bluuebunny/crossref_metadata_2025 huggingface dataset:
Composition and seasonal variation of spore populations of arbuscular mycorrhizal fungi in dune soils on the island of Santa Catarina, Brazil
Authors: Stürmer S. L. , Bellei M. M.
Published: December 2007

A sand dune area in Santa Catarina, Brazil, was surveyed every 3 months to determine species composition and seasonal variation of arbuscular mycorrhizal fungi populations associated with Spartina ciliata. Spores from 12 fungal species were recovered. Overall species richness was 5.9. A plot of rank versus abundance provided an indirect measure of the structure of the fungal community and showed a linear relationship among species. A mean of 298 spores/100 g soil were extracted from sand dune samples, with Acaulospora scrobiculata forming 50.9% of the total population. The most frequently recovered species at all sampling dates were Gigaspora albida, Scutellospora weresubiae, A. scrobiculata, and one undescribed Scutellospora species. Spore abundance ranged from 0 to 69 spores/100 g soil for all species except A. scrobiculata (60–247 spores/100 g). Spore abundance of each species did not vary significantly through the season. However, several general trends were observed. The number of spores of Glomus constrictum, Glomus etunicatum, and Acaulospora sp. (No. 2) was maximal in winter, whereas that of Gigaspora albida peaked in spring. Species composition and richness of arbuscular fungi in Brazilian dunes appear to be similar to those in sand dunes along the Atlantic coast of the United States. Key words: arbuscular mycorrhizal fungi, ecology, sand dunes, spore populations, Brazil.
Two-dimensional mapping of mycelial polypeptides of Ophiostoma ulmi and Ophiostoma novo-ulmi, causal agents of Dutch elm disease
Authors: Jeng Robert S. , Brasier Clive M.
Published: December 2007

Two-dimensional mycelial polypeptide maps were used to compare interspecific and intraspecific relationships among six isolates of Ophiostoma ulmi and four Eurasian and four North American race isolates of Ophiostoma novo-ulmi. The basic polypeptide pattern of O. ulmi differs markedly from that of O. novo-ulmi. A number of polypeptides were identified that could differentiate the two species and one was detected that may discriminate Eurasian from North American races. Overall, a high degree of correlation between species, race, and polypeptides was evident. However, two O. ulmi isolates (MAB and M273) and one O. novo-ulmi isolate (83) exhibited the same unique polypeptides. These isolates otherwise exhibit typical O. ulmi or O. novo-ulmi nuclear DNA polymorphisms. This suggests that they may share a common developmental pathway absent in other isolates examined. In view of this phenomenon, the greatest value of two-dimensional polypeptide gels may lie in the elucidation of proteins involved in species or race specificity, in pathogenesis, or in development rather than in routine species identification. Key words: Ophiostoma ulmi, Ophiostoma novo-ulmi, two-dimensional polypeptide mapping, introgression.
Early seedling development in relation to seed mass and morph in Cakile edentula
Authors: Zhang Jianhua
Published: December 2007

Cakile edentula produces dimorphic seeds from the upper and lower fruit segments. The upper seeds are well adapted to long-distance dispersal and have greater mean seed mass and surface area than those from the lower seeds. Great mean mass of the upper seeds is probably adaptive because it ensured early independent growth of seedlings and thus enhanced their chances of surviving environmental stresses. Large seed reserves also resulted in high chlorophyll content of the cotyledons. Large seed surface area resulted in large cotyledon area and cotyledon area to biomass ratio of the subsequent seedlings, but the adaptive advantage is not clear. Since increased seed surface area necessitates great protective tissues (fruit coat) that may improve the buoyant ability of seeds, large seed surface area of the upper seeds may be a result of selection for dispersal. Key words: seed mass, seed dimorphism, establishment, sand dune, selection, Cakile edentula.
Patterns of leaf phenology in forest understory
Authors: Uemura Shigeru
Published: December 2007

Foliar phenologies of forest understory plants were categorized, and the distribution pattern of leaf habit was examined among different forest environments. Various patterns of foliar phenology were found, especially in herbaceous plants. In addition to the seasonal light regime controlled by the phenology of canopy trees, differences in the length of period with snow cover led to the divergence. Perennial-leaved plants predominate in intensely shaded habitats while annual-leaved plants are more abundant in less shaded habitats. The shade tolerance of perenniel-leaved plants can be considered a preadaptation to snow tolerance. In contrast with the perennial-leaved plants, biennial-leaved plants with leaves overwintering 1 year appear to be favored in euphotic habitats with high insulation both in spring and in autumn. These species are effective competitors in spring because of rapid emergence of current leaves, probably through retranslocation of resources accumulated in the previous year. Another adaptive trait is found in heteroptic plants simultaneously having summer-green leaves and overwintering leaves; these types of leaves seem to function in predictable and quite different environments in a year. Key words: foliar phenology, growth form, light resource, overwintering leaf, snow cover.
Scales of segregation and aggregation of plants of different kinds
Authors: Dale M. R. T. , Powell R. D.
Published: December 2007

