bluuebunny/crossref_metadata_2025 huggingface dataset:
The localization of active inorganic carbon transport at the plasma membrane in Chlorella ellipsoidea
Authors: Rotatore Caterina , Colman Brian
Published: December 2007

A study has been made of the capacity of whole cells and intact, photosynthetically active, isolated chloroplasts of Chlorella ellipsoidea (UTEX 20) to take up CO2 by active transport. Assays for carbonic anhydrase activity and the monitoring of CO2 uptake by cells and chloroplasts was carried out by mass spectrometry. No external carbonic anhydrase was detected in whole cells or on the outer surface of the isolated chloroplasts. Upon illumination, whole cells rapidly depleted CO2 from the medium to a level below the equilibrium CO2 concentration before maximum photosynthetic O2 evolution rates were established. Addition of bovine carbonic anhydrase resulted in the reestablishment of equilibrium CO2 concentrations, indicating that the cells were actively and selectively depleting the medium of CO2. This CO2 uptake was inhibited by 10 μM diethylstilbestrol. No such rapid depletion of CO2 was observed with isolated intact chloroplasts, although the organelles demonstrated rates of photosynthetic O2 evolution of about 60% of the parent cells. Photosynthetic rates of chloroplast suspensions exceeded the rate of CO2 supply only twofold, indicating that chloroplasts have a limited ability for HCO3− uptake. Intact cells, however, use HCO3− readily. These results indicate that the principal location of inorganic carbon transporters, both for CO2 and HCO3−, is at the plasma membrane in this alga. Key words: Chlorella ellipsoidea, CO2 transport, bicarbonate transport, chloroplasts, mass spectrometry, carbonic anhydrase.
Studies on the carbonic anhydrase activity in Synechocystis PCC6803 wild type and an acetazolamide-resistant mutant
Authors: Bedu S. , Joset F.
Published: December 2007

The problem of the role and the localization of carbonic anhydrase activity in cyanobacteria has been addressed by two approaches using strain Synechocystis PCC6803. Physiological analysis of the differential effects of carbonic anhydrase inhibitors on the entry and accumulation of CO2 in cells grown under low or high inorganic carbon concentrations and determination of carbonic anhydrase activities in cellular subfractions led to the hypothesis of the presence of two different enzymes in this strain. This conclusion is compatible with current models. Only the internal enzyme could be regulated by variations of the external inorganic carbon concentrations. A parallel analysis of a mutant of this strain resistant to the inhibitor acetazolamide supported the hypothesis of the presence of two enzymes. This clone would be selectively impaired in the carbonic anhydrase activity involved in the maintenance of the internal CO2 pool, while its transport capacity is unchanged. Key words: carbonic anhydrase, physiological role, localization, inhibitors, cyanobacteria, mutant.
Effects of nitrogen limitation on uptake of inorganic carbon and specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in green microalgae
Authors: Beardall John , Roberts Simon , Millhouse Jenny
Published: December 2007

The effects of nitrogen limitation on the characteristics of inorganic carbon-dependent O2 evolution have been examined in the green microalgae Chlorella emersonii and Gloeomonas sp. When cells were grown under 5% CO2 or air, decreasing the growth rate (increasing nitrogen limitation) caused a decrease in maximum rates of photosynthetic O2 evolution, although when expressed on a per cell basis such changes were only evident at growth rates below 0.16 day−1. Severe nitrogen limitation also caused a marked decrease in k1/2 (CO2) in light- and CO2-dependent O2 evolution. Although values for this parameter were not as low as for low CO2 grown cells with a fully induced CO2-concentrating mechanism, they were less than one-half the corresponding values from cells with the mechanism fully repressed. Nitrogen-limitation also resulted in decreases in the activity and cellular content of ribulose-1,5-bisphosphate carboxylase/oxygenase. The changes to activity and levels of this enzyme were not equivalent so the specific activity decreased dramatically between growth rates of 0.57 and 0.25 day−1. Similar effects were noted in Gloeomonas and in air-grown Chlorella. The results are discussed in relation to regulation of CO2 uptake and assimilation in microalgae. Key words: microalgae, CO2 assimilation, nitrogen limitation, Rubisco, Chlorella.
The effects of inorganic carbon and oxygen on fluorescence in the cyanobacterium Synechococcus UTEX 625
Authors: Miller Anthony G. , Espie George S. , Canvin David T.
Published: December 2007

