bluuebunny/crossref_metadata_2025 huggingface dataset:
Taxonomic revision of the Carex stricta (Cyperaceae) complex in eastern North America
Authors: Standley Lisa A.
Published: September 2008

Morphological studies of the Carex stricta complex confirm hypotheses based on chromosome numbers that there are three distinct species in eastern North America, Carex stricta, C. emoryi, and C. haydenii, but they do not indicate the existence of any distinct infraspecific taxa. These species are compared phenetically with all other North American species of section Phacocystis. Results indicate that the three species examined here do not form a closely related subgroup within the section as suggested by previous authors. Distribution maps, descriptions, and synonomy are provided for these species, and a complete key to the species of section Phacocystis in eastern North America is given.
Influence of volatiles from healthy and decaying sweet potato storage roots on sclerotial germination and hyphal growth of Sclerotium rolfsii
Authors: Clark C. A.
Published: September 2008

Volatiles released from sweet potato storage root tissue infected by different sweet potato storage root pathogens stimulated eruptive germination of sclerotia of Sclerotium rolfsii but did not influence the direction of hyphal growth on agarose. Volatiles from healthy sweet potato storage root tissue did not affect percent hyphal or eruptive germination of sclerotia of S. rolfsii but stimulated directional growth of hyphae toward the healthy tissue. In laboratory experiments, the frequency of infection of sweet potato stem segments by S. rolfsii on the surface of natural soil was increased when sclerotia were incubated in the presence of decaying sweet potato storage root tissue. Incidence of sclerotial blight lesions on sprouts in plant beds was increased in the presence of roots infected by Fusarium solani or Erwinia chrysanthemi. Volatiles from decaying sweet potato mother roots may predispose sweet potatoes to sclerotial blight.
Interactions of the bean rust and cowpea rust fungi with species of the Phaseolus–Vigna plant complex. II. Histological responses to infection in heat-treated and untreated leaves
Authors: Elmhirst Janice F. , Heath Michèle C.
Published: September 2008

A comparison of the histological responses of species within the Phaseolus–Vigna plant complex to single isolates of the bean and cowpea rust fungi revealed that no particular response was restricted to any plant taxonomic group, although species differed in the proportion of infection sites at which a particular response was exhibited. Related species did not always show similar frequencies of responses and sometimes there were differences between different genotypes within a nonhost species. In host and nonhost species, preinoculation heat treatment commonly inhibited prehaustorial defenses and delayed the death of the invaded cell. Growing fungal colonies subsequently developed in many species, even those considered nonhosts, particularly if they exhibited a high frequency of prehaustorial defenses in untreated leaves. It is argued that a lack of heat-induced colony formation is a sign of parasite-specific resistance, which most likely evolved only in originally susceptible plants. Consequently, the data suggest that the bean rust fungus has had a long association with American species of the complex and that extant nonhost species may have evolved from susceptible ancestors. In contrast, the cowpea rust fungus appears to have had little evolutionary contact with these American species and may not be as closely related to the bean rust fungus as originally thought.
On the petiolar structure of some Asplenium species
Authors: Khare P. K. , Shankar Rama
Published: September 2008

Petiolar characters of five species of Asplenium, viz., A. cheilosorum, A. dalhousiae, A. laciniatum, A. planicaule, and A. varians, have been investigated and their taxonomic significance is discussed. Petioles in A. varians receive a single vascular strand from the rhizome with two separate xylem strands, which during their upward course, unite to form a single xylem strand. In A. dalhousiae and A. laciniatum each petiole receives two widely separated vascular strands from the rhizome, which remain separate throughout the petiole. In A. cheilosorum and A. planicaule, the two separate vascular strands join each other within the petiole to form a single vascular strand. The shape of xylem strands in a transverse section in all the five species is distinctive.
Variation in growth rate within and among full-sib families of Douglas-fir (Pseudotsuga menziesii)
Authors: Maze Jack , Banerjee Satindranath , El-Kassaby Yousry A.
Published: September 2008

Variation in growth rate in the four uppermost lateral branches of seedlings of Pseudotsuga menziesii (Mirb.) Franco was greatest among individuals within full-sib families. These results are consistent with those from other studies on conifers indicating there is much more within- than among-intraspecific group variation. Since these seedlings were grown in a common garden, it is assumed that the among-individual variation has a genetic basis. The greatest growth rate was in seedlings produced by crossing trees that had the highest average increments of growth; the lowest growth rate was in seedlings produced by crossing trees that had the lowest average increments of growth. However, the seedlings with the lowest growth rate were similar to those produced by crosses between trees with high average increments of growth. This implies that phenotypically superior trees, as assessed in a natural situation, do not necessarily produce superior offspring in their second year of growth. The high within-family variation coupled with the ontogenetic events associated with growth rate implies a complex multigenic control of growth rate. The genetic complexity of an apparently simple developmental event such as growth in length implies that evolutionary or developmental models based on a small portion of the genome may be inadequate.
Comparison of plant community–environment relations in two estuarine marshes of northern British Columbia
Authors: Campbell Alison , Bradfield Gary E.
Published: September 2008

