' than on 'Trebi' by a factor of 1.5. Five effective factors were estimated to be segregating in the F2 populations; the virulence gene and four agressiveness factors. It is hypothesized that certain aggressiveness polygenes interact either with at least one other aggressiveness polygene or with the virulence gene. Analysis of variance–covariance provided supporting evidence for the epistatic activity of some genes and weak evidence for possible previous selection for intermediate optimal rather than maximal expression of the disease incidence phenotype. Key words: Ustilago hordei, aggressiveness, polygenes, disease incidence, smut.
Early embryogenesis in Arabidopsis thaliana. I. The mature embryo sac
Authors: Mansfield S. G. , Briarty L. G. , Erni S.
Published: December 2007

Arabidopsis thaliana has a seven-celled eight-nucleate megagametophyte of the Polygonum type; each cell type displays a different form of structural specialization. The egg apparatus cells are highly polarized; the egg has a large micropylar vacuole and chalazally sited nucleus, whereas the opposite is true for the synergids. At the chalazal region of the egg apparatus cells there are no cell wall boundaries, although their plasmalemmas are in intimate contact. The common wall between the two synergids is thin and irregular and contains plasmodesmatal connections. The synergid cytoplasm is rich in organelles; profiles of rough endoplasmic reticulum appear in masses of parallel stacked cisternae, and large accumulations of mitochondria occur adjacent to the filiform apparatus. The egg cell cytoplasm is quiescent; ribosome concentration and frequencies of dictyosomes and endoplasmic reticulum are noticeably lower and plastids are poorly differentiated. The central cell is long and vacuolate with a large diploid nucleus; fusion of the polar nuclei occurs prior to embryo sac maturity. The cytoplasm contains numerous starch-containing plastids accumulated in a shell around the nucleus. A high ribosome concentration and the absence of vacuoles and dictyosomes typifies the antipodal cell cytoplasm. All antipodal cells are interconnected by plasmodesmata as well as being connected to the nucellus and central cell. Key words: Arabidopsis, embryo sac, embryogenesis, cell specializations, stereology.
Early embryogenesis in Arabidopsis thaliana. II. The developing embryo
Authors: Mansfield S. G. , Briarty L. G.
Published: December 2007

Embryo differentiation in Arabidopsis thaliana follows the classical Capsella variation of the Onagrad type. Fertilization occurs approximately 3 h after flowering, whereupon vacuolar organization in the zygote changes and the cell elongates rapidly to approximately three times its original length. Cytoplasmic polarization is maintained. During the first two division steps there is very little increase in total cell volume, and during subsequent divisions vacuole number increases, with a concomitant decrease in size. Plastids remain undifferentiated up to the late globular stage, after which grana begin to develop. Ribosomal concentration increases significantly after fertilization. Differences between embryo proper cells become evident by the heart stage; vacuole, plastid, and mitochondrial abundance, size, and complexity vary within the embryo. There are no plasmodesmatal connections with the endosperm or integuments. Suspensor development is complete by the early globular stage, when it consists of seven to nine highly vacuolate cells, each linked by end wall plasmodesmata. Ribosome and volume densities of plastids and mitochondria are significantly lower than in the embryo proper organelles, and dictyosomes are infrequent. Embryo sac wall projections proliferate throughout the micropylar chamber, especially adjacent to the filiform apparatus and zygote base, and ingrowths form on the basal cell proximal wall. Key words: Arabidopsis, embryogenesis, embryo differentiation, wall ingrowths.
Psoralens on the surface of seeds of Rutaceae and fruits of Umbelliferae and Leguminosae
Authors: Zobel Alicja M. , Brown Stewart A.
Published: December 2007

Linear furanocoumarins (psoralens) were present both inside and on the surface of dry fruits of seven species of Umbelliferae and one species of the Leguminosae and on seeds of three of Rutaceae examined. Surface concentrations varied between traces and 40 μg/g of the mature fruits or seeds, amounting to 0.38–43% of the total. In the whole fruits concentrations were very high in Angelica archangelica, Heracleum lanatum, Pastinaca saliva, and Psoralea bituminosa, reaching levels of milligrams per gram fresh weight of fruits. This high concentration inside the fruit may be the cause of poor germination of embryos in A. archangelica and H. lanatum. Seeds of the Rutaceae had much smaller concentrations of furanocoumarins both on the surface and within the seed. Key words: fruits, seeds, surface, furanocoumarins, Umbelliferae, Rutaceae, dermatitis, plant defense.
A new genus, Rotiferophthora, to accommodate the Diheterospora-like endoparasites of rotifers
Authors: Barron G. L.
Published: December 2007