The active transport of inorganic carbon and the accumulation of the internal pool caused quenching of chlorophyll a fluorescence both when CO2 fixation was allowed or when CO2 fixation was inhibited. Upon the addition of inorganic carbon in the presence of 240 μM oxygen the rate of change in fluorescence (or quenching) was correlated (r = 0.98) with the rate of active CO2 uptake, and the extent of quenching was correlated (r = 0.99) with the size of the internal inorganic carbon pool. Fluorescence was quenched by the fixation of inorganic carbon in the absence of oxygen but the reoxidation of QA following a flash of light was slow. In the presence of inorganic carbon, with or without the inhibition of CO2 fixation, oxygen quenched fluorescence. If CO2 fixation was inhibited, the degree of quenching depended upon the oxygen concentration with a K1/2 (O2) of about 42 μM. Below 60 μM oxygen there was a further reduction of QA following a flash of light and the reoxidation of QA was slow. Rapid reoxidation of QA following a flash of light required about 240 μM oxygen. From the response to added 3-(3,4-dichlorophenyl)-1, 1-dimethylurea, the quenching by oxygen was photochemical quenching and nonphotochemical quenching did not seem to be present. For reasons that are unknown, however, only about 80% of the quenching could be reversed with high intensity flashes of light. The photoreduction of oxygen was regulated by the presence of inorganic carbon, although fixation of CO2 was not required. The mechanism of this regulation is not known but it may be due to bicarbonate relief of electron transfer between QA and QB. Some results on measuring Fo, F′o, Fm, and F′m, in Synechococcus UTEX 625 are presented. Key words: cyanobacteria, fluorescence, oxygen photoreduction, active inorganic carbon transport.
A clarification of the Medicago polyceratia – Medicago orthoceras complex
Authors: Small Ernest , Fawzy Manal
Published: December 2007

The putative species Medicago polyceratia (L.) Trautv. occurs in northwestern Africa, Iberia, and southern France. The putative species Medicago orthoceras (Kar. & Kir.) Trautv. occurs in southwestern USSR and Asia. Although separable by geography, morphological distinction has been problematical. On the basis of studies of herbarium specimens, seven characters were found to differ significantly between the two species. The most useful of these, a previously unappreciated character, substantially discriminated the species: fruits of M. polyceratia rarely have less than 35 veins intersecting the longitudinal axis of the fruit valve, whereas those of M. orthoceras rarely have more than 35. This character also differed significantly between African and European M. polyceratia. Key words: taxonomy, Leguminosae, Medicago polyceratia, Medicago orthoceras, Trigonella.
Taxonomic significance of leaf and stem anatomy of Agalinis (Scrophulariaceae) from the U.S.A. and Canada
Authors: Canne-Hilliker Judith M. , Kampny Christine M.
Published: December 2007

Features of foliar and stem anatomy of 26 annual and 1 perennial species of North American Agalinis were examined from over 200 population samples. Several species including A. aphylla, A. densiflora, A. filicaulis, A. heterophylla, A. linifolia, A. maritima, and A. oligophylla have distinctive anatomy. Evidence from anatomy supports a reclassification of North American Agalinis at the sectional and subsectional ranks. Agalinis aphylla and A. oligophylla are allied with species of section Erectae, not section Purpureae subsection Setaceae. Agalinis edwardsiana (from section Tenuifoliae) and A. aspera (section Asperae) are most similar to members of section Purpureae subsection Pedunculares. Agalinis tenuifolia (section Tenuifoliae) is similar to species of section Purpureae subsection Purpureae. Anatomical characters range from those usually regarded as xeromorphic to those typical of hydromorphic species. However, different xeromorphic characters are present in species of sections Purpureae, Erectae, and Tenuifoliae. Species of section Purpureae subsection Setaceae have filiform, adaxially grooved leaves; species of section Erectae have narrow, short sclerenchyma-reinforced leaves and very slender stems usually having fiber bundles in their ridges. Species that we retain in section Tenuifoliae have a cylinder of sclerenchyma between the vascular tissues and the fiber-laden cortex. Key words: Agalinis, Scrophulariaceae, anatomy, systematics, taxonomy.
Physiological constraints on response by Ostrya virginiana (Betulaceae) to localized folivory
Authors: Marquis Robert J.
Published: December 2007