The Dala and Yakoun estuarine marshes in northern British Columbia were compared to evaluate similarities in species composition, plant communities, and vegetation–environment relationships. The Dala is a fjord-head marsh at the mouth of a glacially fed river with a fresh to brackish salinity regime and a 7-m tidal range. The Yakoun marsh is fed by lowland bog drainage on the Queen Charlotte Islands, has a salt to brackish salinity regime, and a 3-m tidal range. Both marshes contain similar dominant species (Carex lyngbyei, Deschampsia cespitosa, Potentilla pacifica, Triglochin maritimum), but share only about one third of the total (50) vascular species recorded. Four plant community types characterizing three main physiographic zones (low, intermediate, and high) were described at each marsh. Principal component analysis (PCA) of species composition data indicated similarities in general patterns of community organization at both marshes; however, PCA of soil chemical data indicated greater between-marsh differences, especially in intermediate and high zones. Canonical correlation analysis indicated that the Yakoun shows a closer connection between overall vegetation variation and substratum elevation, and a clearer elevational zonation of communities than the Dala. Examination of tidal regime data indicated that the Yakoun experiences steeper gradients in submergence time and flooding frequency than the Dala, thus offering an explanation for the different vegetation–elevation relationships.
Les bruyères in vitro. VIII. Évolution du pH du milieu de culture et morphogenèse de l’Erica ×darleyensis. (B) Relation entre l'absorption et les phases de la croissance rythmique
Authors: Viémont J. D. , Beaujard F.
Published: September 2008

Erica ×darleyensis grown in vitro on a medium containing nitrate presents a marked rhythmic growth. We observe an increase of the pH of the medium during plant development. The rest periods are characterized by release of small amounts of OH− (or equivalents), while during the growth period, large amounts of OH− are released into the culture medium. A relationship between root activities and rhythmic growth is recognized.
Ontogeny of Alnus rubra – Alpova diplophloeus ectomycorrhizae. I. Light microscopy and scanning electron microscopy
Authors: Massicotte H. B. , Peterson R. L. , Melville L. H.
Published: September 2008

Ectomycorrhizae synthesized between Alpova diplophloeus and Alnus rubra are of two morphological types: one with a mantle formed along the entire length of the lateral roots and the other, the clavate type, with the mantle confined to the apical portion of the laterals. The morphology of the mycorrhiza is dependent on the stage of lateral root elongation at the time of colonization by fungal hyphae. Clavate mycorrhizae form on lateral roots that have already elongated at the time of fungal colonization. Fungal hyphae interact with root hairs at the base of clavate mycorrhizae. Mantles of both types are fairly compact with few extramatrical hyphae. Hartig net hyphae, which branch profusely primarily in the radial direction, are confined to the epidermis and midway along the radial walls of the outer layer of cortical cells. Second-order lateral root primordia are initiated in the mature Hartig net zone. Cells in the outer layer of the cortex of mycorrhizal roots collapse during fixation, indicating the possible presence of a barrier in the cell wall blocking the ingress of fixative.
Effects of leaf duration, nutrient supply, and temperature on the seasonal pattern of growth and nitrogen uptake in tree seedlings in a subarctic environment
Authors: Karlsson P. S. , Nordell K. O.
Published: September 2008

The seasonal dynamics of growth and nitrogen uptake were measured in pine (Pinus sylvestris) and birch (Betula pubescens ssp. tortuosa) seedlings growing in a subarctic environment. Whole-plant dry matter accumulated at about the same rate in both species. A higher rate of early summer assimilation did occur in Pinus as revealed by the simultaneous increase in fine-root weight per unit length and leaf weight per unit area. Fine-root elongation and nitrogen uptake in Pinus preceded that in Betula. Seasonal variations in unit leaf rate and relative growth rate correlated with the prevailing temperature conditions. Pinus did not differ in phenology of growth with changes in nutrient supply while the growth and duration of foliage for Betula increased with increasing nutrient supply. Foliage growth in Pinus increased during spring but not in autumn. The temperature conditions during the growth period was important for determining the seasonal production of foliage in Betula.
Variability of vegetation in tidal marshes of Maine, U.S.A.
Authors: Jacobson Heather A. , Jacobson Jr. George L.
Published: September 2008

Systematic studies of vegetation on 18 salt marshes along the coast of Maine show that the vegetation is highly variable in species composition, species richness, and zonation pattern. Marshes with high species richness are found in relatively stable geologic settings, while unstable marshes at the base of erodible bluffs have low species richness. Species composition is influenced by freshwater input. Salt-marsh zonation varies greatly in both the number of zones present per marsh and the species assemblages within zones. With a few notable exceptions, the vegetation of salt marshes in southern Maine is similar to that of marshes in southern New England. Salt-marsh vegetation in northeastern Maine is more similar to that of marshes in the Bay of Fundy region. Key words: tidal marsh, salt marsh, Maine, vegetation, New England, Bay of Fundy.
Dynamics of the microtubular cytoskeleton in the green alga Aphanochaete magna (Chlorophyta). II. The cortical cytoskeleton, astral microtubules, and spindle during the division cycle
Authors: Segaar Peter J.
Published: September 2008