The species of Diheterospora attacking bdelloid rotifers have been compared with Diheterospora chlamydosporia and found to be different in a number of important characteristics. These include the consistent presence of aphanophialides, proliferation of phialides and aphanophialides to form polyphialides, containment of the conidial mass in a hydrophobic membrane, reduction or elimination of the verticillate arrangement of the conidiogenous cells, and presence of a large oil droplet in each conidium. It is considered that these differences are sufficient to separate the rotifer parasites from both Diheterospora and Verticillium. Accordingly, a new genus, Rotiferophthora, is erected to accommodate the 17 species recognized in this group of fungi. Thirteen rotifer parasites previously described under Diheterospora, Verticillium, or Acrostalagmus are transferred to Rotiferophthora, and four new species of Rotiferophthora are described. Key words: Diheterospora, Rotiferophthora, endoparasite, rotifer.
Biomass increase and associative nitrogen fixation of mycorrhizal Pinus contorta seedlings inoculated with a plant growth promoting Bacillus strain
Authors: Chanway C. P. , Holl F. B.
Published: December 2007

One-month-old Pinus contorta Dougl. seedlings were inoculated with mycorrhizal fungi (Wilcoxina mikolae isolate R947), plant growth promoting bacteria capable of fixing nitrogen (Bacillus strain L6), or coinoculated with a combination of Wilcoxina and Bacillus. Seedlings were grown with 0.35 mM Ca(15NO3)2 (5% 15N atom excess) as the only nitrogen source. Fungal inoculation alone resulted in the synthesis of ectendomycorrhizae but decreased shoot biomass. Bacterial inoculation alone did not affect seedling biomass or foliar nitrogen content. Coinoculation of seedlings with Wilcoxina and Bacillus resulted in a similar degree of ectendomycorrhizal infection compared with fungal inoculation alone, but shoot biomass was greater than that of seedlings receiving the fungus alone. Root biomass and stem height were not altered by coinoculation. Total foliar nitrogen was lower in seedlings inoculated with Wilcoxina, and coinoculation with Bacillus did not reverse this trend. Based on the 15N to 14N ratio of foliage, associative nitrogen fixation by Bacillus contributed 4% (P < 0.05) of seedling foliar nitrogen whether or not seedlings were mycorrhizal. However, coinoculated seedlings had lower foliar nitrogen (percentage basis) compared with uninoculated controls. These results suggest that growth of mycorrhizal pine can be stimulated by inoculating with beneficial bacteria. Growth promotion does not result from increased formation of ectendomycorrhizae and may, only in part, result from associative nitrogen fixation. Key words: Pinus, microorganisms, growth promotion, nitrogen fixation.
Characterization of red alder ectomycorrhizae: a preface to monitoring belowground ecological responses
Authors: Miller Steven L. , Koo C. D. , Molina Randy
Published: December 2007

Critical ecological research on belowground ecosystems has often been impeded because of the inability to adequately recognize ectomycorrhizal relationships, especially the abundance, diversity, and distribution of the fungus component, and the specificity of particular fungus–host combinations. Red alder, with its high degree of host specificity and paucity of fungal symbionts, provides an ideal model for studying these attributes. Eleven morphologically recognizable types of ectomycorrhizae were characterized from field-collected root material, greenhouse soil bioassays, and laboratory syntheses. Most mycobionts were basidiomycetes, as evidenced by abundant clamp connections present in the mantle and extramatrical hyphae. Seven mycobionts identified to species included Alpova diplophloeus, Thelephora terrestris, Lactarius obscuratus, Cortinarius bibulus, Laccaria laccata, Hebeloma crustuliniforme, and Paxillus involutus. Many of the ectomycorrhizae collected in the field appeared to have more than one mycobiont present in the mantle. Root tips could generally be categorized into either flexuous or succulent morphological types. The flexuous types were long, thin, indeterminate in growth, with an acute root apex, and the mantle and Hartig net in longitudinal section were not well formed near the root apex. The succulent types were short, thick, determinate in growth, with a rounded root apex, and the mantle and Hartig net in longitudinal section were well formed near the root apex. Additional characteristics important in distinguishing among red alder ectomycorrhizal types included color, extent of extramatrical hyphae development, mantle surface characteristics, and selected microchemical reactions. Mantle thickness was highly variable and not useful in characterization. Hartig net development was shallow, and regardless of mycorrhizal origin, rarely extended beyond one epidermal cell layer. Key words: ectomycorrhizae, Alnus, characterization, ecology, belowground.
Elemental dynamics in forested bogs in northern Minnesota
Authors: Grigal D. F.
Published: December 2007

