bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissecting the Role of the N-Terminal Region of the
Escherichia coli
Global Transcription Factor FNR
Authors: Yan Aixin , Kiley Patricia J.
Published: October 2008

The role of the N-terminal region of the transcription factor FNR, which immediately precedes the first ligand (Cys20) of the [4Fe-4S] cluster, was investigated. We found that truncation mutants that removed residues 2 to 16 and 2 to 17 had wild-type levels of FNR protein but surprisingly altered O
2
regulation.
Abnormalities in pepper (Capsicum annuum) flowers induced by gibberellic acid
Authors: Sawhney V. K.
Published: October 2008

Young pepper plants treated with gibberellic acid (GA3) before the initiation of floral organs produced abnormalities in flowers subsequently formed. The development of petals and stamens was affected by GA3, but sepals and the gynoecium were insensitive to the treatment. The effect on petals was on the unrolling of organs but stamen development was affected more dramatically. GA3 caused abnormalities in pollen development and induced the carpelization of stamens. The expression of feminization of stamens ranged from the production of a few external ovules to a complete transformation of a stamen to a carpel with ovary, style, and stigma. In some instances, the growth of stamens was also inhibited. GA3 also induced supernumerary organs in flowers; all of which were "carpel-like." These and other observations are discussed in relation to the hormonal status and the genetic make-up of plants.
A propos du status taxonomique de Solidago ptarmicoides
Authors: Brouillet Luc , Semple John C.
Published: October 2008

The correct taxonomic position of Solidago ptarmicoides (Nees) Boivin has long been debated. The abundance of hybrids between this taxonand species of Solidago, especially species of Sect. Oligoneuron, suggests an affinity with this group. The white colour of florets in this taxon could be due to a mutation interfering with synthesis of the flavonoids accounting for the yellow color in Solidago. In our study of the genus Aster, we found that phyllary morphology is a very clear character for excluding A. ptarmicoides from the genus Aster and including it into Solidago. This conclusion is suported by other morphological features, such as habit and leaf anatomy, and is strengthened by geographical, ecological, and chromosomal data. It is, therefore, suggested that this taxon be definitely removed from the genus Aster and included in Solidago Sect. Oligoneuron. The following new combination is proposed: Solidago × luteus (= × Solidaster hybridus, × S. luteus). Solidaster and × Asterago are reduced to synonyms under Solidago.
The effect of the hyperparasite (Gliocladium virens) on Rhizoctonia solani and on Rhizoctonia root rot of white beans
Authors: Tu J. C. , Vaartaja O.
Published: October 2008

Using light and electron microscopy, Gliocladium virens is proved to be a hyperparasite of Rhizoctonia solani. When hyphae of G. virens come in contact with those of R. solani, the following sequence of events are observed (i) contact of G. virens with host cells, (ii) formation of appresoria, (iii) penetration of host cells, (iv) formation of intracellular hyphae, and (v) collapse and death of host cells. In vitro, G. virens effectively inhibited sclerotial formation of R. solani.Greenhouse tests showed that the presence of G. virens in soil artificially infested with R. solani reduced at planting the severity of Rhizoctonia root rot in white beans. Root rot severity decreased with increasing concentrations of G. virens. A similar result was obtained in soil treated with the two fungi 2 months prior to planting. This study suggests that G. virens may be a promising biological control agent for Rhizoctonia root rot of white beans.
The developmental morphology of Hypoxylon serpens in culture
Authors: Jensen Jon D.
Published: October 2008

The perithecial development of Hypoxylon serpens (Pers. ex Fr.) Kickx in artificial culture is described. Perithecia develop from initials formed within the vegetative mycelium. Perithecial initials include an ascogonium and surrounding envelope. The ascogonium gives rise to ascogenous elements and eventually asci. The envelope gives rise to all sterile structures, including paraphyses and pseudoparenchyma. Features ofHypoxylon serpens perithecia are representative of the Xylaria-type centrum. The relationship of the Xylaria-type centrum with some other centra is discussed.
Stomatal conductance changes in leaves of McIntosh apple trees before and after fruit removal
Authors: Proctor J. T. A.
Published: October 2008

Daytime stomatal conductance of McIntosh apple leaves was variable and relatively high (1.4 to 3.8 mm s−1) up until fruit removal. Leaf chlorophyll content, total leaf water potential, and specific leaf weight were less variable. Stem water content declined linearly by 10% from mid-August to late October. After fruit removal stomatal conductance, leaf chlorphyll content, and total leaf water potential decreased to low levels. Specific leaf weight did not decline until very late in leaf senescence.A simple model of stomatal response to environmental factors was tested and, following calculation of appropriate parameter values, gave acceptable agreement between measured and calculated stomatal conductances.
Spore discharge in Epicoccum nigrum
Authors: Traquair J. A. , Kokko E. G.
Published: October 2008

Light and scanning electron microscopy of Epicoccum aleuriospores substantiate reports that these spores are forcibly released. Our observations of thin, protruding cross walls between the stalk and adjoining basal cell of the spore, and the circumscissile fracture of the rough outer sheath of the stalk are indicative of an active mechanism of spore release in Epicoccum rather than the passive, lytic mechanism suggested by other workers.
Parasitism of bryophytes by agarics
Authors: Redhead Scott A.
Published: October 2008