This paper introduces a method for examining the scales of segregation or aggregation of two kinds of plants. It uses the mapped positions of plants but is based on methods originally designed for contiguous quadrat data and may be referred to as two-dimensional local quadrat covariance. A complementary randomization procedure makes it possible to test whether observed aggregation is merely the result of overall patchiness. These methods are applied to analyze the spatial pattern of Solidago canadensis L. plants in an old hayfield, with and without insect galls. In many of the 12 plots sampled, the galled and nongalled plants were found to be aggregated at scales around 0.7 m. The randomization test showed, however, that this apparent aggregation was often due to the overall patchiness of the plants' dispersion, and that in some cases, within the patchiness the two kinds of plants were actually segregated at a similar scale. Key words: aggregation, galls, patchiness, pattern, scale, segregation, Solidago canadensis.
Seed yield and biomass allocation in Sorghum bicolor and F1 and backcross generations of S. bicolor × S. halepense hybrids
Authors: Piper Jon K. , Kulakow Peter A.
Published: December 2007

The Land Institute is developing perennial grains to be grown in prairie-like mixtures. One approach involves the development of a perennial grain sorghum by crossing tetraploid Sorghum bicolor with wild S. halepense to combine high seed yield with overwintering ability via rhizome production. We grew tetraploid S. bicolor, F1 hybrid (BC0), and two backcross generations (BC1 and BC2) in a randomized block design to examine total biomass, seed yield, and allocation to plant parts within and across generations. Root, rhizome, stem and leaf, and total biomass decreased from the BC0 to BC2 to S. bicolor generations, whereas panicle mass, seed mass, and reproductive allocation were lowest in the BC0 generation (p < 0.05, ANOVA). Mean seed mass (g ∙ plant−1) was 39.1 in the BC0, 107.3 in the BC1, 84.1 in the BC2, and 92.7 for the S. bicolor parent, which translated into yields of 171.9, 471.6, 396.7, and 407.5 g ∙ m−2, respectively. Reproductive allocation varied from 14.7% in BC0 to 28.9% in BC2 compared with 33.5% in S. bicolor. Mean allocation to rhizomes was 2.71% in BC0 but negligible in BC1 and BC2. There was no relationship between rhizome mass and seed mass within any generation, but there was a positive correlation between total plant mass and rhizome mass in BC0. We divided the BC0 population into four groups with respect to rhizome production and found no significant differences among the groups in plant size or seed yield. Within each generation, reproductive allocation was inversely related to culm mass. The lack of an apparent trade-off between allocation to rhizome versus allocation to seed within any generation supports the possibility of combining within a population high seed yield and production of perennating belowground organs. Key words: backcross, hybrid, perennial grains, reproductive allocation, rhizome, seed mass, Sorghum bicolor, Sorghum halepense.
Production, purification, and antifungal activity of the antibiotic nucleoside, tubercidin, produced by Streptomyces violaceoniger
Authors: Hwang Byung Kook , Ahn Sang Joon , Moon Surk Sik
Published: December 2007

Three antibiotic substances strongly inhibitory to Phytophthora capsici or Magnaporthe grisea were isolated from the broth culture of Streptomyces violaceoniger strain A50. A butanol-soluble mixture of antibiotics from the broth were partially purified by XAD-2 column chromatography. The XAD-2 eluates inhibited the mycelial growth of P. capsici and M. grisea and the development of Phytophthora blight on pepper (Capsicum annuum L.) plants. The antibiotics were separated by silica gel column chromatography and then purified on a Sephadex LH-20 column to yield three peaks of antifungal activity: SF1A, SF1B, and SF2A. The pure antibiotic SF2A was further purified by preparative HPLC and identified as the pyrrolo[2,3-d]-pyrimidine nucleoside tubercidin based on the UV, 1H, and 13C NMR spectral data and other chemical evidence. The antibiotic SF2A and authentic tubercidin showed a high antifungal activity against the plant pathogenic fungi P. capsici, Botryosphaeria dothidea, and Rhizoctonia solani. Key words: Streptomyces violaceoniger, tubercidin, antifungal activity.
Some ecological and demographic characteristics of two growth forms of wild soybean (Glycine soja)
Authors: Ohara Masashi , Shimamoto Yoshiya
Published: December 2007

Ecological and demographic characteristics of two morphologically distinct forms of Glycine soja, namely, the twining and branching forms, were investigated in a riverbank habitat. Besides the morphological difference, the ecological distribution and reproductive characteristics for the two forms were also distinctive. The branching form occurred on the open riverside, while the twining form was found in shady, moist inland areas. The branching form had a much larger individual plant biomass and produced more pods and seeds than the twining form. However, the branching form occurred less frequently because of the high mortality it suffered after flooding and the high percent dormancy of seed in the unpredictably disturbed riverside conditions. Despite its lower seed productivity, the twining form was dominant in stable and predictable inland habitats because of its high percent germination and its subsequent high percent survival. The two growth forms of G. soja clearly represent reproductive and ecological differentiation in relation to environmental stability. Key words: disturbance, Glycine, growth form, hard-coatedness, mortality.
Phytolith analysis of olive oil and wine sediments for possible identification in archaeology
Authors: Tyree E. Loeta
Published: December 2007