Dynamics of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) were determined for three perched bogs, formed by lake filling, and three raised bogs, formed by landscape swamping. N and K concentrations were higher in the undergrowth of perched bogs, and Ca and Mg concentrations were higher in subsurface anaerobic peat of raised bogs. Elemental pools in vegetation were in the order N > Ca > K > Mg > P; in surface peat, N > Ca > Mg > P = K. Differences in elemental mass between the bog types were closely related to biomass differences. The atmosphere potentially supplied from 3% of annual plant uptake of K to 20% of Mg; this fraction was inversely related to uptake as a proportion of the surface peat. Vegetation on raised bogs had a greater proportion of uptake from the atmosphere (15 vs. 12%), a faster rate of elemental turnover (3.8 vs. 4.8 years), and lower net primary productivity (NPP) than on perched bogs, all indicative of a lower nutrient status. The annual mineralization rate of the surface peat for both bog types was estimated at 1.5% year−1; NPP predicted from N mineralized at this rate agrees well with observations. The better nutritional status of perched bogs may be related to landscape position, with potential inputs via runoff from adjacent uplands. The nutrient capital in both bog vegetation and substrate was similar to that in upland northern conifer forests. Key words: acrotelm, ombrotrophic, raised bogs, nutrients, peatlands, nutrient cycling.
Microsite- and age-specific processes controlling natural populations of Acer saccharum at cliff edges
Authors: Bartlett R. M. , Matthes-Sears U. , Larson D. W.
Published: December 2007

Along cliff edges of the Niagara Escarpment in Ontario, Canada, Acer saccharum Marsh, is rarely found, but within 5 m of the cliff edge it becomes the dominant species of a rich deciduous forest on the plateau. To discover how age-dependent and microsite-dependent processes combine to control the spatial distribution of this species along the environmental gradient, age structures of natural seedlings and saplings between 1 and 25 years old were investigated over a three-year period. Mortality rates over the monitoring period were highest in 1-year-old seedlings and decreased gradually as age approached 10 years. Both spatial and seasonal variation in environmental conditions affected 1-year-old seedlings most, and these effects declined as seedling age increased. The distribution of types of visible injury preceding death in the 1-year-old seedlings suggested that both drought and herbivory influenced survivorship in this species, but to different degrees at different positions on the gradient. Lower seedling heights closer to the cliff edge in 1- to 10-year-old seedlings suggested that environmental conditions constrained productivity and survival. These results clearly demonstrate that variation in age structures along the gradient was determined by both age- and microsite-dependent processes and that these both contribute to the spatial distribution pattern of A. saccharum. Key words: life tables, survivorship, mortality, cliff, distribution, Acer saccharum, Niagara Escarpment.
Ultrastructural characterization of wood from Tertiary fossil forests in the Canadian Arctic
Authors: Blanchette Robert A. , Cease Kory R. , Abad André R. , Burnes Todd A. , Obst John R.
Published: December 2007

Micromorphological and ultrastructural characterization of fossil gymnosperm wood from Comwallis Island, Axel Heiberg Island, and Ellesmere Island in the Canadian High Arctic showed the changes that have occurred in cell walls of wood during 20–60 million years of burial. No evidence of permineralization was observed. Wood with rounded cells, thick secondary walls, and intercellular spaces was common in all samples. Secondary walls were eroded and swollen. A transition from an organized secondary wall, with altered but visible microfibrillar structure, to an electron-dense, amorphous material was evident in cell walls. The amorphous material appeared to form primarily in the secondary walls near cell lumina and along cracks that extended into the walls. The middle lamellae were often expanded in size and had convoluted shapes. Hemicellulose degradation appeared to precede cellulose degradation. Samples exhibiting cell walls with increased amorphous material had the greatest lignin and lowest cellulose concentrations. Hemicellulose concentration was extremely low in all Eocene and Paleocene samples. The lignin content of Miocene wood was 47.9%, whereas the Eocene and Paleocene samples ranged from 66 to 84%. Tracheids from extensively degraded samples were distorted and collapsed, and in some cases the cells appeared compressed together. Although the residual amorphous middle lamellae and secondary walls were fused together, the outlines of original cells were visible. Chemical analyses and ultrastructural data indicated that a nonbiological degradation was responsible for the deterioration of the arctic fossil wood samples. Key words: wood deterioration, lignin, hemicelluloses, cellulose, wood ultrastructure, coal formation, fossil wood.
The ultrastructure of hyphal anastomoses between vegetatively compatible and incompatible virulent and hypovirulent strains of Cryphonectria parasitica
Authors: Newhouse Joseph R. , MacDonald William L.
Published: December 2007