Using axenic cultures, Lyophyllum palustre and Galerina paludosa are shown to parasitize Sphagnum in two diferent ways. Other agaric–bryophyte relationships were examined in light of this information. Gemmae are documented for Sphagnum capillaceum.
Pityostrobus mcmurrayensis sp.nov., a permineralized pinaceous cone from the Cretaceous of Alberta
Authors: Stockey Ruth A.
Published: October 2008

A new pinaceous species is described from the Early Cretaceous (Albian) McMurray Formation of Alberta. The cone is partially lignitic with permineralized ovules, 13 cm long × 4 cm wide, and occurs in a siliceous sandstone matrix. Thin sections were made after embedding with bioplastic and infiltration of cut faces with epoxy. Externally the helically arranged flattened cone scales resemble those of extant Picea. Scales bear two inverted, winged ovules containing shrunken nucellar and megagametophyte tissue. The cone axis is slender and contains small wedges of secondary xylem lacking resin canals. Vascularization of the cone–scale complex is similar to the non-Pinus species of the Pinaceae with bract and scale traces separate at their origins. One large abaxial resin canal, 1 mm in diameter, accompanies the traces out into the scale for 1 cm before branching. Two large bundles of sclerenchyma accompany the scale vascular tissue and may have served to open the cone at maturity. The bract, small and triangular in outline, has a terete trace and two lateral resin canals. Cone and seed structure are closely comparable to fossil pinaceous genera Pseudoaraucaria and Pityostrobus and the non-Pinus genera of the extant Pinaceae.
Copper, nickel, and thallium uptake by the lichen Cladina rangiferina
Authors: Burton M. A. S. , LeSueur P. , Puckett K. J.
Published: October 2008

Metal uptake studies with Cladina rangiferina showed that the affinity for nickel was much lower than for copper or thallium. Nickel uptake was not decreased by the absence of light or oxygen or by pretreatment with metabolic inhibitors. Nickel uptake was not temperature dependent but was very dependent upon pH.Cation-exchange studies demonstrated that there was a stoichiometric exchange of Ni2+ for Sr2+, and Cu2+ for Sr2+. The exchange of Tl+ for Sr2+ was not stoichiometric, excess Tl+ was accumulated in relation to the Sr2+ released. The ratio of Sr2+:Tl+ exchange increased with increasing Tl+ availability from 1:9 (12.5 μmol Tl+ available/g of lichen) to 1:2 (500 μmol Tl+ available). Acid-treated lichen gave the expected exchange ratio of 1:2. Washing of the thalli with deionized water resulted in the continued loss of Tl+ from acid-treated and live C. rangiferina. Copper and nickel were not released in this manner.Increasing concentrations of copper and thallium produced a corresponding loss of potassium from the thallus. The potassium loss was initiated at low concentrations of copper and thallium whereas very high concentrations of manganese and nickel were required to bring about the same response.
A comparison of the death induced by fungal invasion or toxic chemicals in cowpea epidermal cells. II. Responses induced by Erysiphe cichoracearum
Authors: Meyer Susan L. F. , Heath Michèle C.
Published: October 2008

Cowpea leaves were inoculated with the plantain powdery mildew fungus, Erysiphe cichoracearum, and fresh epidermal cells overlying veins were examined by light microscopy before being cleared or prepared for electron microscopy. Fungal appressoria usually formed a haustorium in the underlying nonhost cell, but only after what appeared to be an unsuccessful penetration attempt that induced a transient cytoplasmic aggregate, a ring of autofluorescence in the plant wall (best seen in cleared tissue), and in two examples observed ultrastructurally, a small penetration peg embedded in a callose-like papilla. The haustorium developed from a different penetration peg and elicited the death of the invaded cell. As reported for the death of cowpea epidermal cells elicited by CuCl2, cytoplasmic changes that occurred rapidly in fresh tissue after cytoplasmic streaming had stopped correlated closely with changes in ultrastructure. Compared with the CuCl2 study, microtubules and Golgi bodies disappeared faster and membranes appeared more disorganized. These data suggest that in cowpea epidermal cells, ultrastructural changes accurately predict the onset of cell death and may also reflect differences in its modes of induction.
Genetic basis of dormancy and differential response to sodium azide in Avena fatua seeds
Authors: Jana S. , Upadhyaya M. K. , Acharya S. N.
Published: October 2008

Seven crosses, involving either nondormant × dormant or dormant × dormant pure lines of wild oats (Avena fatua L.), were made. Selfing of the hybrid and further hybridization were carried out to produce the F2 and reciprocal backcross generations. The seed germination time-course curves of the parents, their F1, and segregating generations over a 20-week period were studied. Differences in time course of germination in these generations were interpreted in terms of a minimum of three interacting loci. Two pure lines, AN51 and MO73, differed in their response to sodium azide, a respiratory inhibitor, with the former being more responsive. In crosses between these lines, the F1 seeds were also more responsive when AN51 was used as the maternal parent. This differential response of two dormant pure lines and their reciprocal F1s suggests maternal influence in germination response to sodium azide.
The use of complementary fractures and low-temperature scanning electron microscopy to study hyphal – host cell surface adhesion between Uromyces viciae-fabae and Vicia faba
Authors: Beckett A. , Porter R.
Published: October 2008