Phytoliths are microscopic, amorphous silica or crystalline, inclusions of plant origin that can be of diagnostic value in an archaeological context. This study demonstrated that distinct phytoliths can be extracted from two major extant and ancient crop species: olive (Olea europaea L.) and grape (Vitis vinifera L.). Nonacid digestion of leaves and fruits of two Greek olive cultivars (Megareitiki and Kothreiki) and a Greek grape cultivar (Agiorgitiko) showed that olive and grape contained distinctly different calcium phytoliths and that olive fruit flesh and stone contained sclereids. Olive oil sediment from traditionally produced oil from Greece and Turkey and barrel sediment from traditional Greek red wine were found to contain phytoliths and (or) sclereids corresponding to their fruit of origin. Olive oil could therefore be distinguished from wine, making the nonacid phytolith extraction method a potentially useful alternative to chemical analysis of ancient storage jar residues. Key words: calcium and silica phytoliths, olive, grape, sediment analysis.
Frequency of recovery of myxomycetes from soils of the northern United States
Authors: Kerr Sylvia Joann
Published: December 2007

Soil samples from the northern United States in regions subject to acid deposition and from other regions where acid deposition is not a problem were cultured so that estimates of myxomycete frequency could be made. The presence of myxomycetes, protostelids, cellular slime molds, myxobacteria, and nematodes was recorded as were physical and chemical characteristics of the soils. No significant correlations were noted between the numbers of the soil microorganisms in the enumerated classes. Myxomycetes and protostelids were recovered from only 26 of the 81 soil samples. Their presence was correlated with levels of Ca2+, K+, and organic matter, and they were recovered from acidic soils and from soils in regions subject to acid deposition. Characteristics of soils that yielded cellular slime molds and myxobacteria were also analyzed. Key words: myxomycete, dictyostelid, myxobacteria, pH, acid deposition, soil organisms.
Conditioning effects by neighbors on the growth and form of Trifolium repens
Authors: Turkington Roy , Klein Elena , Maze Jack
Published: December 2007

As an intact clone (one genotype) of Trifolium repens (white clover) grows through a sward, parts of the stolon decay and fragments (ramets) are transplanted into different microenvironments. This common garden study was done to assess the impact this placement has on further development and growth of the new ramets. Genets of T. repens were sampled from each of four origins: from areas in an old pasture dominated by Dactylis glomerata, Holcus lanatus, and Lolium perenne, and from seed. Trifolium from each origin was transplanted into each of three grass beds (Dactylis, Holcus, and Lolium) with three replicates. Cuttings were taken annually for 4 years from all the clovers, transplanted into pots, grown for 10–15 weeks, and a number of morphological characters were measured. There was little indication that individuals of Trifolium grow best in their "home" neighborhoods. Most variation in the data was the result of within-genet variation, i.e., phenotypic plasticity, a response assuring survival in environments that vary over time and space. The effects of grass neighbors on Trifolium is mainly expressed as size differences and the effect of origins and genets mainly as differences in shape. The latter is due, in part at least, to different growth rates of parts relative to each other, the former to all growth rates being modified in a similar fashion. Because origins and genets have a longer history than treatments, these results argue for an evolutionary sequence of first size followed by shape differences. Key words: Trifolium repens, phenotypic plasticity, development, neighborhood effects.
Initial litter properties and decay rate: a microcosm experiment on Mediterranean species
Authors: Gillon Dominique , Joffre Richard , Ibrahima Adamou
Published: December 2007

Twelve leaf litters belonging to 10 Mediterranean species of coniferous and broad-leaved trees and shrubs and grass species were incubated in microcosms in the laboratory at 22 °C and constant humidity for 14 months. Samples were collected at 0.5, 1, 2, 4, 6, 10, and 14 months, the remaining dry weight being measured at each sampling time. At the end of 14 months, the litters had lost between 52 and 74% of their original mass. The comparison of regressions fitted to the various functions showed that for the species studied, the litter mass loss in relation to incubation time best fitted a double-exponential decay function. The mass loss therefore resulted from the simultaneous decomposition of two main compartments, a labile compartment that decreased rapidly (half-life of 20 – 60 days under the experimental conditions) and a resistant compartment that depending on the species, either did not decrease significantly or decreased 10 to 20 times slower than the labile compartment (half-life of 320–630 days). The litters studied could be categorized according to the relative importance of these two compartments. This was related to the initial content of water-soluble substances and of carbon in the litters. It was also strongly correlated with the spectral information of the initial litters obtained by near-infrared reflectance spectroscopy. In contrast, the rate at which the labile and resistant compartments decreased was related to the permeability of the leaves for the former and to their thickness and mass per surface area for the latter. Near-infrared reflectance spectroscopy provides new perspectives for characterizing the capacity of litters to decompose. Key words: litter, decomposition, near infrared reflectance spectroscopy.
Local reduction of mycorrhizal arbuscule frequency in enriched soil microsites
Authors: Duke S. E. , Jackson R. B. , Caldwell M. M.
Published: December 2007