European hypovirulent (dsRNA-containing) Cryphonectria parasitica strain Ep-50 was paired individually with West Virginia virulent (dsRNA-free) strains Ep 15-7-7 (vegetatively compatible) and EP 7-5-1 (vegetatively incompatible) on cellophane membranes. Four to six hours after anastomoses formed, the strains were preserved using freeze-substitution and observed using transmission electron microscopy. Hyphal anastomoses between Ep-50 and Ep 15-7-7 showed complete cytoplasmic continuity, with microtubules and mitochondria extending through the fusion aperture. Spherical, membrane-bound virus-like particles, measuring 50–90 nm in diameter, were located in the Ep-50 hypha, the Ep 15-7-7 hypha, and the short anastomosis bridge between them. All anastomoses between the compatible strains involved a hyphal peg that grew toward a swelling that developed on the receiving hypha. Fusion took place between the swelling and the lateral wall of the peg. Anastomoses between the incompatible strains showed cellular collapse and cytoplasmic degeneration that extended away from the anastomosis area in hyphae of both strains. Because of this, vegetative incompatibility would seem to be a formidable barrier to hypovirulence conversion and biocontrol of C. parasitica. Key words: Endothia parasitica, hyphal fusion, virus-like particles, hypovirulence conversion.
Decay of date palm wood by white-rot and brown-rot fungi
Authors: Adaskaveg J. E. , Blanchette R. A. , Gilbertson R. L.
Published: December 2007

Wood from trunks of Canary Island date palm (Phoenix canariensis) was decayed for 12 weeks with white-rot fungi (Ganoderma colossum, G. zonatum, Phanerochaete chrysosporium, Scytinostroma galactinum, or Trametes versicolor) or brown-rot fungi (Wolfiporia cocos, Gloeophyllum trabeum, or Fomitopsis pinicola). Using the vermiculite-block assay, white-rot fungi caused significantly more weight loss (63%) than brown-rot fungi (32%). Of the white-rot fungi, G. colossum caused the greatest weight loss (81%), while S. galactinum caused the least (36%). In contrast, weight loss caused by the brown-rot fungi was similar. Chemical analyses indicated that both white-rot and brown-rot fungi caused losses of starch, holocellulose, and lignin. White-rot fungi, however, removed greater amounts of lignin than the brown-rot fungi with three species, S. galactinum, P. chrysosporium, and G. zonatum, causing selective delignification. Scanning and transmission electron microscopy showed that phloem and parenchyma cells were more susceptible to decay than xylem and fiber cells. Starch grains were degraded by all fungi and were nearly removed in wood decayed by G. colossum. In wood decayed by white-rot fungi, cell walls were eroded and middle lamellae were degraded. Selective delignification was observed in fibers adjacent to vascular tissue in wood decayed by the three white-rot fungi. In wood decayed by brown-rot fungi, walls of ground parenchyma and vascular bundle cells were swollen and fragmented when physically disrupted. In wood decayed by F. pinicola, some cell walls were nearly disintegrated. Key words: selective delignification, simultaneous decay, ultrastructure.
A hybrid Isoetes, I. × harveyi, in northeastern North America
Authors: Britton D. M.
Published: December 2007

Fifty-five Isoetes plants from 11 localities were uniformly 2n = 77. These plants were referable to I. harveyi A. A. Eaton, and exhibited hybrid vigour. SEM of spores of the type and other collections had polymorphic spores and exhibited a morphology that ranged from I. macrospora to I. tuckermanii, the putative parents. This common hybrid should be named I. ×harveyi A. A. Eaton pro sp. Key words: Isoetes, hybrid, cytology, SEM.
The relationship between seasonal changes in rhizome carbohydrate reserves and recovery following disturbance in Calamagrostis canadensis
Authors: Hogg Edward H. , Lieffers Victor J.
Published: December 2007

The grass Calamagrostis canadensis (Michx.) Nutt. often forms a dense growth after logging and interferes with replanting on moist sites in northern Alberta. The objective was to determine if seasonal changes in rhizome carbohydrate reserves can provide useful predictions of the time of year when this species is most vulnerable to disturbance. Small (3 × 3 m) plots were mowed to ground level in May, June, July, or August 1988, or on all four of these dates. The lowest seasonal levels of rhizome carbohydrate reserves (10–12%) occurred early in the season (mid-May to early July). Contrary to expectations, in September 1988 the belowground carbohydrate reserves in plots mowed once during this period had increased to levels that were significantly greater (17–18%) than in unmowed control plots (15%). In plots mowed on all four dates, rhizome carbohydrate levels (11%) and biomass were significantly lower than in unmowed plots in September 1988. Despite these differences, regrowth of shoot biomass in 1989 was similar among all mowed and unmowed treatment plots. Thus rhizome carbohydrate levels were a poor predictor of shoot biomass regrowth following disturbance treatments. It is suggested that improvements in microclimate following the removal of shoot biomass and litter may have compensated for the negative effects of disturbance treatments on the plant's carbon balance. Key words: defoliation, biomass, regrowth, TNC, Gramineae.
Stomatal conductance patterns and environment in high elevation phreatophytes of Wyoming
Authors: Foster Jeffrey R. , Smith William K.
Published: December 2007