A modified specimen stub, for use with the EMscope SP2000 Sputter Cryo Preparation Unit, that will facilitate the production of complementary fracture faces is described. The application of complementary fractures for studying hypha–host surface adhesion within freeze-fractured leaves is reported for the first time. Freeze fracturing results in the rupture of either the hyphal wall or the host cell wall or both, at the edge of, or just beyond, the adhesive matrix pad that binds the two together. The implication that the adhesive is stronger than either of the two individual apposed walls is discussed in relation to the mechanics of bonding and to the process of penetration of the host cell by the fungus.
Spotted knapweed germination response to stratification, temperature, and water stress
Authors: Eddleman L. E. , Romo J. T.
Published: October 2008

Spotted knapweed (Centaurea maculosa Lam.) is an introduced noxious weed on grasslands in the northwestern United States and adjoining Canadian provinces. This research examined germination responses of spotted knapweed to stratification, temperature, and water stress under controlled conditions. Immediately after harvest, germination was sharply reduced by sub- and supra-optimal temperatures and water stress; as seeds aged, germination increased at sub- and supra-optimal temperatures. Total germination was enhanced and days to 50% of final germination (D50) was reduced by cool–moist stratification. Under water stress, germination of unstratified seeds was limited at suboptimal temperatures, but seeds pretreated with cool–moist stratification germinated more rapidly and to a higher percentage over a broader range of temperatures and osmotic potentials.
Chromosome numbers of some North American species of Artemisia (Asteraceae)
Authors: Stahevitch A. E. , Wojtas W. A.
Published: October 2008

Chromosome number determinations are reported for 58 accessions, comprising 13 native and introduced taxa of Artemisia found in Canada and the United States. Chromosome numbers observed were n = 8, 9, 18, and 27. A chromosome number of 2n = 18 is the first report for A. pacifica Nutt. A new tetraploid cytotype (2n = 36) was found in A. frigida Willd. Supernumerary chromosomes (n = 9 + 3) and mixoploidy (n = 18, 36) were also observed in this taxon for the first time. Heteroploidy was present in several species. In some taxa, morphological or ecological differences between the chromosomal races were detected; in other cases no differences were noted. Karylogical and phylogenetic evidence is presented for the original chromosome number in Artemisia having been x = 9.
A rapid technique using epoxy resin Quetol 651 to prepare woody plant tissues for ultrastructural study
Authors: Abad A. R. , Cease K. R. , Blanchette R. A.
Published: October 2008

A new technique was evaluated for rapid preparation of woody plant tissues for transmission electron microscopy. A low-viscosity medium formulation was developed using a water-soluble epoxy resin, Quetol 651. No dehydrating solvents were needed during preparation. Samples from living trees and xylary tissues of sound and decayed wood were studied to assess the quality of the media and embedding techniques. Infiltration, preservation of ultrastructural detail, sectioning qualities, and staining of the wood samples were found to be very good. The technique provided a fast, reliable method for preparing wood samples for ultrastructural observation.
Immunohistochemical studies of compatible and incompatible interactions of potato leaves with Phytophthora infestans and of the nonhost response to Phytophthora megasperma
Authors: Cuypers Beate , Hahlbrock Klaus
Published: October 2008

Compatible and incompatible interactions with appropriate pathotypes of Phytophthora infestans (Mont.) de Bary (Pi, races Pi1and Pi4, respectively) and the nonhost response to Phytophthora megasperma f.sp. glycinea Kuan & Erwin (Pmg) were studied microscopically in leaves of one potato cultivar (Solanum tuberosum L. cv. Datura, carrying the Pi-resistance gene R1). Fungal growth was followed by immunohistochemical detection of hyphae in the plant tissue. The reaction of plant cells to the different pathotypes was monitored by staining with aniline blue (callose formation), autofluorescence (accumulation of phenolic compounds), and critical observation of the cell morphology, particularly the appearance of necrosis. Rapid responses occurred in epidermal cells in all types of interaction. Mesophyll cells responded rapidly only in incompatible interactions. Thus, all plant cells surrounding Pmg or Pi4 hyphae showed the hypersensitive reaction, which was rarely observed in the mesophyll of Pi1-infected leaves. This difference was more characteristic of the response of this system than either the timing of hyphal growth or the reaction of epidermal cells at the site of inoculation.
Effect of fire on the mycorrhizal ecology of little bluestem (Schizachyrium scoparium)
Authors: Dhillion Shivcharn S. , Anderson Roger C. , Liberta Anthony E.
Published: October 2008

Fire in a prairie significantly affected subsequent vesicular–arbuscular mycorrhizal (VAM) fungal colonization and sporulation, plant aboveground production, and tissue inorganic nutrient concentration. Colonization levels of VAM fungi in little bluestem (Schizachyrium scoparium (Michx.) Nash) roots were significantly (p < 0.05) lower on the burned site than on the unburned site during the first growing season postburn, but there were no significant differences between sites during the 2nd year. On each sampling date during the first growing season postburn, the burned site had significantly higher aboveground production than the unburned site. Significantly higher tissue levels of available K, Ca, and Mg were found on the unburned site than on the burned site; however, when nutrients were expressed in terms of nutrients in tissue per square metre, there were no significant differences between the burned and unburned sites. Spore counts for soil collected from the rhizosphere of little bluestem and randomly on burned and unburned sand prairies decreased from May into summer and then increased in late summer and fall on both sites during the first growing season postburn. Rhizosphere spore numbers were significantly lower on the burned site than on the unburned site in May and June, but they were significantly higher on the burned site in October during the first growing season. The results suggest that the response of VAM fungi to fire may be attributable to changes in the host plant and not due to any direct effect of fire.
Absorption of nutrient exudates from terrapin eggs by roots of Ammophila breviligulata (Gramineae)
Authors: Stegmann Edwin W. , Primack Richard B. , Ellmore George S.
Published: October 2008