The organization and ontogeny of microtubular structures associated with cell division in the green alga Aphanochaete magna have been analyzed using indirect immunofluorescence and transmission electron microscopy. The cortical cytoskeleton lining the longitudinal cell walls in dividing apical and side branch initiating cells depolymerizes at prophase, has completely disappeared at anaphase, and starts to repolymerize in the apex of the cell at the transition of mitosis and cytokinesis. At prophase, astral microtubule systems develop from the nuclear pole associated centriole complexes, and the nucleus becomes ensheathed by centriole-interconnecting astral microtubules. The asters disappear at metaphase–anaphase, reappear at telophase, and finally depolymerize at posttelophase. A star-shaped phycoplast develops at telophase, transforms into a planar array at posttelophase, and becomes associated with the new cross wall, while the cortical cytoskeleton lining the longitudinal cell walls reforms (resulting in the coexistence of two wall-lining microtubule assemblages having different origins). Finally, the phycoplast microtubules depolymerize. The presence of astral microtubule systems at prophase in green algae is discussed and the behaviour of the cortical cytoskeleton at cell division is compared with that in other plant cell systems.
Maize leaf β-1,3-glucanase activity in relation to resistance to Exserohilum turcicum
Authors: Jondle D. J. , Coors J. G. , Duke S. H.
Published: September 2008

β-1,3-Glucanase activity was assayed over a 14-day period in leaves of three maize (Zea mays L.) near-isogenic inbred lines with differing susceptibilities to the fungal pathogen Exserohilum turcicum (Pass.) Leonard and Suggs. Crude leaf extracts of β-1,3-glucanase activity had a pH optimum of 4.5 and required a sulfhydryl reagent for maximal activity. One half of the plants of each inbred line were inoculated with race 2 of E. turcicum at the beginning of the experiment. β-1,3-Glucanase activity increased with inoculation in all isolines, but was highest 14 days after inoculation in line B37Ht2, with an allele conferring specific resistance to race 2. Isoline B37HtN, with a nonspecific allele for resistance, displayed an intermediate increase in β-1,3-glucanase activity. Susceptible line B37 had the lowest β-1,3-glucanase activity. β-1,3-Glucanase activity appeared to be induced in maize and was not a result of increased enzyme activity in the pathogen.
New species and new records of fungi that attack microscopic animals
Authors: Barron G. L.
Published: September 2008

Three species of fungi that attack microscopic animals are described as new. Verticillium coronatum (Hyphomycetes) produces conidia that have a cluster of small, apical appendages. The appendages function in attaching the conidia to the cuticle of the host nematode in the initial stages of infection. Diheterospora humicola (Hyphomycetes) was found to attack bdelloid rotifers in soil. Infection of the host is initiated by ingestion of conidia. Lagenidium oviparasiticum (Oomycetes) is an aggressive parasite of the eggs of Adineta rotifers. Zoospores of the fungus encyst on the egg shell, penetrate, and transfer their contents into the egg to initiate infection.
Seed bank populations in upland coniferous forests in central Alberta
Authors: Fyles James W.
Published: September 2008

The species composition and abundance of viable seed in organic forest floor and surface mineral soil from two high-latitude jack pine dominated and two white spruce dominated stands were determined by enumerating germinants from samples placed on moist peat-moss beds. Estimated seed density ranged from 500 to 2600 seeds/m2, representing 13 species of trees, shrubs, and forbs. About half of the species in the seed bank were present as mature plants in each stand. The high seed densities recorded are inconsistent with the previously proposed poleward decline in the abundance of buried seed. The role of buried viable seed differed among species in relation to inherent seed dispersal capabilities and seed longevity. Several species were recorded that are considered to have a very short period of viability in the soil. It is suggested that even a short residence in the seed bank may be adaptive in areas where spring burning accounts for a large proportion of the total area burned annually.
The timing of Erynia radicans resting spore germination in relation to mycosis of Choristoneura fumiferana
Authors: Perry D. F. , Fleming R. A.
Published: September 2008

Resting spores of Erynia radicans germinate after storage for over 2 months at 4 °C or by natural overwintering. Percent germination increases with spore age to a maximum of 77% after 8 months at4 °C. During this period, the temperature limits for germination changed from 8–20 °C at 3 months to 4–32 °C after 8 months at 4 °C. Germination time (mean and variance) decreases with spore age. Maximum percent germination and mean germination time decrease as poststorage temperature increases. Variance is stable from 12 to 20 °C, but increases at poststorage temperature extremes. No differences in mean germination time were found in isolates, although differences in maximum percent germination and variance in mean germination time were observed. The resting spore population responses to temperature during storage (overwintering) and at post-storage temperatures (spring and summer) act to synchronize the presence of an active inoculum with that of the insect host when conidia are most infective. Entomophthorales mycosis and epizootics occur during fifth and sixth larval instars of Choristoneura fumiferana. The timing of events in the life cycle of entomophthoralean fungi with respect to that of host populations is discussed for the spruce budworm, E. radicans, and other fungal parasite – insect systems.
Growth and sporulation of the dikaryons of the dwarf bunt fungus in wheat plants and in culture
Authors: Trione E. J. , Hess W. M. , Stockwell V. O.
Published: September 2008