High-elevation (2305 m) phreatophytes (cottonwood, Populus angustifolia James, and willows, Salix monticola Nutt. and Salix exigua Bebb) in southeastern Wyoming commonly showed a pattern of increasing stomatal conductance (g1) throughout the day, despite minimum leaf water potentials (ψ1) as low as −2.7 MPa. Diurnally, light and leaf temperature were the most important variables influencing g1, but there were also threshold values of ψ1 and leaf-to-air vapor pressure deficit for stomatal closure. Seasonally, maximum daily g1 (gmax) was similar between species, was positively related to minimum air temperature the previous night, and showed a threshold response to soil temperature. Two types of evidence existed for large soil-to-leaf conductances (gs–l) and for liquid water being available to the roots. The first was no change in ψ1 despite increasing transpiration during the afternoon. The second was rapid evening recovery of ψ1 often to values higher than mean soil water potential to 60-cm depth. The combination of low atmospheric pressures at high elevation, large gs–l, and access to a water table may explain how these phreatophytes attained gmax of 0.8–0.9 mol m−2 s−1, much higher than gmax of low-elevation phreatophytes or high-elevation nonphreatophytes. Key words: Populus, Salix, phreatophyte, stomatal conductance, xylem pressure potential.
Distribution and variation of hydroxamic acids and related compounds in maize (Zea mays) root system
Authors: Xie Y. S. , Arnason J. T. , Philogène B. J. R. , Atkinson J. , Morand P.
Published: December 2007

The concentrations of hydroxamic acids and related compounds, 2, 4-dihydroxy-7,8-dimethoxy-1,4-benzoxazin-3(4H)-one (DIM2BOA), 2-hydroxy-7,8-dimethoxy-1,4-benzoxazin-3(4H)-one (HMBOA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3(4H)-one (DIMBOA), and 6-methoxybenzoxazolinone (MBOA), in roots of 1- to 5-week-old maize plants were determined by high-performance liquid chromatography (HPLC). The highest concentrations of DIM2BOA, HMBOA, and total related compounds were found in maize root extracts when maize roots were 2 weeks old and the maize plant was approximately 15 cm in height. The highest concentrations of DIMBOA equivalents were found in 4-week-old maize root extracts. The distribution of individual compounds in different tissues (cortex, stele, and complete organ) of various root parts (first set of nodal roots, secondary roots, primary root, mesocotyl, and adventitious roots from mesocotyl) was also determined. Hydroxamic acids and related compounds are concentrated in the cortex of all parts of maize roots determined except mesocotyl. The concentrations of total related compounds and all individual compounds except HMBOA in complete organ of nodal roots were significantly higher than any other parts of maize roots. The high concentrations of these substances in the cortex of maize root may be relevant in the resistance of maize varieties to subterranean pest insects. Key words: hydroxamic acids, 1,4-benzoxazin-3-ones, maize, root system.
Germination of pollen of the dwarf mistletoe Arceuthobium americanum
Authors: Gilbert Jeannie , Punter David
Published: December 2007

Pollen of Arceuthobium americanum Nuttall ex Engelmann, a parasitic dwarf mistletoe of Pinus banksiana Lamb, in Manitoba, was germinated on media containing a range of concentrations of sucrose and salts. Highest germination levels occurred on 20% sucrose agar; addition of salts significantly depressed germination. Pollen germinability was below 5% at first but increased to near 50% as the season advanced. Mean germination differed significantly between flowers from 10 staminate plants but peaked at approximately the same times in association with increasing temperatures. Freezing night temperatures were followed by reduced germinability. The optimum temperature for in vitro pollen germination is close to 30 °C, whereas 40 °C impairs germination. Key words: parasitic angiosperms, microclimate, jack pine, reproductive biology.
Germination and early seedling growth in some northern wild rice (Zizania palustris) populations differing in seed size
Authors: Counts R. L. , Lee P. F.
Published: December 2007