Increased nutrient availability reduces vesicular–arbuscular mycorrhizal (VAM) associations with plants, but whether increased nutrients in small volumes of soil affect local VAM colonization is not known. In a field experiment we investigated VAM colonization at different times following fertilization of small soil patches. Soil volumes of ~ 1000 cm3 were treated with a nutrient solution (enriched patch) or distilled water (control patch) on opposite sides of individual plants of the tussock grass Agropyron desertorum and the shrub Artemisia tridentata. Agropyron had significantly lower (p = 0.03) arbuscular infection in the locally enriched patches compared to control patches (32 and 40%, respectively). This reduced arbuscule frequency was apparent at the first sampling (3 days following treatment application) and remained lower in each subsequent sampling (as much as 30% lower than the control patches). Artemisia revealed a similar pattern in arbuscule frequency but was not statistically significant. Our results suggest that a plant can locally reduce VAM development, since arbuscule frequency specifically was locally reduced even though vesicle and overall infection was not. Since mycorrhizal infection does not increase, we conclude that increased plant root proliferation and uptake capacity are likely to be more important for the exploitation of temporary nutrient pulses or patches than is increased mycorrhizal activity. Key words: arbuscule, nutrient exploitation, phosphorus, reduced development, regulation of colonization, soil heterogeneity, vesicular–arbuscular mycorrhizae.
The Antennaria frieseana (Asteraceae: Inuleae) polyploid complex: morphological variation in sexual and agamospermous taxa
Authors: Chmielewski Jerry G.
Published: December 2007

The Antennaria frieseana (Trautv.) Ekman polyploid complex has been evaluated on numerous occasions without concensus to either the taxa that should be included or their proper ranks. The purpose of this phenetic study was to present a taxonomy for the polyploid complex that is not only independent of a knowledge of chromosome number and reproductive biology but that concurrently reflects morphological variation associated with each. The rank of subspecies (A. frieseana ssp. frieseana and A. frieseana ssp. alaskana (Malte) Hultén) was accepted as the most appropriate level of circumscription that satisfied the purpose of the phenetic study and was supported by the analysis. These subspecies differ with respect to the length of the involucre, inner phyllary length, pappus length, corolla length (the latter subspecies being typically smaller than the former), chromosome number, reproductive biology, and (in part) provenance. Antennaria frieseana ssp frieseana is an agamospermous polyploid, represented by pentaploid (2n = 70) and hexaploid (2n = 84) cytotypes. Antennaria frieseana ssp. alaskana is sexual, probably partially agamospermous (tetraploid cytotype), and either diploid (2n = 28) or tetraploid (2n = 56). Key words: Antennaria frieseana, morphological variation, apomicts, sexual, agamospermy.
Apparent gene flow and genetic structure of Acer saccharum subpopulations in forest fragments
Authors: Ballal Sandhya R. , Foré Stephanie A. , Guttman Sheldon I.
Published: December 2007

Genetic data were collected for glucose-6-phosphate isomerase locus 2 from a sample of the Acer saccharum Marsh. (sugar maple) embryo subpopulations of four forested patches in southwest Ohio and compared with the juvenile (1st-year seedlings to individuals ≤ 1.0 cm in basal area) and canopy (≥ 30 cm in diameter at breast height) subpopulations. Apparent gene flow into each patch was observed as certain alleles found in the embryo subpopulation were not observed in the canopy subpopulation. Genotype frequency data indicated that at least some of the gene flow could be attributed to seed dispersal. Although in some patches, the embryo subpopulation had lower genetic diversity than other subpopulations and was genetically differentiated, it is unlikely that these observed differences represent a change in the genetic diversity of future juvenile subpopulations. Key words: sugar maple, gene flow, genetic diversity, allozyme, forest fragmentation, seed dispersal.
Nitrate assimilation of raspberry and pin cherry in a recent clearcut
Authors: Truax Benoit , Gagnon Daniel , Lambert France , Chevrier Normand
Published: December 2007

An experimental study conducted in a recently clear-cut hardwood forest was used to determine the reduction of nitrate in the leaves of Rubus idaeus L. and Prunus pensylvanica L.F., early successional species and shrub competitors of forest tree regeneration. A factorial experimental design was chosen and the main factors were the shrub competitors and the replicates (blocks). The nitrate reductase enzyme assay was chosen as a physiological marker since it is substrate induced and it is the first key enzyme implicated in the assimilation of nitrate. Results show that for 2 consecutive years, pin cherry had extremely low enzymatic activity in their leaves (0.80 and 0.70 μmol NO2/(g dry wt.∙h)), whereas raspberry always had high values (2.52 and 2.32 μmol NO2/(g dry wt.∙h)). The induction of the enzyme with 800 kg/ha N–P–K fertilizer showed that only raspberry responded to the treatment. These findings could explain the differing peaks of dominance of these early succession species, especially in relation with the changing nitrification rate found in disturbed hardwood forest ecosystems. Pin cherry, a successional shrub reaching maximum abundance following raspberry, clearly does not acquire the large quantities of nitrogen that it does by the uptake of the nitrate form. Nitrogen assimilation of the NH4+ form predominantly would allow pin cherry to short-circuit nitrification by reducing the substrate for nitrification, thus rendering soil conditions less favourable for raspberry and leading to its successional replacement by pin cherry. Key words: disturbed forest ecosystem, nitrate reductase activity, Prunus pensylvanica L.F., Rubus idaeus L.
Salinity and the small-scale distribution of three barrier island shrubs
Authors: Young Donald R. , Erickson David L. , Semones Shawn W.
Published: December 2007