In the wheat plants infected with dwarf bunt, sporulation occurs only in developing kernels. The dikaryon was isolated from infected kernels and from the rachis of infected spikes. The development of pathogenic hyphae and teliosporogenesis in vivo and in vitro is described. Ultrastructural studies indicated that in vivo teliospore primordia detach from sporogenous hyphae in the hymenium layer and develop into mature teliospores. Teliospores were borne terminally on sporogenous hyphae in vitro. Substances that stimulate hyphal branching and inhibit teliospore formation of the dikaryon were isolated from vegetative wheat tissues but not from bunt-infected spikes containing the sporulating dikaryon. The dikaryon resumed sporulation only when transferred to rich nutrient media without extracts. Extracts from infected wheat spikes containing the sporulating dikaryon induced the vegetative dikaryon to sporulate. The bioregulators involved in these phenomena were not identified. Bioactive extracts had no apparent effect on the growth of the monokaryon. A fluorochrome, mithramycin, was used to detect nuclei in monokaryotic and dikaryotic hyphae. New approaches to bunt control are discussed. Key words: Tilletia caries, Tilletia controversa, monokaryon, teliospores, bioregulators.
Water-stress tolerance and late-season organic solute accumulation in hybrid poplar
Authors: Tschaplinski T. J. , Blake T. J.
Published: September 2008

Organic solute concentrations of five hybrid poplar cultivars were compared to determine the relationship between water-stress tolerance, tissue solute concentration, and growth rate under field conditions. In the expanding foliage of the faster growing Populus deltoides Bartr. × P. balsamifera L. (Jackii 4), the saturated osmotic potential and turgor loss point osmotic potential were 0.18 MPa and 0.47 MPa lower, respectively, than in the slower growing P. deltoides × P. balsamifera (Jackii 7). The expanding foliage of Jackii 4 had higher (ca. 50%) concentrations of organic solutes, attributable mainly to salicyl alcohol, salicin, sucrose, and an unidentified compound. The coupling of high productivity and stress tolerance in Jackii 4 suggests that these may be compatible rather than competing attributes. Water-stress studies on P. deltoides Bartr. × P. nigra L. (DN 22) under greenhouse conditions demonstrated that stressed trees accumulated 4 times the soluble sugar concentrations of well-watered trees, lowering the saturated osmotic potential by 0.55 MPa and turgor loss point osmotic potential by 1.0 MPa. Leaves were the primary site of osmotic adjustment to water stress and roots showed no adjustment. The use of repeated drying cycles in planting stock may aid survival of postplanting stress in species capable of osmotic adjustment. The relationship between stress tolerance and solute concentrations in the greenhouse water-stress study paralleled that of the field study.
Water relations, photosynthetic capacity, and root/shoot partitioning of photosynthate as determinants of productivity in hybrid poplar
Authors: Tschaplinski T. J. , Blake T. J.
Published: September 2008

Physiological determinants of productivity, including net photosynthesis, root/shoot partitioning of photosynthate, and leaf retention were investigated for three Populus deltoides Bartr. × nigra L. (DN 2, DN 22, DN 15) and two P. balsamifera L. × deltoides Bartr. (Jackii 4, Jackii 7) hybrids. Performance of the different hybrids was compared under controlled greenhouse conditions and in the field. There was a 2.4-fold difference in biomass production between the faster growing DN 2 and the slower growing DN 15 after 100 days growth in the greenhouse, and a 1.5-fold difference after the 1st year's growth in the field. When coppice regrowth of the two Jackii hybrids was compared after 143 days under field conditions, the biomass production of Jackii 4 was 2.2 times that of Jackii 7 and net photosynthetic rate per unit leaf area was 50 % higher than that of Jackii 7 over most of the summer. Many physiological and morphological factors contributed to the more vigorous growth of coppice DN 2 and Jackii 4. These included vigorous initial root growth relative to shoot growth, the ability to maintain higher xylem pressure potentials, net photosynthetic rate, and transpiration rate. These factors may have delayed leaf senescence and late-season photosynthetic decline of older leaves until later in the growing season. The possible causal sequence of physiological events contributing to the difference in productivity and the use of these factors for the early selection of productive hybrids or genotypes are discussed.
Interaction of Rhizobium leguminosarum and Fusarium solani f.sp. pisi on pea affecting disease development and phytoalexin production
Authors: Chakraborty Usha , Chakraborty B. N.
Published: September 2008

Pathogenicity of Fusarium solani f.sp. pisi (F. R. Jones) Snyd. & Hans was tested on five cultivars of pea (Pisum sativum L.) under identical conditions; the fungus was more virulent on cv. Arkel and less virulent on cv. Sweet Stringless. Bacterization of seeds with Rhizobium leguminosarum biovar vicieae was highly effective in reducing the severity of root rot of pea. In vitro tests with F. solani f.sp. pisi and R. leguminosarum biovar vicieae showed no antagonistic effects on solid medium. However, growth of both microorganisms was retarded in dual culture. Phytoalexins (pisatin and 4-hydroxy-2,3,9-trimethoxypterocarpan) were isolated from both Fusarium- and Rhizobium–Fusarium-infected pea epicotyls; 4-hydroxy-2,3,9-trimethoxypterocarpan was present in a greater amount in the latter than in the former, while pisatin concentration was similar in samples from both treatments.
On tripartite Frankia–mycorrhizal associations in the Myricaceae
Authors: Berliner Ruhama , Torrey John G.
Published: September 2008