A field survey of eight northern Zizania palustris populations indicated that there is substantial variation in seed size. Variability is partitioned approximately equally among populations and among individuals within populations. Germination dynamics and temperature sensitivity of germination differed among four populations tested, but the differences were not apparently related to mean population seed size. Mean population seed size did appear to influence the germinability of viable seeds, such that a greater proportion of larger seeds exhibited prolonged dormancy. In a test using three populations differing in mean seed size, those with large seeds produced larger seedlings than populations characterized by small seeds. It appears that in Z. palustris seed size influences whether or not a viable seed will germinate and the size of the resulting seedling, but not the rate at which germinable seeds are recruited to form a seedling population. Key words: Zizania, seed size, germination.
Starch content and activities of starch-metabolizing enzymes in effective and ineffective root nodules of soybean
Authors: Forrest Sharon I. , Verma Desh Pal S. , Dhindsa Rajinder S.
Published: December 2007

Starch content and activities of some enzymes of starch metabolism were determined in wild-type, N2-fixing (fix+) nodules and in two non-N2-fixing (fix−) nodules induced by Bradyrhizobium japonicum mutant strains, T5-95 and T8-1, on soybean (Glycine max L.) roots. The T5-95 nodules are similar to wild type in ultrastructure, but the T8-1 nodules are different in that the bacteroids are not released from the infection thread. After initial accumulation to relatively high concentration, starch was depleted during nitrogen fixation in fix+ nodules. However, in fix− nodules, the accumulated starch was not metabolized. The activity of starch-bound starch synthase (EC 2.4.1.21) declined in fix+ nodules but remained high in fix− nodules. The activity of α-amylase (EC 3.2.1.1) was only slightly higher than wild type in T5-95 but was four times higher than wild type in T8-1 nodules. The activity of starch phosphorylase (EC 2.4.1.1) increased in all nodule types from 14 to 21 days postinfection. A positive correlation was observed between the capacity of nodules to fix N2 and their capacity to degrade starch. Collectively, these results support the concept that starch accumulated during early stages of nodule development is metabolized to supply energy for nitrogen fixation and to meet the metabolic demands of bacteroids. Key words: nitrogen fixation, starch content, effective and ineffective nodules, starch synthase, starch phosphorylase, α-amylase.
The hydraulic architecture of roses (Rosa hybrida)
Authors: Darlington Alan B. , Dixon Michael A.
Published: December 2007

The presence of an abscission zone in the stem of greenhouse roses (Rosa hybrida) between the vegetative and reproductive components was verified. This led to a description of the hydraulic architecture of the rose stem. The structural aspects of the xylem conducting system in stem, abscission zone and peduncle were examined to define their relative roles in the delivery of water via the stem to the transpiring plant surfaces and the extent to which their functional capacity may be influenced by environmental variables such as humidity. The stem exhibited a highly developed xylem with many large-diameter tracheary elements. Contrary to this the distal segment of the peduncle was poorly vascularized. The remainder of the peduncle, which included the abscission zone, was a transition between these two extremes. The abscission zone was a site of reduced hydraulic conductance that was not due to a reduction in the number or size of xylem conduits but to changes in the alignment of the elements. The variable conductances across the abscission zone and peduncle regions may play an important role in floral development and the response of the plant to water stress. Rose plants grown at constantly high humidity (77% RH) did not exhibit significantly different internal anatomical features of the xylem conducting system relative to roses grown in ambient, uncontrolled humidity (30 to 60% RH). Key words: abscission zone, hydraulic conductance, humidity.
Vegetation–environment relationships of an inland boreal salt pan
Authors: Burchill C. A. , Kenkel N. C.
Published: December 2007

Vegetation composition and community structure of boreal inland salt pans near the shore of Dawson Bay, Lake Winnipegosis, Manitoba, were examined. Eight vegetation associations and eight species groups were described from the site. Most of the vegetation associations were dominated by a single graminoid or graminoid-like species. Species composition in the most saline areas was similar to that of prairie salt pans to the south, whereas the vegetation of less saline areas showed affinities to both prairie and boreal forest. Examination of vegetation–environment relationships indicated that soil salinity was the moost important factor determining vegetation pattern. Other soil factors such as nutient levels, bulk density, and percent organic matter were of secondary importance. Species richness increased with decreasing salinity, but trends in Shannon–Weaver diversity and evenness along the salinity gradient were more complex. Despite the salinity gradient being environmentally continuous, strong vegetational discontinuities were noted. It is suggested that these discontinuities arose through interspecific competitive interaction and displacement mediated by differences in the salt tolerance of species. Key words: competition, discontinuity, gradient, halophyte, plant community, salinity.
The structure of the phialides (mucronate hyphopodia) of the Meliolaceae
Authors: Mueller W. C. , Goos R. D. , Quainoo J. , Morgham A. T.
Published: December 2007