The importance of salinity to small-scale distribution patterns was examined for three shrubs common on barrier islands of the southeastern United States. Field measurements focused on the salt marsh – upland interface zone on Hog Island, Virginia, where Myrica cerifera, Baccharis halimifolia, and Iva frutescens form distinct distributional zones. Although considerable variation in salinity occurred throughout the growth season (June through October), total soil chlorides and groundwater salinity were lowest for M. cerifera, intermediate for B. halimifolia, and highest for I. frutescens. All three species showed similar diurnal and seasonal patterns in stomatal conductance and leaf xylem pressure potential, despite the differences in salinity. However, a laboratory experiment revealed interspecific differences in water relations when the three shrubs were exposed to identical salinity regimes. The field data and water relations experiment indicated M. cerifera is least tolerant to salinity, I. frutescens is most tolerant, and B. halimifolia is intermediate. Seed germination experiments revealed a similar response, except that B. halimifolia was more sensitive to salinity than M. cerifera. The interspecific differences in soil and groundwater salinity, along with the physiological response differences, indicated that salinity may be one of the major environmental factors influencing zonation among the three shrubs; however, the absence of I. frutescens and B. halimifolia in low salinity areas implied that other factors also influence zonation patterns on barrier islands. Key words: Baccharis halimifolia, Iva frutescens, Myrica cerifera, barrier island, salinity tolerance, shrub.
Tirispora, a new ascomycetous genus in the Halosphaeriales
Authors: Jones E. B. G. , Vrijmoed L. L. P. , Read S. J. , Moss S. T.
Published: December 2007

The new genus Tirispora, with the single species Tirispora unicaudata, is described from an intertidal mangrove plant Acanthus ilicifolius in Hong Kong. The genus is compared with other genera with polar unfurling appendages: Aniptodera, Cucullosporella, Halosarpheia, Moana, Ophiodeira, and Trichomaris. Key words: ascus, Halosphaeriales, spore appendages, taxonomy, Tirispora gen.nov., ultrastructure.
Influence of light intensity and water stress on leaf surface characteristics of Cynoglossum officinale, Centaurea spp., and Tragopogon spp.
Authors: Upadhyaya Mahesh K. , Furness Nancy H.
Published: December 2007

Leaf surface characteristics of Cynoglossum officinale, Centaurea diffusa, Centaurea maculosa, Tragopogon dubius, and Tragopogon pratensis, important rangeland weeds of Canada, and effects of light intensity and water stress on these characteristics were studied using scanning electron microscopy. Both adaxial and abaxial leaf surfaces of Cynoglossum officinale were covered with long, uniseriate trichomes with extensive micropapillate sculpturing. The leaf surfaces of Centaurea diffusa and Centaurea maculosa had two types of trichomes: (i) sparsely distributed, multicellular, uniseriate trichomes with ribbon-like chloroform–ether soluble extensions at their tips and (ii) glandular trichomes. Centaurea diffusa and Centaurea maculosa cannot be distinguished on the basis of trichome morphology. No crystalline epicuticular wax was observed on Cynoglossum officinale or Centaurea spp. leaf surfaces. Cynoglossum officinale and Centaurea diffusa uniseriate trichomes became more abundant as light intensity declined. Micropapillate sculpturing on Cynoglossum officinale trichomes disappeared at low light intensities. Ribbon-like extensions at the tips of Centaurea diffusa uniseriate trichomes increased with increase in soil moisture stress. The leaf surfaces of Tragopogon dubius and Tragopogon pratensis lacked trichomes but were covered with tubular epicuticular wax. Tragopogon dubius and Tragopogon pratensis cannot be distinguished on the basis of epicuticular wax morphology. The abundance and size of epicuticular wax crystals on the adaxial leaf surface of Tragopogon pratensis declined with decrease in light intensity and increased with increase in soil moisture stress. Such plasticity of leaf surface morphology may be important in the acclimation of these species to harsh environments. Key words: epicuticular wax, light intensity, moisture stress, scanning electron microscopy, trichomes, weeds.
Assessing the drought-resistance adaptive advantage of some anatomical and physiological features in Nicotiana tabacum
Authors: Rensburg L. van , Kruger G. H. J. , Krüger H.
Published: December 2007

As part of an extensive research programme that attempts to explain and quantify the known difference in drought tolerance of four Nicotiana tabacum L. cultivars, some aspects that may contribute towards the avoidance and tolerance of drought stress were investigated to evaluate overall resistance. The results presented emphasize the adaptive significance of effective leaf movements in determining drought tolerance, by reducing or preventing damage to the photosynthetic system caused by photoinhibition and direct heat damage. Leaf movement seemed to be achieved with greater efficiency by the drought-tolerant cultivars GS46 and Elsoma. Drought stress specifically influenced the carotenoid composition. A strong quantitative correlation existed between the formation of zeaxanthin in the xanthophyll cycle and the type of fluorescence quenching, which is indicative of nonradiative energy dissipation. The latter occurred to a lesser extent in the drought-tolerant cultivars GS46 and Elsoma. This phenomenon also indicated that the rate constant for nonradiative energy dissipation in tobacco remains relatively small in relation to the rate constant for fluorescence during drought stress. Furthermore, irrespective of their drought tolerance, it would seem that tobacco plants have a capability towards starch overproduction, though this was less pronounced in the drought-sensitive cultivars TL33 and CDL28. Owing to anatomical differences, resistance to water flow varied between the respective cultivars, as did the percentage intercellular spaces, both of which correlated positively with the slower decrease in water use efficiency and faster recovery upon rehydration of the drought-tolerant cultivars. Key words: carotenoid composition, chlorophyll a fluorescence, Nicotiana tabacum L., mesophyll surface area, leaf movements.
Dicoma paivae and Dicoma cincerea (Asteraceae), two new species from Somalia
Authors: Ortiz Santiago , Rodriguez-Oubiña Juan
Published: December 2007