Individual twigs of eastern hophornbeam were experimentally defoliated at the time of spring peak herbivore abundance for this plant species. When all three leaves directly subtending developing fruits and all leaves (three to five total) from the nearest twig were removed to simulate natural folivory, there was a 25% decrease in mass of individual fruits (but not in fruit number) compared with control twigs. Lower damage of up to 50% area removal for subtending and nonsubtending leaves combined produced no significant decrease in reproductive output. Experimental defoliation had no effect on growth, reproduction, or survivorship of treatment twigs in the subsequent year. At no time during the study was natural herbivore damage high enough on individual twigs to decrease their reproductive output. These results add to the evidence that resource movement among adjacent twigs and branches of woody plants is not sufficient to compensate for localized damage. Thus, we must consider both the pattern of folivory as well as total leaf area removed to understand the effects of folivorous insects on plant growth and reproduction. Key words: folivory, Ostrya virginiana, physiological integration, plant reproduction.
A numerical taxonomic investigation of the Hordeum brevisubulatum aggregate
Authors: Baum Bernard R. , Bailey Grant
Published: December 2007

Measurements of 21 morphometric characters were carried out on 317 specimens; additional observations were made in the field in Turkey, Iran, and the People's Republic of China. Using two nonparametric clustering algorithms and various discriminant analyses followed by bootstrap validation, we infer that the following morphological species are worthy of recognition: Hordeum bogdanii; Hordeum brevisubulatum, including ssp. brevisubulatum and ssp. violaceum; Hordeum turkestanicum; and Hordeum roshevtzii. We found that H. roshevtzii is very close to H. brevisubulatum. A key to species and subspecies is provided along with comments on habitats, distribution, and synonymy. Key words: numerical taxonomy, Hordeum turkestanicum, Hordeum brevisubulatum, Hordeum roshevitzii, Hordeum bogdanii, key to species.
Resistance to Phytophthora cinnamomi in callus tissue derived from three avocado cultivars
Authors: Phillips D. , Weste G. , Hinch J. M.
Published: December 2007

Calli induced from various plant parts of avocado cultivars Topa Topa (susceptible), Duke 7 (moderately resistant), and Martin Grande (resistant) were inoculated with the root and collar rotting pathogen Phytophthora cinnamomi and examined for expression of resistance. Resistance was assessed quantitatively by measuring the rate of hyphal extension across the callus surface from the point of inoculation. Resistance in the callus tissue was associated with sparse, limited mycelial growth, in contrast to prolific, dense growth on and within susceptible callus. Rates of hyphal extension on calli of the resistant ‘Duke 7’ and ‘Martin Grande’ ranged from 1–3 mm day−1 compared with 4–7 mm day−1 on calli of ‘Topa Topa’. This difference in growth was significant (P = 0.05). This is the first report of avocado callus exhibiting resistance to P. cinnamomi and it mirrors that recorded for the whole plant for the three avocado cultivars tested. Thus, the level of resistance expressed by each cultivar appears to be innate whether the host tissue remains in an organized state or is in the form of an undifferentiated callus mass. The basis of the resistance expressed appeared to be largely physiological and (or) biochemical rather than anatomical. Assessing rates of hyphal colonization on undifferentiated callus masses in vitro may provide a new and useful assay for screening and selecting host lines in avocado resistant to P. cinnamomi. Key words: callus, avocado, in vitro, resistance, Phytophthora cinnamomi, Persea.
Labile sex expression in andromonoecious Solanum hirtum: pattern of variation in floral structure
Authors: Diggle Pamela K.
Published: December 2007

Comparison of hermaphrodite and staminate flowers of andromonoecious Solanum hirtum must consider two sources of morphological variation: variation due to differences in flower position and variation due to conditions that affect sex expression. In S. hirtum, positional variation occurs among hermaphrodite flowers of unpollinated plants; flowers vary quantitatively but not functionally with position on the inflorescence. On inflorescences of pollinated, fruit-bearing plants, flowers vary both quantitatively and functionally with position such that flowers borne distally are functionally staminate. Corolla, anther, style, and ovary length of staminate flowers are significantly smaller than those of hermaphrodite flowers and they have fewer, smaller ovules. Failure of fruit set in staminate flowers is due to a combination of factors. Stigmas and styles of staminate flowers are reduced and appear to lack the secretions necessary for normal pollen germination and growth. In the ovules, the integumentary tapetum is collapsed and appears senescent and most megagametophytes are abnormal. Lack of pollen tube growth and abnormal ovules could both contribute to gynoecial sterility in staminate flowers. Key words: andromonoecy, floral structure, reproductive anatomy, sex expression, Solanum.
Visualization, adhesiveness, and cytochemistry of the extracellular matrix produced by urediniospore germ tubes of Puccinia sorghi
Authors: Chaubal Rajendra , Wilmot V. A. , Wynn Willard K.
Published: December 2007