Actinomycorrhizal symbiosis was studied in Comptonia peregrina (L.) Coult. and in Myrica gale L., both of the Myricaceae. Root nodules were common in all Comptonia plants in their natural habitats and in pot cultures under greenhouse conditions. Spontaneous actinorhizal infection under greenhouse conditions differed in two native forest soils. Spontaneous mycorrhizal infection in C. peregrina and in M. gale was found neither in natural habitats nor in plants growing in native forest soils under greenhouse conditions. Comptonia peregrina and M. gale inoculated with the actinomycete Frankia, with the vesicular–arbuscular mycorrhizal fungus Glomus intraradices, or with Frankia and G. intraradices together were infected by Frankia only. The nodulated plants were significantly larger compared with unnodulated plants, and their root systems showed acetylene reduction in a bioassay for nitrogenase activity. Uninfected Comptonia plants that grew in a forest soil under greenhouse conditions developed well when watered with a complete mineral nutrient solution or with a solution that lacked phosphorus, but degenerated when watered with a solution that lacked combined nitrogen or with deionized water. Comptonia peregrina and M. gale formed cluster roots that resembled proteoid roots in the Proteaceae. In Comptonia, cluster-root formation in sand culture was common in nodulated plants as well as in unnodulated plants. In M. gale, cluster-root formation was common in nodulated plants and infrequent in unnodulated plants.
Identification of endophytic hyphae of Lophodermium piceae in tissues of green, symptomless Norway spruce needles by immunoelectron microscopy
Authors: Suske Jürgen , Acker Georg
Published: September 2008

Antiserum specific for Lophodermium piceae hyphae was obtained by absorbing a rabbit L. piceae antiserum with hyphal material of different fungal isolates. The specificity of this absorbed antiserum was tested with hyphae of endophytic fungi isolated from green, asymptomatic needles of Norway spruce (Picea abies Karst.) using the on-section immunogold labeling technique. With this specific, absorbed antiserum, a homogenous labeling was obtained with cultured hyphae of L. piceae, whereas all other spruce needle endophytes examined remained practically unlabeled. Insignificant cross-reactivity was also observed with needle tissues. The absorbed antiserum was then applied for the immunoelectron microscopical identification of L. piceae hyphae in situ in infected tissues of green, asymptomatic Norway spruce needles. The function of papillalike structures observed in infected needle mesophyll as well as the role of the hyphal sheath surrounding endophytic L. piceae hyphae are discussed in connection with the interaction between L. piceae and asymptomatic Norway spruce needles.
Retention of needles and seeds on logs in Picea sitchensis – Tsuga heterophylla forests of coastal Oregon and Washington
Authors: Harmon Mark E.
Published: September 2008

Logs are a major seedbed in Picea sitchensis – Tsuga heterophylla forests; therefore, the interception and retention of seeds on these surfaces is a potential limitation on tree recruitment. The ability of log surfaces within Picea – Tsuga forests to retain needles and seeds was studied at Cascade Head Experimental Forest, Oregon. Moss- and litter-covered surfaces retained many (48–98%) of the seeds and needles placed on them, but rotten wood, sound wood, and bark of Tsuga heterophylla, Picea sitchensis, and Pseudotsuga menziesii retained few (0–8%). Examination of logs mapped in five Picea sitchensis – Tsuga heterophylla stands in Oregon and Washington indicated a mean projected log cover of 9.9%. Thin (<5 cm) and thick (>5 cm) moss mats were the most abundant log surfaces and covered 59 and 25% of the logs, respectively. Analysis of data on seedbed coverage, retentive characteristics, and seedbed-specific seedling survival indicated approximately 1% of a seed cohort would survive the 1st year on log surfaces.
Root and shoot development of Rumex species under waterlogged conditions
Authors: Voesenek L. A. C. J. , Blom C. W. P. M. , Pouwels R. H. W.
Published: September 2008

The responses of Rumex acetosa, Rumex crispus, and Rumex palustris to different levels of waterlogging were studied in sand culture experiments. Rumex crispus and R. palustris developed new flooding-resistant roots as a response to waterlogging. The growth of these new roots caused a changed vertical distribution of the root length in these species; most root length was concentrated in the upper 10 cm of the soil. Rumex acetosa did not show significant development of flooding-resistant roots and did not change its vertical root distribution during flooding of the soil. The results of the experiments indicate that growth expressed as relative growth rate is positively correlated to the development of new flooding-resistant roots under waterlogged conditions. We concluded that R. crispus and R. palustris are more resistant to waterlogging than R. acetosa; this agrees with the distribution of these Rumex species in the field. However, waterlogging resistance is probably only one of the factors influencing differences in field location between the Rumex species.
An architectural analysis of Shepherdia canadensis and Shepherdia argentea: patterns of shoot development
Authors: Hayes P. A. , Steeves T. A. , Neal B. R.
Published: September 2008