Two new species from northeastern Somalia, Dicoma paivae and Dicoma cinerea (Asteraceae), both of section Psilocoma Harv., are described. Dicoma paivae is most similar to Dicoma cana Balf. f. of Socotra Island, from which it can be distinguished by its wider, twisted branches, larger, aristate, conduplicate leaves, smaller capitula, and straw-coloured, coriaceus inner phyllaries. Dicoma cinerea is very closely related to Dicoma schimperi (DC.) O. Hoffm. of northeast tropical Africa and the Arabian Peninsula, from which it can be distinguished by the dense whitish tomentum covering the whole plant and by its broadly ovate to almost orbicular leaves with margins bearing bulbous teeth. Key words: Asteraceae, Dicoma, new species, tropical Africa, Somalia.
Water stress preconditioning of black spruce seedlings from lowland and upland sites
Authors: Abidine Abdenbi Zine El , Bernier Pierre Y. , Stewart James D. , Plamondon André P.
Published: December 2007

One-year-old seedlings from two pairs of upland – lowland populations were subjected to three cycles of drought preconditioning. During a subsequent fourth cycle, preconditioned seedlings and seedlings that had been maintained under well-watered conditions were subjected to a final soil drought. During the drought periods, small but significant differences in gas exchanges and water relations were observed between upland and lowland seedlings but the differences were not consistent either within each lowland – upland pair or over the four cycles. During the final drought period, preconditioned seedlings maintained significantly higher net photosynthesis rate, stomatal conductance, and transpiration rate than unconditioned seedlings. In contrast, no significant differences were found in midday water potential, total sugar content, or water relations parameters between preconditioned and unconditioned seedlings. The results suggest an absence of ecotypic variation with respect to drought tolerance in black spruce. They also suggest that preconditioning in black spruce seedlings occurs mostly through the acclimation of stomatal and photosynthetic mechanisms to drought, without active osmotic adjustment. Key words: Picea mariana, ecotype, gas exchanges, water relations, osmoregulation, preconditioning.
Applicability of abscisic acid and (or) proline accumulation as selection criteria for drought tolerance in Nicotiana tabacum
Authors: Rensburg L. van , Krüger G. H. J.
Published: December 2007

The efficacy of various aspects of abscisic acid and proline accumulation as potential selection parameters for drought tolerance in tobacco was evaluated under controlled conditions. The results indicated that both abscisic acid (though being less pronounced) and proline accumulate rapidly after a distinct threshold leaf water potential value has been reached and that probably because of their higher cell wall elasticity (0.23 and 0.28 MPa for the drought-tolerant cultivars GS46 and Elsoma, respectively, compared with 0.39 and 0.31 MPa for the drought-sensitive cultivars TL33 and CDL28, respectively) these threshold leaf water potential values are reached sooner in drought-tolerant cultivars. However, abscisic acid accumulation precedes proline accumulation in both the drought-tolerant and drought-sensitive cultivars. Proline concentrations increased sharply at a leaf water potential of ca. −1.27 MPa in the drought-tolerant cultivars and at a leaf water potential of ca. −1.50 MPa in the drought-sensitive cultivars. At a leaf water potential of −0.77 MPa the abscisic acid concentrations of all four cultivars were already significantly higher than those of their respective controls and were greater in the drought-tolerant cultivars. The leaf water potential value at which abscisic acid and proline start accumulating rapidly and the accumulated proline end concentrations are recommended as selection parameters for drought tolerance in tobacco. Key words: abscisic acid accumulation, cell-wall elasticity, drought stress, Nicotiana tabacum L., proline accumulation, selection parameters.
The architecture of plant vasculature and transport as seen with magnetic resonance microscopy
Authors: MacFall Janet S. , Johnson G. A.
Published: December 2007

Water and photosynthate transport through plants has been studied extensively for the past three centuries. Few techniques are available that are capable of providing both physiological and anatomical information, and most are destructive in nature. We report the use of high resolution magnetic resonance microscopy (MRM) for the study of intact plant vasculature. Both two- (2-D) and three-dimensional (3-D) image acquisition protocols are employed wherein the plant vasculature can be readily distinguished from surrounding parenchymal tissue. In the 3-D image sets, the vasculature has been digitally segmented, allowing isolation of only the intact vascular architecture. The paths of water and photosynthate transport into several plant specimens have been visualized in this manner. Images of sugar beets, plants that store high concentrations of sucrose within the parenchyma, show contrast patterns between vasculature and parenchyma that are opposite to those seen in images acquired of an apple, fig, okra pod, kiwi fruit, and potato, plants that do not store high concentrations of sucrose. This suggests that transport and accumulation of photosynthates may be partially responsible for contrasts seen within images acquired of these plant specimens. Key words: transport, transpiration, sugar, MRI, magnetic resonance imaging, plants.
Quantitative genetics of stamen fertility in Spergularia salina (Caryophyllaceae)
Authors: Svensson Linus , Persson Helena
Published: December 2007