Adherence of germinating urediniospores of the common maize rust fungus (Puccinia sorghi Schw.) to substrata was studied by ultrastructural and cytochemical examination of extracellular matrix produced by germ tubes in conjunction with measurements of adhesion to plastic and glass surfaces. Copious amounts of extracellular matrix on germ tubes could consistently be visualized by scanning and transmission electron microscopy only when (i) a cationic detergent (cetylpyridinium chloride, polydiallyldimethylammonium chloride) or a cationic stain (ruthenium red, alcian blue, cuprolinic blue) was added to the fixation solutions, (ii) germ tubes were fixed by rapid-freezing and freeze-substitution and observed with a scanning electron microscope, or when (iii) germ tubes were observed in a frozen-hydrated state by low-temperature scanning electron microscopy. Incubation of germinated spores with dilute alkalies (NaOH, KOH), pronase E (nonspecific protease), and laminarinase (β-1,3 (1,3; 1,4-glucanase) removed the extracellular matrix and detached germ tubes from surfaces. Treatments with water, dilute acids, ionic and neutral detergents, organic solvents, hydrocarbons, and several polysaccharide-degrading enzymes did not remove the extracellular matrix and also did not detach germ tubes. These results, together with staining patterns obtained with lectins and other polysaccharide-specific reagents, indicate that the extracellular matrix is composed mainly of glycoproteins rich in acidic amino acids and β-1,3-glucan polymers, and that it is probably responsible for the adhesion of the rust germ tubes to the host leaf surfaces. Key words: Puccinia sorghi, germ tube adhesion, extracellular matrix, cytochemistry.
Barrier zone formation in host and nonhost trees inoculated with Ophiostoma ulmi. I. Anatomy and histochemistry
Authors: Rioux Danny , Ouellette G. B.
Published: December 2007

Barrier zone formation was studied in small branches of Ulmus americana L., Prunus pensylvanica L.f., and Populus balsamifera L. following inoculation with Ophiostoma ulmi (Buism.) Nannf. (the Dutch elm disease pathogen). Barrier zones were continuous in the nonhosts whereas they were generally discontinuous in U. americana; barrier zone formation also occurred at a later stage of infection in the latter than in the former. Barrier zones were formed of parenchyma cells and fibers in U. americana, mainly of parenchyma cells in Prunus pensylvanica, and of fibers in Populus balsamifera. Fibers as a principal component of barrier zones are described for the first time. Histochemical tests revealed that the proportion of lignin was higher in barrier zone cell walls than in elements of the noninvaded xylem. Barrier zones contained suberized cells, the number of which was progressively greater in the order U. americana, Prunus pensylvanica, and Populus balsamifera. However, many fibers of U. americana occasionally formed a continuous barrier zone and had an internal layer that was slightly suberized. In addition, phenolic compounds were usually detected within barrier zone cells of these species. Key words: Dutch elm disease, nonhost plants, Ophiostoma ulmi, Ulmus americana, anatomy, histochemistry.
Control of seedling emergence by ground cover: a potential mechanism involving seed predation
Authors: Reader R. J.
Published: December 2007

The presence of ground cover (i.e., plant biomass and litter) could restrict seedling emergence by providing a habitat for seed predators. To test this hypothesis, a field experiment was conducted with three old-field forbs (Daucus carota, Centaurea nigra, Taraxacum officinale). Ground cover was either removed or left in place and sown seeds of the three forbs were either protected from predators or left unprotected. Where seeds were protected from predators, seedling emergence did not improve when ground cover was removed. Where seeds were not protected from seed predators, seedling emergence did improve significantly for all three species when ground cover was removed. Apparently, seed predators removed more unprotected seeds where ground cover was present than absent, thereby reducing seedling emergence. These results are consistent with the hypothesis that ground cover could restrict seedling emergence by providing a habitat for seed predators. Key words: old field, seedling emergence, seed predation.
Selection for mating competence in Magnaporthe grisea pathogenic to rice
Authors: Chao Chih-Cheng T. , Ellingboe Albert H.
Published: December 2007