Ammophila breviligulata Fem. is a dominant grass in the nutrient-poor soil of sand dunes along the east coast of North America. More than half its range overlaps that of Malaclemys terrapin Schoepff., a brackish water turtle nesting in sand dunes. Roots of A. breviligulata often proliferate around buried terrapin nests. Gamma spectrometry was used to determine whether nutrients are translocated from terrapin eggs into A. breviligulata. Eggs, collected in the field within 48 h of being laid, were injected with 75Se, 137Cs, 54Mn, and 59Fe. Labelled eggs were covered with dune soil in pots containing A. breviligulata. Plants were then monitored over 15 weeks for the appearance of isotopes. Within 45 days, all isotopes except 59Fe were found in aerial shoots, more than 30 cm from buried eggs. Iron was absorbed but remained in the roots. The other three isotopes steadily accumulated in shoots for 90 days, after which they began to be translocated to underground tissues. Thus, A. breviligulata absorbs nutrients exuding from buried terrapin eggs, utilizing this novel nutrient supply in mineral-deficient soils of barrier dunes.
Low levels of ozone increase bean leaf maintenance respiration
Authors: Amthor Jeffrey S. , Cumming Jonathan R.
Published: October 2008

Pinto bean (Phaseolus vulgaris) plants were exposed to charcoal-filtered air with or without added low levels of ozone (90 nL∙L−1). Dark respiration (CO2 efflux) by expanding primary leaves of the plants was measured and mathematically partitioned into growth and maintenance components. The growth respiration coefficient was unaffected by ozone, whereas the maintenance respiration coefficient increased 15%. Such a relative increase in maintenance respiration results in a diversion of energy and metabolic intermediates from growth processes.
Temporal sequence of cytological events in rice leaves infected with Pyricularia oryzae
Authors: Peng You-Liang , Shishiyama Jiko
Published: October 2008

A time-course investigation was made of early events in leaves of four rice cultivars following inoculation with Pyricularia oryzae Cavara race 131. The pathogen conidia germinated and formed appressoria at a similar frequency in all four cultivars. A difference was found in fungal penetration frequency among the cultivars but it did not appear to be related to race-specific resistance. Growth inhibition of infection hyphae was pronounced in incompatible race–cultivar combinations relative to compatible ones, and a correlation between inhibition of infection hyphae and expression of race-specific resistance was found. The cultivars showed five types of cellular reactions to the pathogen. Light browning and aniline blue staining of the epidermal cell wall (type B reactions) were the first reactions observed in all cultivars and a decrease in their frequency was followed by an increase of other cellular reactions such as cytoplasmic granulation or cell necrosis. This result suggested that cytoplasmic granulation or cell necrosis might be generated from type B reactions. Compared with compatible cultivars, incompatible ones showed type B reactions much more rapidly. The study also revealed the temporal coincidence between inhibition of growth of infection hyphae and occurrence of type B reactions.
The temporal relationship between the development of intracellular hyphae and haustoria by Physopella zeae in Zea mays
Authors: Heath Michèle C. , Bonde M. R.
Published: October 2008

To investigate the developmental relationship between haustoria and intracellular hyphae, fixed and cleared whole mounts of com leaves infected with the tropical corn rust fungus Physopella zeae (Mains) Cumm. & Ramachar were examined by interference contrast light microscopy. Haustoria were clearly distinguished from intracellular hyphae by their morphological differentiation into a filamentous body and a narrow neck. The latter was encircled by a thin neckband, which appeared to develop in young haustoria at the time when the haustorial body started to expand. Observations made at the colony margins suggested that the fungus grew into uninvaded epidermal tissue in the following sequence: (i) formation of a haustorium from a haustorial mother cell in an adjacent cell, (ii) formation of an intracellular hypha next to the haustorium by the same intracellular hypha that had formed the haustorial mother cell, (iii) growth of the intracellular hypha within the newly invaded plant cell, (iv) formation by the intracellular hyphae of haustorial mother cells against the plant cell wall adjacent to an uninvaded cell, and (v) formation of haustoria in the uninvaded cell. These results support the previous suggestion that the haustorium may induce a state of susceptibility in the plant cell, "paving the way" for invasion by the intracellular hyphae.
Eocronartium muscicola: a basidiomycetous moss parasite exploiting gametophytic transfer cells
Authors: Boehm E. W. A. , McLaughlin D. J.
Published: October 2008

The host–parasite interface in Eocronartium muscicola, Auriculariales sensu lato, was examined histologically for 6 of the 21 reported moss hosts, using light microscopy, scanning electron microscopy, and transmission electron microscopy. A unique mode of fungal biotrophy was encountered in 5 of the 6 mosses analyzed, in which E. muscicola exploits gametophytic host transfer cells concomitant with varying degrees of supplantation of the moss sporophyte. Basidiocarps are restricted in these mosses to postfertilized archegonia, in which they are seen to associate with the sporophyte foot region, where they gain access to the host transfer cell nutritional interface. Basidiocarp ontogeny is presented as it relates to the development of the host–parasite interface. The relationship of E. muscicola to other simple-septate auricularioid taxa and the the Uredinales is discussed.
The influence of plant density on flower, fruit, and leaf demography in bush bean, Phaseolus vulgaris
Authors: Doust Jon Lovett
Published: October 2008