In the context of an architectural analysis, the seasonal pattern of shoot development of Shepherdia canadensis and S. argentea (Elaeagnaceae) was examined. In both species floral bud burst was the first outward manifestation of seasonal activity. Vegetative shoots of S. canadensis expanded 3 – 5 pairs of preformed leaves during a period of 9 – 10 weeks. There was no pattern of internodal length that identified annual increments. In S. argentea, 6 – 18 pairs of leaves expanded during a period of 15 – 17 weeks, the variation being related to the extent of neoformation. There was a distinct pattern of internodal length, with a maximum in midseason, so that annual increments could be recognized subsequently. Lateral buds in S. canadensis expanded only proleptically as either short shoots or long shoots. Most had declining growth rates in the subsequent year and within 5 to 7 years had undergone abscission. In S. argentea. lateral buds expanded both sylleptically and proleptically as short shoots, long shoots, or thorns. The distribution pattern of these lateral types was related to the vigour of parent shoot growth. Some abscission of short shoots was noted. For each species a stochastic flow chart of shoot development was prepared and a computer program incorporating actual data was written that simulated shoot development for up to four generations of growth. Comparison of the two species indicates that S. argentea is more plastic in response to environmental conditions.
The impact of duration of drainage on the seed banks of northern prairie wetlands
Authors: Wienhold Carol E. , Valk A. G. van der
Published: September 2008

To determine the potential role of seed banks in the restoration of drained wetlands, the seed banks of 30 extant and 52 drained and cultivated prairie potholes were sampled in Iowa, Minnesota, and North Dakota; the potholes had been drained between 5 and 70 years ago. The midsummer vegetation of most of these potholes was also sampled. The number of species in the seed bank of a pothole declined from a mean of 12.3 in extant potholes to 7.5, 5.4, 5.0, 7.4, 3.2, and 2.1 in potholes drained up to 5, 10, 20, 30, 40, and 70 years ago, respectively. The mean total seed density of extant potholes was 3600 seeds/m2. It increased to 7000 seeds/m2 up to 5 years after drainage, but then declined rapidly to 1400, 1200, 600, 300, and 160 after up to 10, 20, 30, 40, and 70 years after drainage. Changes in both species richness and seed density with increasing duration of drainage varied from state to state. About 60% of the species present in the seed banks of extant or recently drained wetlands were not detected in wetlands that had been drained for more than 20 years. Vegetation surveys of extant and drained wetlands indicated that as many or more wetland species not detected in the seed bank were present in the vegetation, as there were wetland species in the seed bank.
Family mean correlations among fitness components in wild radish: controlling for maternal effects on seed weight
Authors: Mazer Susan J.
Published: September 2008

Qualitative estimates of genetic associations among life-history and fitness components are reported for 30 sibships (or families) in a common garden population of Raphanus raphanistrum L. (Brassicaceae: wild radish). Genetic associations are detected in a qualitative way when correlation coefficients among family means are highly significant. In this study, correlation coefficients among family means are compared with phenotypic correlation coefficients and to each other to address three questions: (i) Do strong genetic trade-offs among fitness components exist in wild radish under experimental conditions? (ii) Do qualitative estimates of genetic associations differ from phenotypic correlations? and (iii) Since seed weight is strongly phenotypically correlated with many components of plant performance and since families differ in seed weight because of strong maternal environmental (nongenetic) effects, does controlling for seed weight affect the correlations among family means? Many heritable fitness components were positively correlated among families; however, strong positive phenotypic correlation coefficients were much more common than strong positive family-mean correlation coefficients. No strong negative genetic associations were detected. The tendency for phenotypic correlations to be more positive than family mean correlations is consistent with the expectation that environmental variation generates positive correlations among characters, masking genetically based trade-offs. Partitioning out the effect of seed weight had only a small effect on the magnitude of the among-family correlation coefficients.
Lodgepole pine seed germination. I. Changes in peptidase activity in the megagametophyte and embryonic axis
Authors: Gifford David J. , Wenzel Kevin A. , Lammer Doug L.
Published: September 2008

Lodgepole pine (Pinus contorta Dougl.) germination, as indicated by radicle emergence from the seed coat, was completed 2 days after imbibition at 28 °C. By this time, the hydrolysis of the megagametophyte storage protein reserve had commenced. This was 90% complete 5 days after imbibition. Megagametophytes and embryonic axes contained two classes of peptidases: aminopeptidases that hydrolyzed amino acid β-naphthylamides, and carboxypeptidases. Cell-free extract studies showed that carboxypeptidase activity was very low in mature seed megagametophytes and embryonic axes, but increased rapidly in these tissues after radicle emergence. However, maximum rates of carboxypeptidase activity only occurred when 70% of the megagametophyte storage protein reserve had been depleted 5 days after imbibition. Thus, it was unlikely that carboxypeptidases played a significant role in the rapid mobilization of megagametophyte storage proteins. Mature seed megagametophytes contained high levels of aminopeptidase activity. Following germination this level of activity was maintained in megagametophytes and only declined when storage protein hydrolysis was almost completed, 5 days after imbibition. It is proposed that aminopeptidases are involved in the hydrolysis of megagametophyte storage proteins in the germinated lodgepole pine seed.
Lodgepole pine seed germination. II. The seed proteins and their mobilization in the megagametophyte and embryonic axis
Authors: Lammer Doug L. , Gifford David J.
Published: September 2008