Light and electron micrographs of the mucronate hyphopodia of several species of the Meliolaceae showed that these structures consist of a single cell that produces endogenous spores by an extension of the basal cytoplasm. These spores are separated from the basal cytoplasm by a septum and are extruded through an apical pore. Although the function of the spore is unknown, the term phialide seems more appropriate for these structures than the term mucronate hyphopodium. Key words: Meliolaceae, mucronate hyphopodia, phialide.
Intraspecific genetic variation of acid phosphatase activity in monokaryotic and dikaryotic populations of the ectomycorrhizal fungus Hebeloma cylindrosporum
Authors: Meysselle J. P. , Gay G. , Debaud J. C.
Published: December 2007

Intraspecific variability of acid phosphatase activity and mycelial growth of the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi was examined because of the role of this enzyme activity in the phosphate nutrition of the fungus and consequently of mycorrhizal host plants. Interstrain variation was studied with 11 wild strains, and intrastrain variability was studied with 20 sib-monokaryons and 50 reconstituted dikaryons, progeny of the HC1 fruiting strain. The range of variation of acid phosphatase activity among wild dikaryotic mycelia was the same as that among sib-monokaryons or dikaryons belonging to the progeny of a single strain. The total phosphatase activity of the wild strains ranged from 5.70 to 96.0 total milliunits (TmU). It ranged from 11.1 to 120.5 TmU within sib-monokaryons and from 34.2 to 178.1 TmU for reconstituted dikaryons. Specific phosphatase activity of wild dikaryons ranged from 48.5 international milliunits (ImU) to 675.6 ImU, whereas the ranges of variation among sib-monokaryons and reconstituted dikaryons were, respectively, 85.3–791.0 and 270.7–816.1 ImU. On average, sib monokaryons and reconstituted dikaryons had lower activity than their parental dikaryon. However, four reconstituted dikaryons had a higher specific activity than the original dikaryon HC1. The growth of the studied mycelia also varied, but in a narrower range (from 97.1 to 151.6 μg protein per culture for wild dikaryons, from 130.1 to 199.1 μg for sib-monokaryons, and from 160.6 to 275.9 μg for reconstituted dikaryons). No correlation could be detected between specific acid phosphatase activity and growth rate in pure culture within the different monokaryotic or dikaryotic populations studied. These results demonstrate the possibility of obtaining, by intrastrain crossings, mycelia having higher phosphatase activity than the parental wild strains. The characteristics of the different mycelia are discussed in relation to a selection program and their putative spatial distribution in natural conditions. Key words: acid phosphatase, ectomycorrhizal fungus, intraspecific variation, monokaryon, dikaryon, Hebeloma cylindrosporum.
Dynamics of weed populations in a northern subarctic community
Authors: Staniforth Richard J. , Scott Peter A.
Published: December 2007

The introduced flora of Churchill, northern Manitoba, was studied to draw some conclusions about the dynamics of weeds in northern subarctic communities in general. One hundred and six introduced species have been recorded at Churchill. Fifty-five percent of these were "temporary," dying out when original colonizers senesced (e.g., Avena spp., Setaria viridis). Seventeen percent were "established," i.e., able to set viable seed and maintain their populations (e.g., Thlaspi arvense, Crepis tectorum). Twenty-eight percent "persisted" locally by vegetative propagation or repeated seed input (e.g., Linaria vulgaris, Chenopodium album s.l.). The findings were compared with those of an earlier study. The number of species and their local distributions around Churchill have increased in the last 30 years. This may be due to an increase and diversification in the traffic with southern regions or to an amelioration in the climate. Although one in five species in the vicinity of Churchill are introduced, usually fewer than 12 weed species were established at any one site. Abandoned sites exhibited a rapid disappearance of weeds. Depauperate individuals of a few species were found away from inhabited areas, with none occurring in natural communities. Organic material in refuse tips provided a mild environment with a long growing season. Refuse tips may act as refuges for weeds and as potential sources of their seeds. Aliens that were successful at seed production were either perennials, winter annuals, or biennials. These plants flowered early and hence are able to ripen their seeds. Years with long growing seasons may allow seed production in otherwise temporary species. Dynamics of weedy species around Churchill will likely reflect current and (or) future events in other, more isolated northern communities. Key words: subarctic, weeds, introduced plants.
Accumulation of phytoalexins in the compatible interaction between Cladosporium fulvum and tomato in relation to colonization
Authors: Batista Ulisses G. , Higgins Verna J.
Published: December 2007