The influence of plant population density on bush beans is analyzed in terms of its effect on flower, fruit, and leaf demography, biomass, and yield. Plants grown at the lowest density (solitary plants) did best in terms of leaf production, total leaf days, flowers, and production of marketable pods (i.e., having at least one seed). These plants also accumulated more biomass and had greater numbers of all components of yield. In addition, they showed greater proportionate allocation to reproduction. In all density treatments the second flower cohort (produced 33–35 days after seeds were sown) made the greatest contribution to yield (43–78%). When flower production began, the rate of leaf initiation declined; leaf mortality seemed coupled to the onset of fruit production and was most severe in plants that had many pods to mature. The probability that flowers produced under any density regime would become pods and that these pods in turn would become marketable pods was assessed. Pod production was broken down into two stages: the transition from flower to fruit and from fruit to marketable pod. The results suggest that the transition from flower to fruit is not resource-limited, but the transition from fruit to marketable pod is dependent on current resource supply. When the data are examined on a per pot basis, plants at the highest density were most productive in terms of nonproductive tissues. However, an intermediate density (equivalent to 200 plants/m2) produced the greatest total reproductive biomass and the greatest number of marketable pods per unit area. The value of leaf and flower demography as measures of uniformity of maturation, optimal planting density, and cultivar performance is discussed. Key words: density, flower demography, fruit demography, leaf demography, Phaseolus vulgaris, yield.
Pollen morphology and taxonomy in North American Labiatae
Authors: Trudel Marie Claude G. , Morton J. K.
Published: October 2008

Pollen morphology is described and illustrated based on SEM studies of 118 species of Labiatae (Lamiaceae) native to North America. These include representatives of all the 36 native genera. Pollen in this family is subspheroidal and either tricolpate (subfamily Lamioideae) or hexacolpate (subfamily Nepetoideae). In most of the genera and species, the tectum is conspicuously perforated with or without a supratectal reticulum. A key to facilitate identification of the pollen of the North American Labiatae is provided. The value of pollen as a taxonomic character in this family is discussed. Pollen provides the primary basis for recognition of subfamilies in the Labiatae, but at the tribal level only the Ajugeae has distinctive pollen. Several genera, notably Collinsonia, Salvia, Teucrium, and Trichostema, have pollen that is very different from other genera in this study. At the infrageneric level pollen provides valuable taxonomic characters in several genera, notably Hyptis, Monardella, Salvia, Stachys, Teucrium, and Trichostema. Key words: Labiatae, Lamiaceae, pollen, SEM, North America.
Factors affecting red-osier dogwood seed germination
Authors: Acharya S. N. , Chu C. B. , Hermesh R. , Schaalje G. B.
Published: October 2008

Seeds from 55 populations of native Alberta red-osier dogwood (Cornus stolonifera Michx.) were collected over 2 years (1984 and 1985) to determine the range of variability for seed germination and the effect of ecoregion and moisture conditions in the collection sites on this trait. Each year the unscarified seeds were stored at 3 °C for 30 days, stratified at 3 °C for an additional 30 days and then incubated on an 8 h light: 16 h dark cycle at a temperature of 25:10 °C (light:dark) for germination. A wide range of germination percentages was observed among populations collected in any 1 year. However, the variability was not due to the ecoregion or moisture condition of the collection site. Germination percentage of populations collected in 1984 and 1985 formed five and seven groups, respectively. A study involving eight sites that were common to 1984, 1985, and 1986 revealed a significant effect of population on seed germination. This population effect was not obscured by the combined effects of year, precipitation, temperature, and seed size. The year effect was significant only when population was used as a covariate. Precipitation during seed formation significantly influenced germination performance even after adjustments were made for population and year. Seed germination in red-osier dogwood appears to be influenced by the population from which the seeds are collected and by yearly environmental fluctuations. Therefore, germination studies in this species must include seeds from diverse populations collected over several years. Key words: red-osier dogwood, Cornus stolonifera Michx., germination, population, environment.
A scanning electron microscope study of the pollen tube pathway in pistils of Rhododendron
Authors: Palser Barbara F. , Rouse John L. , Williams Elizabeth G.
Published: October 2008

The pollen tube pathway was observed at regular intervals in pistils of four species of Rhododendron, with emphasis on Rhododendron fortunei. Rhododendron is characterized by a nonpapillate wet stigma, angled stylar canal, placentae with central clefts, and many unitegmic anatropous ovules. Receptive stigmas were hand-pollinated with self pollen 1 – 8 days after anthesis. The pollen, which occurs in permanent tetrads, started germinating during the 1st day. After crossing the stigma surface to one of the grooves leading into the stylar canal, pollen tubes grew straight through the style, and continued into the placental clefts from which they emerged onto the placental surface to grow among the ovules. Tubes reached the ovary in 5 – 10 days depending on the species and took several days after entering the upper ovary to reach the base of the placentae. Single tubes (rarely two or more) diverged from the interovular network and grew under the integument (which is close against the placental surface) to enter the slit-like micropylar opening of an ovule. The morphology of the micropylar slit and the direction of pollen tube entry showed variation among ovules. In R. fortunei ovule entries occurred first on the upper half of the placenta, though not at the top, and in ovules closest to the placental cleft. All portions of the pathway, from stigma surface to micropylar opening, are covered by exudate. Stigmatic exudate increased in amount and became more viscous after pollination, burying the pollen grains and tubes, then gradually dried. Exudate was produced in the style and ovary whether or not pollination occurred. Characteristics of the pollen tube pathway in Rhododendron are discussed relative to those in other angiosperm taxa. Key words: Rhododendron, pollen–pistil interactions, fertilization, transmitting tissues, pistil exudates, ovule entries.
Fungi and cellulolytic activity associated with decomposition of Bauhinia purpurea leaf litter in a polluted and unpolluted Hong Kong waterway
Authors: Au D. W. T. , Hodgkiss I. J. , Vrijmoed L. L. P.
Published: October 2008