Insoluble crystalloid proteins formed the major storage reserve in the mature lodgepole (Pinus contorta Dougl.) seed where they were found mainly in the megagametophyte. Smaller amounts were identified in the embryonic axis. These proteins had a subunit molecular mass in the presence of sodium dodecylsulphate of 50–55 kDa. Crystalloid subunits were heterodimers with subunit polypeptide molecular masses of 33–36 and 22–23.5 kDa. Following the emergence of the radicle from the seed coat, this reserve was rapidly mobilized in both the megagametophyte and the embryonic axis, and clearly played a major nutritional role in the germinated seed. In the megagametophyte, crystalloid protein hydrolysis appeared to involve the production of a buffer-soluble protein with a molecular mass of 34 kDa that was a heterodimer. Several soluble megagametophyte and embryonic axis proteins were identified that were also rapidly hydrolyzed following germination. These too could play a storage role. Crystalloid protein hydrolysis in the megagametophyte was not accompanied by a significant increase in the soluble megagametophyte amino acid pool. In contrast, the soluble amino acid pool of the embryonic axis increased markedly following germination. Isolated germinated embryonic axes did not show this increase. Thus, amino acids generated by crystalloid protein hydrolysis appeared to be immediately exported to the developing embryonic axis, presumably to support the many metabolic events that are occurring during its early growth.
Penetration and infection of western larch seedlings by Botrytis cinerea
Authors: Dugan Frank , Blake George M.
Published: September 2008

The fungus Botrytis cinerea Persoon (ex Fries) is an important pathogen of container-grown conifer seedlings. The examination of whole mounts and serial sections of diseased needles of western larch (Larix occidentalis Nuttall) seedlings with a light microscope confirmed that the development of fungal infection structures conforms to that observed in nonconiferous hosts. Both stomatal and cuticular penetrations were evident. Infection hyphae displayed occasional taxis toward stomata on senescent needles but not on healthy needles. The treatment of seedlings with fungicides at levels corresponding to 1 and 10% normal application rates induced no consistent changes in fungal structures.
Effets d'un choc thermique sur le métabolisme des ARN et des protéines au cours de l'embryogenèse d'une fougère aquatique, le Marsilea vestita
Authors: Kuligowski Janine , Ferrand Michèle , Chenou Éliane
Published: September 2008

A mild, 2-h cold shock treatment, from 24 to 16 °C, was applied during the different stages of Marsilea vestita embryogenesis. For each main stage (proembryo, globular embryo, and completed embryo with a bilateral symmetry), cold-induced modifications in RNA and protein synthesis were studied by autoradiography of the cells after incorporation of [5-3H]uridine and [3H]leucine. In both controls and treated specimens, proembryogenesis was characterized by a lack of transcriptional activity and no labelling was detected in the cytoplasm until the 16-cell stage. Even in the absence of de novo RNA synthesis in cooled samples, proteins necessary for the first cleavages of the embryo were being synthesized, but always at a rate lower than in the reference material. These results lead us to postulate that long-lived mRNA is stored in the cytoplasm of young embryos. Transcription, slowed down by the cold treatment, starts at the 8- to 16-cell stage and increases during the globular embryo stage. In lowered temperature conditions, transport of new RNA transcripts to the cytoplasm, which was strongly inhibited during the transition from the 16- to the 64-cell stage, appears to be less sensitive to cold shock as the embryo gets older. Our results show a difference in the response to temperature between RNA and protein synthesis. However, in both cases, sensitivity to cold temperature stress decreases with age. It is the physiological status reached by the embryo when the cold temperature stress is applied that determines the intensity of the response. [Journal translation]
Vesicular–arbuscular mycorrhizal ecology of little bluestem across a prairie–forest gradient
Authors: Benjamin Pamela K. , Anderson Roger C. , Liberta Anthony E.
Published: September 2008

Changes in little bluestem (Schizachyrium scoparium) plant cover and vesicular–arbuscular mycorrhizae (VAM) root colonization, VAM spore density, and mycorrhizal inoculum potential were examined across a gradient from open sand prairie to closed oak–hickory forest in central Illinois. Soil samples were collected randomly and from the rhizosphere of little bluestem. Significant negative rank correlations were found between tree basal area and percent aerial cover of little bluestem, VAM colonization of little bluestem roots, mycorrhizal inoculum potential, and VAM spore abundance. However, spore abundances for randomly collected and rhizosphere soil samples, VAM colonization, and mycorrhizal inoculum potential had significant positive rank correlations with little bluestem cover. Highest spore densities were associated with the open sand prairie dominated end of the gradient, with lower spore numbers being found within the closed forest. Rhizosphere and randomly collected soil samples had a decrease in VAM fungal species richness as the vegetation types approached that of a closed forest community; however, dominant VAM fungal species were present throughout the gradient. Observed relationships between colonization, mycorrhizal inoculum potential, spore abundances, and little bluestem cover suggest interdependencies between host plant and associated mycobionts and (or) similar responses to environmental factors.
Succession of fungi on wood of Avicennia alba and A. lanata in Singapore
Authors: Tan T. K. , Leong W. F. , Jones E. B. G.
Published: September 2008