The production and distribution of the phytoalexin falcarindiol in tomato foliage infected with leaf mold was examined to determine how the fungus Cladosporium fulvum is able to colonize and sporulate in an apparently antifungal environment. In a compatible interaction (cv. Potentate – C. fulvum race 2.3), by 12 and 15 days after inoculation, solvent-extractable falcarindiol and two other phytoalexins from tomato, compound 2 (probably falcarinol) and compound 3 (unidentified), reached concentrations considerably in excess of ED50 values for inhibition of the fungus. In contrast, intercellular (apoplastic) fluids obtained from similarly infected leaflets contained only traces of falcarindiol. ED50 values for germination and germ-tube growth of C. fulvum increased as the incubation time was extended, suggesting that adaptation or recovery was possible at the concentrations tested. In in vitro experiments, C. fulvum appeared to readily metabolize falcarindiol, as did a Lycopersicon cell suspension culture. Binding of falcarindiol to living and dead fungal and plant cells was also observed. Falcarindiol, injected into tomato leaflets, decreased rapidly and was only recovered in trace amounts by 24 h. The results suggest that falcarindiol and probably the two other phytoalexins do not reach sufficient concentrations in the apoplast of an infected susceptible leaf to have an effect on growth and sporulation of C. fulvum. Key words: leaf mold, Fulvia fulva, falcarindiol, falcarinol.
Fern spores in a grassland soil
Authors: Milberg Per
Published: December 2007

Large numbers of fern spores germinated in soil samples from a grassland trail. The trail was established in central Sweden 35 years ago to study the effect of different treatments on grassland vegetation. The density of prothallia varied between 57 000 and 170 000 m−2 in the different treatments. There were no ferns in the treatment plots, and none of the three fern species identified from the spore bank were found in the surrounding area. This suggests that the large spore bank has accumulated over a long period of time and that fern spores are capable of remaining viable in the soil for several years. A large spore bank can enhance the chance for intergametophytic crossing in fern species. Key words: fern, grassland, Pteridophyta, soil seed bank, spore bank.
Neocallimastix: a comparative morphological study
Authors: Wubah D. A. , Fuller M. S. , Akin D. E.
Published: December 2007

The development from zoospore to a mature thallus in Neocallimastix sp. isolated from a Georgia cow was studied at the light microscope level. The zoospore had 9–14 posteriorly directed flagella, and its shape varied from amoeboid in agar to ovoid in broth. Encysted zoospores developed endogenously into extramatrical ovoid or spherical incipient zoosporangia with extensively branched intramatrical rhizoids that often had constrictions. Sessile mature zoosporangia varied in shape, and zoospores were fully formed within zoosporangia before release through an apical pore. In agar, zoospores encysted close to the parent zoosporangium and developed endogenously into second generation zoosporangia or exogenously into elongate thalli. At maturity, an elongate thallus was made up of a sporangium, a sporangial stalk, a cyst, and branched rhizoids. Elongate thalli were sometimes formed in broth. Melanized resting sporangia were formed on branched thalli in old (> 36 h) cultures. Two isolates of Neocallimastix frontalis from a cow and sheep and Neocallimastix patriciarum were grown under the same conditions as our isolate, and the morphology of zoospore, zoosporangium, and melanized sporangium of the four isolates were compared. In broth, the isolates developed in the same manner and formed elongate thalli and melanized sporangia as described for our isolate. There is insufficient justification, based on morphology alone, for separating the four isolates. The importance of basic light microscopy is discussed. Key words: Neocallimastix, development, morphology.
An ultrastructural study on the early development of Zea mays somatic embryos
Authors: Fransz P. F. , Schel J. H. N.
Published: December 2007

Friable embryogenic callus, obtained from immature embryos of Zea mays L., was cultured on N6 medium supplemented with 1 mg/L 2,4-dichlorophenoxyacetic acid, 6 mM proline, and 2% sucrose. Cultured tissue fragments containing several globular embryoids were excised and examined by light and electron microscopy to follow the early development of maize embryoids. The somatic embryos consist of an apical region and a suspensor region. Cells of the apical region are small, cytoplasm rich, and mitotically active. They contain much starch and numerous bundles of microtubules. Suspensor cells are larger and more vacuolated. A high metabolic activity in both cell types is indicated by the presence of many organelles, coated vesicles, and multivesicular bodies. Transition units appear to form intermediate stages between the embryogenic callus cells and the somatic embryo. A transition unit consists of a group of embryogenic cells and shows an apical and a basal region. The unit has many intercellular spaces, and within the cells areas with organelle-free cytosol are frequently observed. Key words: somatic embryogenesis, in vitro culture, ultrastructure, Zea mays L.