A survey of fungal succession on decomposing Bauhinia purpurea L. leaves in the unpolluted Tai Po Kau Forest Stream (TPKFS) and the animal waste polluted Lam Tsuen River (LTR) was carried out during the winter of 1988 and the summer of 1989. In situ cellulolytic activity of the TPKFS leaf litter was also investigated. Most of the 28 aquatic hyphomycete species found were cosmopolitan or frequently reported in temperate regions. Clavariopsis aquatica De Wildeman, Lunulospora cymbiformis Miura, and Flagellospora penicillioides Ingold were the dominant species at both sites. Among the 49 geofungi species recorded, lymaphilic species were commonly observed in the polluted LTR (e.g., Geotrichum candidum Link ex Leman, Fusarium oxysporum Schlecht, and Mucor racemosus Fres.) and lymaxenes in the TPKFS (e.g., Humicola spp., Trichoderma spp. and Gliocladium roseum Bain.). Species richness of aquatic hyphomycetes was higher in the TPKFS (27 species) than in the polluted LTR (14 species), whereas for the associated geofungi, it was higher in the LTR (35 species) than in the TPKFS (28 species). Conidial production was also higher in the TPKFS. Aquatic hyphomycetes and geofungi showed a complementary sequence of dominance in winter and summer, respectively, in the clean TPKFS. Higher cellulolytic activity occurred in the winter than the summer leaf litter. Key words: aquatic hyphomycetes, geofungi, leaf litter, pollution, cellulolytic activity.
Les bruyères in vitro. IX. Édification du système racinaire adventif chez l’Erica ×darleyensis; mise en évidence d'une rythmicité
Authors: Viémont Jean-Daniel , Beaujard François
Published: October 2008

Cuttings of Erica ×darleyensis were cultured in vitro on a medium containing nitrogen in the nitrate form. Development of foliar shoots from axillary buds and the growth of the root system were studied. Appearance and growth of roots were irregular. Periods of rest alternated with periods of rapid growth. Foliar shoots also emerged in a rhythmic manner. The bursts of root growth began a little before or during the rest period of the foliar shoots and went on during leaf expansion. The maximum growth of roots and shoots took place soon after burst following a rest period. Key words: root system, rhythmic growth, Erica, in vitro.
Influence of canopy microclimate on incidence and severity of dogwood anthracnose
Authors: Chellemi Dan O. , Britton Kerry O.
Published: October 2008

Incidence and severity of dogwood anthracnose within the interior and exterior canopies of exposed dogwood (Cornus florida L.) trees and canopies of understory trees were recorded over a 53-day period during the summer of 1990. Concurrent measurements of vapor pressure deficit, air temperature, evaporative potential, and photosynthetically active radiation within the canopies were also recorded. Disease incidence was significantly lower in the exterior canopy of exposed trees than in other canopy locations. Disease severity was significantly different among all three canopy locations, with the lowest severity in exterior canopies of exposed trees and the greatest severity in canopies of understory trees. Of the climatic variables measured, evaporative potential provided the most consistent contrast among microclimates at the various canopy locations. Mean evaporative potentials averaged over 6- to 10-day intervals ranged from 0.00 g H2O h−1 in understory and exposed, interior canopies to 0.40 g H2O h−1 in exposed, exterior canopies. Disease incidence and severity were greater in canopies associated with low levels of evaporative potential. Key words: Cornus florida L., dogwood anthracnose, canopy microclimate, evaporative potential.
Natural hybridization between Stellaria longipes and Stellaria borealis (Caryophyllaceae)
Authors: Emery R. J. N. , Chinnappa C. C.
Published: October 2008

Multivariate principal components analyses of seven morphological characters of a putative hybrid population (located at Plateau Mountain, Kananaskis, Alberta) indicated the occurrence of hybridization between Stellaria longipes and Stellaria borealis. Although the putative hybrid population had intermediate morphology between the two species, it clustered closer to that of S. longipes. Electrophoretic analysis of 15 isozyme loci confirmed that the putative hybrid population was a result of hybridization and possibly introgression. Unique alleles of both species were present in the hybrid, although they were more often attributable to S. longipes. The genetic identity and the level of genetic variability of the hybrid was of an intermediate level between the two species, but closer to that of S. longipes. Key words: natural hybridization, Stellaria longipes, Stellaria borealis, introgression, isozymes.
Host – parasite relationships between the fungus Leptosphaerulina crassiasca and peanut
Authors: Wu Mei-Lee , Hanlin Richard T.
Published: October 2008