Sib selection for mating competence among isolates of Magnaporthe grisea that are pathogenic on rice has led to the selection of isolates where the mating type alleles are the only restriction on mating competence. Isolates are able to mate with all sibling isolates of opposite mating type and produce asci with ascospores. Isolates can function as male, female, or hermaphrodite in mating depending on the isolates with which they are mated. Mating competence is controlled by the genes in both mated isolates. Key words: mating competence, sib selection, rice blast, genetics.
A histological and elemental analysis study of the mature seed of Begonia semperflorens
Authors: West M. M. , Lott J. N. A.
Published: December 2007

The total element content and the subcellular distribution of mineral nutrients were investigated in a species that has very minute seeds. The major storage substances in the seed of Begonia semperflorens were lipids sequestered in lipid vesicles and proteins concentrated in protein bodies. Transmission electron microscopy revealed the presence of protein crystalloids and electron-dense globoid crystals in the protein bodies. These inclusions varied both in size and number in protein bodies from different tissues. Energy dispersive X-ray analysis of the globoid crystals showed the high Mg, K, and P levels characteristically found in phytin from large-sized seeds. Small traces of Ca were found in globoid crystals within protein bodies found in the provascular tissue of the embryo. Neutron activation analysis was used to measure the elemental composition of the whole seed and these results were correlated with the findings of energy dispersive X-ray analysis studies of globoid crystals. Key words: Begonia seed, energy dispersive X-ray analysis, protein body, globoid crystal, protein crystalloid, neutron activation analysis.
The number and distribution of incompatibility factors in natural populations of Pleurotus ostreatus and Pleurotus sapidus
Authors: Anderson Neil A. , Furnier Glenn R. , Wang Andrew S. , Schwandt John W.
Published: December 2007

Pairings of single-spore isolates from different basidiocarps were made to examine the numbers and distributions of incompatibility factors in the tetrapolar basidiomycetes Pleurotus ostreatus and Pleurotus sapidus. These factors do not appear to be randomly distributed, with multiple basidiocarps on a single tree or log arising from a single mycelium, multiple basidiocarps on a single tree or log sharing a single common monokaryotic parent, and a tendency toward spatial clustering of factors even when multiple basidiocarps from the same tree or log are excluded from the analyses. For one 30-km2 collection area, the estimated numbers of A and B factors in the P. ostreatus population were 126 and 354, respectively, yielding an estimated outbreeding efficiency of 0.99. Estimated outbreeding efficiencies were quite high [Formula: see text] even in a sample taken from a very small area (0.09 m2), illustrating the ability of the tetrapolar mating system to simultaneously prevent self mating and minimize the number of incompatible matings. Key words: Basidiomycotina, fungi, mating system, population genetics.
Ultrastructure of mitosis in the algal parasitic fungus Polyphagus euglenae
Authors: Roychoudhury Sonali , Powell Martha J.
Published: December 2007

Ultrastructure of mitosis in the parasitic fungus, Polyphagus euglenae, was investigated with emphasis on centrosome structure and prophase events. The interphase centrosome included a diplosome, scattered electron-dense satellites, and multiple ring-shaped microtubule foci. As centrosomes separated during prophase, microtubular arrays extended between the replicated centrosomes and radiated out along the outer surface of the nuclear envelope. The asymmetric configuration of these microtubular arrays suggests that intersecting microtubules provide tension forces on elongating centrosome to centrosome microtubules during centrosome separation. After centrosome migration, multiple microtubule foci appeared to fuse into crescent-shaped microtubule organizing centers. Condensing chromatin was concentrated in the region of the future equatorial plane of the mitotic spindle prior to the appearance of discontinuities in the nuclear envelope and incursion of the spindle. The nucleolus fragmented during prometaphase, and fragments were discarded with the interzonal region during telophase. Nucleoli appeared in daughter nuclei before chromatin became diffuse. Similarities in the mitotic apparatus of P. euglenae with that previously reported for Monoblepharella sp. support a phylogenetic affinity between members of the orders Chytridiales and Monoblepharidales. Key words: mitosis, Polyphagus euglenae, Chytridiales, centrosomes, phylogeny, ultrastructure.
Substrate control of litter decomposition in four Rocky Mountain coniferous forests
Authors: Taylor B. R. , Prescott C. E. , Parsons W. J. F. , Parkinson D.
Published: December 2007