Randomly collected mangrove wood and wood blocks of Avicennia alba and Avicennia lanata submerged for 60 weeks in Mandai mangrove, Singapore, were investigated for marine fungi. Very frequent species on the random samples were Halosarpheia retorquens and Lignincola laevis and on the submerged wood blocks were Didymosphaeria enalia, Lignincola laevis, Lulworthia sp. 1, Aigialus parvus, Aniptodera marina, Halocyphina villosa, and Ascomycete No. 25. The fungi growing on the wood blocks showed a pattern of succession, with L. laevis as an early colonizer, D. enalia and Lulworthia sp. 1 intermediate colonizers, and A. parvus a late colonizer. The variations in the results obtained from the two sampling methods are also discussed.
Pathological changes in the cortex of Pinus halepensis (Coniferales: Pinaceae) as related to injury by Matsucoccus josephi (Insecta: Homoptera: Margarodidae)
Authors: Liphschitz Nili , Mendel Zvi
Published: September 2008

Stems of Pinus halepensis Mill. infested by Matsucoccus josephi Bodenh. and Harpaz were examined for injury caused by the larval stage of the pest. The earliest detectable pathological changes occur in the cortical parenchyma of 3-month-old stems. Presence of one to two larvae results in flag-shaped banding of young growth due to lysis of the outer parenchyma layers. Infestation with four or more larvae per 1-cm stem segment results in its death a few weeks after the emergence of the adults. Early visible histological changes, i.e., hypertrophy of parenchyma cells, are observed in stems 10–15 months of age. High density of female scales per branchlet results in hypertrophy, high polyphenol content, lysis of the parenchyma cells, numerous radial phloem ducts, and the collapse of the cortex layers. Cortex deterioration occurs from several days to several weeks after emergence of the adult females. Wound periderm that is initiated following scale injury in infested mature stems produces an early rhytidome resulting in a cork layer that separates the nonfunctioning injured cortical cells from the living tissue. This process ends in early cracking of the outer bark, peeling of flakes, and exposure of the outer distal end of resin ducts, thus resulting in excretion of resin droplets on the bark.
Disease suppression by the ectomycorrhizal fungus Paxillus involutus: contribution of oxalic acid
Authors: Duchesne Luc C. , Ellis Brian E. , Peterson R. L.
Published: September 2008

Seedlings of Pinus resinosa Ait. grown in test tubes were inoculated with the ectomycorrhizal fungus Paxillus involutus Fr. Oxalic acid was identified as one of the ethanol-soluble fungistatic and (or) fungitoxic components of the rhizosphere after fractionation by high performance liquid chromatography, paper chromatography, and gel filtration. Simultaneous inoculation of P. resinosa seedlings with authentic oxalic acid and a spore suspension of Fusarium oxysporum f.sp. pini protected the seedlings against Fusarium root rot and decreased the sporulation of F. oxysporum in the rhizosphere when compared with controls lacking oxalic acid. Quantitation of oxalic acid showed a five fold increase in production by Pax. involutus in tubes containing P. resinosa seedlings when compared with tubes lacking seedlings. The synthesis of oxalic acid by Pax. involutus is, therefore, stimulated by P. resinosa root exudate.
Pulvinus structure and leaf abscission in cadmium-treated bean plants (Phaseolus vulgaris)
Authors: Vázquez M. D. , Poschenrieder C. , Barceló J.
Published: September 2008

The effects of a phytotoxic cadmium concentration (4.45 × 10−5 M) on the structure of primary and secondary pulvini of bean (Phaseolus vulgaris L.) leaves were studied by light and scanning electron microscopy. Pulvini were also analysed for dry weight, water content, and cadmium, calcium and potassium concentrations. Relatively high amounts of Cd accumulated in the pulvini. The Cd treatment affected Ca more intensively than K concentrations, resulting in increased K/Ca molar ratios. Increase in the density of covering, glandular, and hydathode trichomes on the pulvini and internodes was observed in Cd-treated plants. Cadmium caused premature leaf abscission. Within both primary and secondary pulvini of unifoliolate and first trifoliolate leaves, Cd induced formation of a secondary abscission zone, which involved cortical cells parallel to the vascular cylinder. Cytological alterations associated with this zone were similar to those of normal plants in which the abscission zone lies at the pulvinus–petiole junction. Results suggest that Cd probably indirectly induces the conversion to cells with the competence of abscission zone cells in the cortex of pulvini.
Light, ash, and pH effects on the germination and seedling growth of Typha latifolia (cattail)
Authors: Rivard Paul G. , Woodard Paul M.
Published: September 2008

Fire is a natural process that opens Typha latifolia L. stands by removing aboveground biomass, but little is known about how ash resulting from marsh burning affects Typha seed germination. We measured the response of T. latifolia seed to simulated pre- and post-fire effects under laboratory conditions and tested seed collected in spring for the effect of ash on seed germination and seedling morphology. Seeds were soaked for 7 days in aqueous solutions of leaf extracts, ash additions, and various pH solutions in light and dark treatments at 25 °C in vitro. In light, seed germination did not vary significantly (P < 0.01, Tukey's honestly significant difference test) among solution treatments. In darkness, seed germination was inhibited mostly by green leaf extract and yielded only 15% germination. Addition of ash to green leaf extract resulted in a germination of 40%. Solutions with pH of 4.0, 7.0, and 12.0 had no signifcant effect on germination or total plant lengths, regardless of the light treatment. Root to total plant lengths were decreased by dark treatments but not by pH. Root development was strongly inhibited by green leaf extract even with ash. Shoot growth continued with no apparent root development only in these two solutions. Three implications for marsh management of T. latifolia are proposed.