The mode of penetration and infection of the peanut leaf by Leptosphaerulina crassiasca were studied by means of light and electron microscopy. The attachment of the multicellular ascospores to the leaf surface was by a mucilagenous sheath that covered the ascospores at maturity. This sheath expanded rapidly in moisture and it extended along the germ tube as it elongated. Two types of germ tubes appeared to be formed, a short one and a relatively long one. Short germ tubes were not delimited by septa, and they penetrated the cuticle and host epidermal cell wall directly without appressorium formation. Penetration occurred 2–6 h after inoculation. The wall was breached by a relatively broad infection hypha that expanded in width inside the host cell wall. The lack of mechanical rupture at the infection site indicated that penetration may involve enzymatic activity. Intracellular hyphae were present in the epidermal cells, but only intercellular hyphae occurred in the palisade and spongy mesophyll tissues. The intercellular hyphae were frequently appressed to the outer surface of the host cell wall. Infected areas rarely exceeded 1 mm in diameter, and they were only sparsely colonized by hyphae of the pathogen. Host cells in the vicinity of hyphae underwent senescence and death. One to 2 months after inoculation, pseudothecia formed in the dead tissues of detached leaves. In some instances the presence of penetration hyphae by short germ tubes induced the formation of a papilla inside the host cell wall, which either restricted growth of the infection hypha or resulted in the death of the germ tube and the cell from which it arose. Long germ tubes were delimited by simple septa and they terminated in an appressorium; however, details of their behavior were not studied. Key words: Arachis hypogaea, Ascomycotina, Dothideales, leaf scorch, pepper spot.
Isolation and characterization of a mycovirus from Plasmopara halstedii
Authors: Mayhew D. E. , Cook A. L. , Gulya T. J.
Published: October 2008

A virus was isolated from Plasmopara halstedii, the causal agent of sunflower downy mildew. The virus contained two species of ssRNA with molecular weight (MW) of 1.05 × 106 and 0.53 × 106. One polypeptide with a MW of 37.5 × 103 was associated with whole virus. Purified preparations consisted of two components, the top component consisting primarily of empty shells. The A260/A280 UV absorbance ratio for the bottom component ranged from 1.25 to 1.35. The partially purified virions were isometric, approximately 32 nm in diameter, and had projections of approximately 4 nm on the virion surface. This virus may be related to the type A virus in Sclerophthora macrospora. Key words: mycovirus, downy mildew, Helianthus annuus.
The phylogenetic relationships of the anaerobic chytridiomycetous gut fungi (Neocallimasticaceae) and the Chytridiomycota. I. Cladistic analysis of rRNA sequences
Authors: Li Jinliang , Heath I. Brent
Published: October 2008

To clarify the phylogenetic relationships of the Chytridiomycota and the anaerobic fungi from the rumen and caecum of herbivorous animals, we analyzed the partial 18S rRNA sequences from 28 species ranging from protists to mammals and internal transcribed spacer 1 (ITS1) and its adjacent sequences from four gut fungi and one chytrid by using three algorithms from the Phylogeny Inference Package (PHYLIP). To get the confidence limits for each branch, we applied bootstrapping for each algorithm. Our analysis on partial 18S rRNA sequences shows that the Chytridiomycota are clustered with other fungi with 98, 76, and 30% confidences in the Fitch–Margoliash, neighbour-joining, and maximum parsimony algorithms. None of these three algorithms place any of 17 protists from 12 phyla with the fungi, including the chytrids. The same analysis also shows that the Spizellomycetales and Chytridiales cluster with the gut fungi but does not identify which order is closest to them. These results suggest that the Chytridiomycota, including the gut fungi, are indeed fungi but the gut fungi might not belong to the Spizellomycetales. The phylogenetic trees generated by the above three algorithms, plus the maximum likelihood algorithm, based on ITS1 and its adjacent regions show that Anaeromyces is more distant from Orpinomyces, Neocallimastix, and Piromyces. However, they failed to determine the relationships among the last three genera. Key words: Chytridiomycota, gut fungi, rumen fungi, phylogeny, rRNA sequences.
Isolation of fungal endophytes from black spruce (Picea mariana) dormant buds and needles from New Brunswick, Canada
Authors: Johnson J. A. , Whitney N. J.
Published: October 2008

Endophytic fungi were isolated from black spruce (Picea mariana (Mill.) BSP) dormant buds and needles of four age-classes. Only one isolate was obtained from 400 buds. A total of 914 isolates were obtained from the needles. With increasing needle age the rate of colonization increased between current-year and 3-year-old needles from 4 to 90%, respectively. The needle segment attached to the twig was colonized more often (p < 0.05) than other segments overall and for 6 of the 11 taxa isolated. The first endophyte from current-year needles was isolated on July 14, 1988, but endophytes were obtained from needles of the other age-classes (1, 2, and 3 years) on all sampling dates between June 10 and September 16, 1988. Key words: endophyte, Picea mariana, dormand buds, needles.
An updated interpretation of the androecium of the Fumariaceae
Authors: Decraene L. P. Ronse , Smets E. F.
Published: October 2008