Heritability of stamen fertility was studied in Spergularia salina (Caryophyllaceae), a selfing annual that shows extensive phenotypic variation in stamen fertility. Variation within and among 70 maternal families, derived from plants representing two natural populations from Sweden, was used to estimate heritabilities of stamen fertility for each of the 10 stamen positions in the flower. The hierarchical design of the study allowed partitioning of variation among four levels of organization using nested analysis of variance. Heritabilities ranged from 0.27 to 0.65 for stamen positions in the antipetalous whorl of stamens and from 0.18 to 0.67 for positions in the antisepalous whorl. When stamen fertility was pooled across all stamen positions of a flower, the heritability was 0.73 in both populations. The nested ANOVA indicated that antipetalous stamen positions have comparatively higher proportions of among-family and among-population variation than the antisepalous stamen positions. Furthermore, highly significant genetic correlations exist between the two antisepalous stamen positions STA 2 and STA 8 and among the other eight positions but not so between these two groups. The relationship between tetraploidization and stamen number reductions in Caryophyllaceae is discussed. Key words: Spergularia salina, stamen fertility, stamen position, heritability, hierarchical analysis of variance, quantitative genetics.
Early dynamic interactions between Fusarium oxysporum f.sp. lini and the roots of Linum usitatissimum as revealed by transgenic GUS-marked hyphae
Authors: Turlier Marie-France , Eparvier Agnès , Alabouvette Claude
Published: December 2007

The aim of this study was to accurately describe the initial processes of flax-root infection by Fusarium oxysporum f.sp. lini. A strain transformed with a GUS gene could be detected by the intense turquoise staining when metabolism was active. The stained fungus was observed on root surfaces in zones where exudation occurred: tips, hairs, rootlets, and wounds. Elsewhere, the mycelium was unstained. The external mycelium penetrated into undifferentiated cells, such as the renewed protodermis cells of the mature root, and the young apical cap cells of the emerging rootlets. The fungus grew and reached the subapical meristem and remained as a permanent internal site of infection. Hyphae grew in and between the undifferentiated cells of the root. When these cells differentiated, the fungus was destroyed in some cells (cortex with endodermis, phloem tubes) but not in others, which became infected cells. The protodermis became the infected cells and hairs of the epidermis. The hyphae did not grow transversely from the epidermis to the stele nor acropetally from apex to the tracheids or vessels. The xylem tissue became infected when it was an undifferentiated group of cells just formed from subapical initials.
Evaluation of the subtribes Moricandiinae, Savignyinae, Vellinae, and Zillinae (Brassicaceae, tribe Brassiceae) using chloroplast DNA restriction site variation
Authors: Warwick S. I. , Black L. D.
Published: December 2007

Chloroplast DNA restriction site data was used to assess relationships among 21 taxa of the subtribes Moricandiinae, Savignyinae, Vellinae, and Zillinae (tribe Brassiceae, Brassicaceae). A total of 301 restriction site mutations was observed, with 154 (51.2%) phylogenetically informative. Cladistic analyses, based on Wagner and Dollo parsimony, indicated two major clades. One of these, the Vellinae–Zillinae clade, included members of the Vellinae and Zillinae, with a clarification of the positions of certain genera. The second, the Brassicinae : Rapa–Oleracea clade included Brassica rapa, Moricandia, Pseuderucaria, and Rytidocarpus. The position of Henophyton (Savignyinae) was not clearly resolved. Within the Vellinae–Zillinae clade, two main lineages were evident: (i) Vellinae-core clade, which includes Boleum, Carrichtera, and Vella (all members of the Vellinae) and Euzomodendron (Savignyinae); (ii) Zillinae clade, which includes Fortuynia, Physorrhynchus, Zilla (all Zillinae), and Foleyola and Schouwia (assigned to Moricandiinae and Vellinae, respectively). The positions of Psychine and Succowia (both assigned to Vellinae) were not clearly resolved in the strict consensus but were aligned with the Vellinae-core clade in almost all of the most-parsimonious Wagner trees. The cpDNA data did not support the current separate subtribal ranking for the Moricandiinae but instead revealed the genetic similarity of Moricandia, Pseuderucaria, and Rytidocarpus to subtribe Brassicinae. Key words: Brassicinae, Moricandiinae, Savignyinae, Vellinae, Zillinae, molecular systematics.
Growth and morphology of rhizome cuttings and seedlings of salal (Gaultheria shallon): effects of four light intensities
Authors: Huffman David W. , Zasada John C. , Tappeiner II John C.
Published: December 2007

Rhizome cuttings and seed of salal (Gaultheria shallon) were cultured in nursery beds at four light intensities (20, 50, and 70%, and full sunlight) created by various thicknesses of shade cloth. After each of two growing seasons, growth and morphological characteristics were compared among light intensities and between life stages. Under all light intensities, rhizome cuttings produced aerial stems and new rhizomes within 1 year and produced fruit within 2 years. Seedlings produced numerous aerial stems but few rhizomes. In general, 70% light induced the greatest production of aerial stems and rhizomes for both cuttings and seedlings. In 70% light, cuttings averaged more than three times the number of rhizomes and rhizome biomass and nearly twice the aerial stem biomass of cuttings in 20% light. Morphology of aerial stems, rhizomes, leaves, and seedling canopies was also affected by light quantity. Aerial stems produced by cuttings were shortest (9.9 cm) in full light and rhizome lengths were longer (27.6 cm) in 50% light than in 20% or full light. Specific leaf area of both cuttings and seedlings was highest (99.9 cm2/g and 146 cm2/g, respectively) under the most shaded treatment. The implications of these results with respect to the ecology of salal under field conditions are discussed. Key words: Gaultheria shallon, seedlings, rhizome cuttings, shade treatment, morphology, vegetative growth.
Growth rate and antibiotic sensitivities of conidium and selfed-oospore progenies of heterothallic Pythium splendens
Authors: Guo L. Y. , Ko W. H.
Published: December 2007