The influence of chemical and physical quality of litter on its rate of decomposition was examined by measuring mass loss from 19 diverse litter types, including leaves, needles, forbs, wood, and roots in the Kananaskis Valley of Alberta, Canada. Litter samples drawn from three adjacent forests of lodgepole pine, white spruce, and Engelmann spruce – subalpine fir, and from a small clearcut area, were allowed to decompose for 3 years at their sites of origin. The best predictors of mass loss were the initial concentrations of lignin and labile material in the litter. Adding N or P contents as a second term, rather than as a lignin to nutrient ratio, significantly improved mass loss predictions. There were abrupt limits for the influence of lignin (above 28%) and N (below C:N of 30:1); similar limits were observed for all predictors except labile content. None of these chemical parameters, nor a physical measure, particle diameter, were useful in predicting rates of decomposition of high-lignin, woody substrates. The relative importance of the various litter quality parameters in determining rates of mass loss in the clear-cut area was very similar to that in the forests, despite considerably more rapid decomposition in the clearcut. Key words: decomposition, lignin, litter, nutrients, Rocky Mountains, wood.
Shoot initiation on a Graptopetalum leaf: sequential scanning electron microscopic analysis for epidermal division patterns and quantitation of surface growth (kinematics)
Authors: Tiwari Suresh C. , Green Paul B.
Published: December 2007

A non destructive mold and cast procedure allows repeated imaging of growing plant surfaces by scanning electron microscopy. Individual cells and their clonal progeny can be recognized in succesive images. This allows comprehensive analysis of cell lineage on the epidermis. It also provides data for the quantitative characterization of surface growth (kinematics). The technique and both types of analysis were applied to a small meristematic surface of a Graptopetalum leaf as it develops from a flat field of parallel cell files into a stem and leaves, all with radial symmetry. New organ surfaces formed from groups of cells that were not clones of the cells initially present. Hence cell image was not important. In the revision of symmetry some regions retain the original cell file polarity, others change it by 90°. Areas that do not change have mainly transverse anticlinal divisions. Areas that change maximally show repeated longitudinal divisions to make a rib meristem pattern with new cross walls normal to the direction of future growth. Growth direction soon changes. This occurs in regions known to undergo a 90° shift in cellulose reinforcement direction. It is concluded that distinctive anticlinal division behavior accompanies lateral formation and may be significant in the mechanism. Key words: anticlinal divisions, Graptopetalum, kinematics, morphogenesis, shoot initiation, sequential scanning electron microscopy.
The response of juvenile and small adult western juniper (Juniperus occidentalis) to nitrate and ammonium fertilization
Authors: Miller P. M. , Eddleman L. E. , Miller J. M.
Published: December 2007

Effects of nitrate-N and ammonium-N fertilization on foliar nitrogen concentrations, carbon dioxide assimilation, leaf conductance, transpiration, intercellular carbon dioxide, xylem pressure potentials, specific leaf mass, and growth were measured on naturally established juvenile and small adult Juniperus occidentalis growing in central Oregon where ammonium-N was the dominant form of soil nitrogen throughout the summer. Fertilization with both forms of nitrogen increased foliar nitrogen concentrations in juveniles and small adults in May; concentrations in small adult foliage from the nitrate-N treatment were still higher than controls in September. Both forms of nitrogen reduced carbon dioxide assimilation and potential photosynthetic nitrogen-use efficiency. The negative relationship between nitrogen addition and carbon dioxide assimilation was more apparent in juveniles than in small adults; negative effects were more pronounced in the ammonium-N treatment than in the nitrate-N treatment. Leaf conductance and transpiration were also reduced, but reductions of water loss were greater than were negative effects of fertilization on carbon gain; thus water-use efficiency of juvenile and small adults increased in May and July. The depression in gas exchange processes was detectable for a longer period during the summer in juveniles than in small adult J. occidentalis. Branchlet elongation of juvenile and small adult J. occidentalis was increased with nitrate-N and ammonium-N addition, but variability reduced significance levels. Juniperus occidentalis appears to be adapted to utilize low, ambient levels of soil nitrate at the research site and did not preferentially utilize ammonium. Key words: gas exchange, water relations, foliar nitrogen, growth.
Isozyme structure of Peridermium harknessii in the western United States
Authors: Vogler D. R. , Kinloch Jr. B. B. , Cobb Jr. F. W. , Popenuck T. L.
Published: December 2007