A study of the floral development of Dicentra formosa, Corydalis lutea, and Hypecoum procumbens was carried out to better understand the nature of the androecium in Fumariaceae. Sepals emerge successively in a median position and are followed by two alternating pairs of petals. Four stamen primordia are formed in a diagonal position. They are promptly followed by two lateral, slightly externally inserted primordia. In Dicentra and Corydalis the stamens arise on two crescent-shaped protuberances. In Hypecoum, four diagonal androecial primordia fuse into two median staminal complexes. The gynoecium emerges as a girdling primordium with four growth centers. Different interpretations of the androecium are discussed. It is demonstrated that the androecium in the Fumariaceae consists basically of two whorls: an outer whorl of four alternipetalous stamens and an inner whorl of two lateral stamens superposed to the outer petals. The monothecal nature of the alternipetalous stamens and the fusion of the stamens in two triplets is probably caused by a spatial median compression of the flower bud. The androecium of Hypecoum is the result of interprimordial growth between the pairs of monothecal stamens, and the androecium of Pteridophyllum arises through the loss of the two lateral stamens superposed to the outer petals. Key words: Fumariaceae, floral development, androecium, stamen whorls.
Changes in species biomass in the Coastal Prairie of Texas when light and nutrients are altered
Authors: Van Auken O. W. , Bush J. K. , Diamond David D.
Published: October 2008

A 2 × 2 factorial experiment using light and nutrients as factors was carried out over 2½ years in a remnant, native Coastal Prairie of Texas. Light level, nutrient level, and date of sampling all had significant influences on total biomass, but changes were subtle, suggesting additional limiting factors. More obvious were changes in biomass of individual species, especially the dominant C4 grass species. Schizachyrium scoparium (Michx.) Nash (little bluestem), Paspalum plicatulum Michx. (brownseed paspalum), and Sorghastrum nutans (L.) Nash (Indian grass), three C4 grasses, maintained their biomass at low nutrient levels throughout the study. Sorghastrum nutans responded to higher nutrient levels with increased biomass, whereas the biomass of S. scoparium and P. plicatulum decreased. Results suggest that remnant grassland communities dominated by P. plicatum and S. scoparium are relatively stable communities maintained by yearly mowing, which removes biomass and nutrients. With the accumulation of litter, surface light levels would decrease, soil nutrients would increase, and S. nutans biomass would increase at the expense of P. plicatulum and S. scoparium. Key words: C4 grasses, fertilization, grassland, productivity, shading.
The relationship between crop size and fruit removal and its implication for the evolution of dioecy
Authors: Carr David E.
Published: October 2008

The number of fruits removed by birds from individual Ilex opaca (Aquifoliaceae) was found to increase as a function of crop size in both 1986 and 1987. The proportion of the fruit crop removed, however, was not significantly affected by crop size in either year. In 1986 the increase in relative female fitness as a function of crop size rapidly became asymptotic. In 1987 relative female fitness increased more linearly over the range of fruit crop sizes. Differences between years were attributed to differences in disperser abundance. The change in relative fitness with increasing crop size was not sufficient to explain the evolutionary stability of dioecy under conditions such as those in 1986 (i.e., asymptotic fitness gains). Under conditions of more proportional increases in relative fitness (as seen in 1987), circumstances became more favorable for the stability of dioecy, though still not sufficient. This and other empirical studies of the response of avian dispersers to variation in fruit crop size suggest that selection for increased crop size is not likely, by itself, to be strong enough to allow dioecy to exist in a stable state. I suggest that the combined effects of sexual selection (especially through male–male competition) and inbreeding depression will be more important than the effect of differential dispersal success for the evolution and maintenance of dioecy in plants. Key words: dioecy, dispersal, frugivore, holly, Ilex.
Un déterminisme architectural pour les bois de conifères à ponctuation mixte (Protopinaceae Kraüsel, 1917)?
Authors: Philippe Marc
Published: October 2008

The Mesozoic fossil wood assemblage, the Protopinaceae, have a type of pitting on the radial walls of their tracheids that is now almost extinct. Until now, the proposed explanations for this type of pitting were unsatisfactory. New observations show a connection with tree architecture, and a new hypothesis is proposed. Key words: Protopinaceae, Gymnosperms, Mesozoic, anatomy, architecture, morphology.
Water-depth tolerances of the dominant emergent macrophytes of the Delta Marsh, Manitoba
Authors: Squires Louisa , Valk A. G. Van der
Published: October 2008

The growth (shoot height, cumulative shoot length, shoot density, above- and below-ground biomass) of seven emergent species growing at five different water depths was measured for 2 years. These species belonged to three different ecological classes: (i) upper marsh species (Carex atherodes, Scolochloa festucacea, and Phragmites australis) that occupy sections of the water-depth gradient that are only seasonally flooded in the Delta Marsh; (ii) lower marsh species (Typha glauca and Scirpus lacutris spp. glaucus) that occupy permanently flooded areas; and (iii) drawdown species (Scirpus lacustris spp. validus and Scirpus maritimus) that become established temporarily during drawdowns. Upper marsh species could not adjust their shoot length if they were growing in water deeper than 20 cm. Lower marsh species were able to do this in water up to 70 cm deep. All three types survived for 1 or 2 years in water too deep for long-term persistence. Scirpus species survived as tubers in areas with water too deep for them to grow. The distributions of the seven species in the experiments overlapped considerably, and all species cooccurred at water depths to 70 cm after 2 years of flooding. The predicted distribution in the four dominant species along a water-depth gradient were consistent with their actual distributions in the Delta Marsh, but their predicted distributions overlapped much more than is the case in the field. Key words: emergent vegetation, experiment, water-depth tolerance, plant growth, distributions.