Isolate 167F of Pythium splendens and its four selfed-oospore isolates gave rise to conidium progeny similar to their respective parents in growth rate. However, oospore progeny from these isolates displayed considerable variation in this phenotypic characteristic. These isolates also showed similarity in conidium progeny and dissimilarity in selfed-oospore progeny in sensitivity to streptomycin and chloramphenicol. Among the 117 oospore cultures obtained from isolate 167F, resistance to streptomycin and chloramphenicol was negatively correlated with the growth rates. Results from this study suggest the polygenic inheritance with alternate alleles at each locus for growth rate, sensitivity to streptomycin, and sensitivity to chloramphenicol. Key words: Pythium splendens, conidium progeny, oospore progeny, growth rate, antibiotic sensitivity.
Substrate surface influences upon germination of Colletotrichum truncatum conidia
Authors: Egley G. H.
Published: December 2007

Substrates influenced germination of conidia of the mycoherbicide, Colletotrichum truncatum. Very few (< 10%) conidia germinated when incubated while suspended in water or when incubated on or in partially liquefied agar. Many (> 70%) were induced to germinate when incubated on firm agar. The percentage of germinated conidia increased as agar firmness increased. Not all solid substrates equally influenced germination. Over 50% of the conidia germinated on chromatography paper, cellulose acetate filter, or on hard (plastic cover slip) substrates. In contrast, germination was relatively poor on cellulose nitrate filter and glass cover slips. Some natural substrates of dissimilar texture (wood, live plant leaf) produced good germination. Lower O2 levels or limited gas exchange for submerged conidia did not prevent germination because many conidia germinated while submerged on or between firm substrates. Subjecting conidia to motion during incubation between glass cover slips favored germ tube production rather than appressoria formation. Evidence suggests a positive germination response of C. truncatum conidia to solid substrates that occurs prior to the well-documented thigmotropic response of germ tubes of germinated conidia. Key words: Colletotrichum truncatum, conidia germination, thigmotropism, substrate.
An early Chamaecyparis (Cupressaceae) from the Late Cretaceous of Vancouver Island, British Columbia, Canada
Authors: McIver E. E.
Published: December 2007

Fossil remains of a Chamaecyparis-like member of the Cupressaceae occur in the Upper Cretaceous Comox Formation of Vancouver Island, British Columbia. The cedar bore both flattened, opposite-branching foliage of the Cupressinocladus interruptus type, as well as alternate-branching foliage more similar to that of extant Thuja. Seed cones attached to the foliage are minute, about 3.0 mm in diameter, and consist of four cone scales with abaxial, leaflike umbos. Despite their small size, the structure of the cones and their disposition on axes resembles those of extant species of Chamaecyparis. It is apparent that the Comox cedar is closely related to extant Chamaecyparis and appears to represent an early member of the clade. These data challenge the hypothesis that Chamaecyparis evolved from a Cupressus-like ancestor with large, many-scaled seed cones and terete branches. Key words: Cupressaceae, Chamaecyparis, Late Cretaceous, fossil, seed cones, evolution.
Changes in growth, leaf abscission, and biomass associated with seasonal tropospheric ozone exposures of Populustremuloides clones and seedlings
Authors: Karnosky D.F. , Gagnon Z.E. , Dickson R.E. , Coleman M.D. , Isebrands J.G. , Lee E.H.
Published: December 2007

The effects of single-season tropospheric ozone (O3) exposures on growth, leaf abscission, and biomass of trembling aspen (Populustremuloides Michx.) rooted cuttings and seedlings were studied. Plants were grown in the Upper Peninsula of Michigan in open-top chambers with O3 exposures that ranged from 7 to 92 ppm-h. Depending on the genotype, total seasonal O3 exposure in the range of 50–92 ppm-h had negative impacts on stem, retained leaf, and root biomass accumulation and on diameter growth. Leaf abscission generally increased with increasing O3 exposure and was the principal cause of the decrease in leaf biomass of the O3-treated plants. Considerable genetic variation in O3 responses occurred, as shown by differences in sensitivities among clones and among seedlings. However, the responses to O3 of rooted cuttings and seedlings were similar when seedling means were compared with clonal means for leaf abscission, diameter growth, retained leaf biomass, and root biomass. Comparison of a single square-wave treatment (52 ppm-h) with 70 and 92 ppm-h episodic exposures suggested that the plant response to the square-wave exposure was similar to the response to the highest episodic exposure even though the 92 ppm-h episodic exposure was almost twice the square-wave exposure. Our results are consistent with previous studies that show that P. tremuloides is highly responsive to O3 exposure and this response has a strong genetic component.