We conducted a population genetic study of the western gall rust fungus (Peridermium harknessii) using isozymes as genetic markers. Electrophoresis of 341 single-gall aeciospore isolates collected from several pine species revealed that western gall rust is comprised of two distinct zymodemes (multilocus electrophoretic types) in the western United States. Within zymodemes, all 15 loci studied were monomorphic (0.95 criterion), although variants were found at low frequencies (≤ 0.03) at 3 loci. Zymodeme I was characterized by single bands, indicating homozygosity at all loci; it consisted of isolates from all pine species and environments studied, including the Pacific Coast and Cascade Ranges and the Sierra Nevada and Rocky Mountains. Zymodeme II, which was absent from coastal forests, was characterized by double or triple bands at 6 of 15 loci. The additional bands were interpreted as products of alternative alleles in heterozygous condition; isozyme phenotypes at the other nine loci were identical to those of zymodeme I. Presumed heterozygotes were fixed within zymodeme II, and homozygotes of alleles unique to this zymodeme were not found. Generally, all isolates sampled from a forest stand were in the same zymodeme, and when isolates from both zymodemes were found in the same location, recombinant genotypes between zymodemes were not observed. Such extreme disequilibrium is inconsistent with sexual reproduction, indicating that P. harknessii is asexual. Key words: western gall rust, Pinus spp., genetic variation.
Patterns of allozyme variation in tamarack (Larix laricina) from northern Ontario
Authors: Liu Zhaowei , Knowles Peggy
Published: December 2007

Rooted cuttings from approximately 26 trees (range 9–37) from each of 44 populations of tamarack (Larix laricina (Du Roi) K. Koch) in northern Ontario were analyzed electrophoretically for allozyme variation in 13 enzyme systems coded by 18 loci. A low level of variability relative to many other conifers was found, with expected and observed heterozygosity per population of 0.104 and 0.096, respectively, χ2 tests for allelic homogeneity among populations indicated heterogeneity (α = 0.05) at four loci. Approximately 2% of the total genetic diversity occurred among populations, with the remainder (98%) residing within populations. The mean genetic distance over all pairs of tamarack populations was 0.0025. Four methods of cluster analysis based on genetic distances and a discriminant function analysis of the genotypic structure of the populations revealed no consistent patterns of variation relative to geographic location, although one of the clustering procedures showed a weak east–west pattern. The results indicate that (i) the level of variation in these populations of tamarack is substantially less than that previously reported for its range-wide distribution; (ii) the population structure of tamarack is consistent with that of other conifers, indicating little deviation from Hardy–Weinberg expected genotypic frequencies and low levels of differentiation; and (iii) the distribution of the variation provides little evidence to support the model of two routes of tamarack post glacial reinvasion meeting west of Lake Superior. Key words: tamarack, eastern larch, Larix laricina, allozyme, isozyme, population, genetic variation, northern Ontario.
Interactions between Sclerotinia sclerotiorum and Epicoccum purpurascens
Authors: Zhou Ting , Reeleder R. D. , Sparace S. A.
Published: December 2007

Sterile culture filtrates of Epicoccum purpurascens decreased severity of white mold of bean and increased pod yield when applied prior to inoculation of beans with Sclerotinia sclerotiorum. Extracts of these culture filtrates inhibited ascospore germination and mycelial growth of S. sclerotiorum. Similar inhibition of hyphal growth of S. sclerotiorum occurred when dual cultured with E. purpurascens. Contact and penetration of hyphae of S. sclerotiorum by hyphae of E. purpurascens occurred rarely on agar-covered slides and was not observed on flower petals. Inhibition of ascospore germination and germ-tube elongation occurred on agar-covered slides where E. purpurascens had been grown previously; however, addition of nutrients decreased inhibition. Colonization of bean flowers by E. purpurascens reduced white mold incidence. The degree of disease control was affected by addition of nutrients and whether or not colonized flowers were autoclaved. Key words: antifungal compounds, competition, biological control, white mold, Phaseolus.
Occurrence of pseudopodial abstriction in the aphanoplasmodium of Stemonitis flavogenita (Myxomycetes, Stemonitales)
Authors: Haskins E. F.
Published: December 2007

The first photographic evidence is presented of the derivation of uninucleate, amoeboid cells from aphanoplasmodia of Stemonitis flavogenita. This process, observed only in young plasmodia, involves the abstriction of aphanoplasmodial pseudopodia. The biological ramifications of this phenomenon are discussed. Key words: Stemonitis, Myxomycetes, pseudopodial abstriction, plasmodial to uninucleate amoeboid cell conversion.
Ultrastructural study of ascoma and ascospore development in Ophiostoma distortum and Ophiostoma minus
Authors: Wyk P. W. J. van , Wingfield M. J.
Published: December 2007

The development of the ascoma, ascus, and elongated ascospores in Ophiostoma distortum and Ophiostoma minus was studied at the ultrastructural level and compared with that of other related Ascomycetes. The organization of the centra in O. distortum and O. minus differed considerably. In O. distortum, asci were irregularly arranged in clusters that occurred in the lower half along the periphery of the ascoma. In O. minus, asci developed from a central cluster at the base of the ascoma. The asci extended upwards and outwards from the base. Ascospore development in both fungi commenced with the formation of double, delimiting membranes in the ascus. Between these membranes ascospore walls developed, consisting of the primary and secondary wall. In comparison with other species having similar ascospores, differences were found between the number of wall layers of the ascospores and formation of the outer wall layers. The secondary wall and perisporic sac of O. minus were smooth and of uniform thickness, whereas the inner layer of the secondary wall in O. distortum was thickened and distorted in certain areas. It is suggested that additional ultrastructural studies should be undertaken to provide a better understanding of the development and evolution of ascospore sheaths in Ceratocystis sensu lato. Key words: Ceratocystis, elongated ascospores, centrum.
Pollination in an understorey vine, Smilax rotundifolia, a threatened plant of the Carolinian forests in Canada
Authors: Kevan Peter G. , Ambrose John D. , Kemp James R.
Published: December 2007

Round-leaved greenbrier, Smilax rotundifolia L. (Liliaceae), is an insect-pollinated, dioecious, understorey vine. Its pollen is linked by viscin threads, effectively preventing wind dispersal. In most sites populations are not sexually reproductive, being unisexual, but do not spread vegetatively. Where both sexes occur, fruits and seeds are produced naturally. Artificial cross-pollinations can enhance the level of fruit and seed set. Understanding the biology of this threatened species is important for habitat management and conservation. Key words: dioecy, greenbrier, viscin, floral form, conservation, pollination.
Pollen morphology of the Rosaceae of western Canada. IV. Luetkea, Oemleria, Physocarpus, Prunus
Authors: Hebda R. J. , Chinnappa C. C. , Smith B. M.
Published: December 2007

Pollen grains of 12 species of western Canadian rosaceous genera, Luetkea, Oemleria, Physocarpus, and Prunus, were studied in the light microscope and scanning electron microscope. All pollen grains are produced as isopolar, radially symmetrical, usually tricolporate monads. Grains are predominantly spheroidal with a circular to triangular amb. Most of the species exhibit a well-developed chambered aperture complex at the equator, formed by a pair of sexinal flaps whereas in Prunus spinosa, Prunus americana, and Prunus virginiana the chamber is absent or weakly developed. Oemleria cerasiformis has no pore flaps. Apertures of Prunus emarginata and Prunus virginiana often have an equatorial bridge over the aperture complex. The exine of Prunus, Physocarpus, and Luetkea pollen is tectate perforate, like that of many Rosaceae. Sculpturing consists of ridges and valleys that form a striate to rugulate pattern. Ridges and valleys tend to be mainly parallel to the colpus but often loop near the poles. Pollen grains of Prunus spinosa are always rugulate or vermiculate with ridges arranged randomly. Oemleria cerasiformis pollen appears tectate imperforate. Ridges and valleys intersect at triple points in the subpolar region and curve in a semicircle around the pore area. On this basis Oemleria pollen is distinct from all other western Canadian Rosaceae. Pollen grain size ranges from small for Luetkea pectinata (17 μm in diameter) to medium for Prunus spinosa (36 × 33 μm). Key words: pollen morphology, Rosaceae, Western Canada, systematics.
Wild beets as an important inoculum source of Alternaria alternata, a cause of leaf blight of cotton in Israel
Authors: Bashan Yoav , Levanony Hanna , Or Reuven
Published: December 2007

Alternaria alternata, isolated from the leaves of wild beets, infected cotton as well as wild and cultivated beets. Scanning electron microscopy of wild beet and cotton leaves infected by an aggressive isolate of A. alternata revealed that conidiophores of the pathogen emerged only from necrotic areas of leaf tissues. Sporulation occurred on leaves only during periods of high relative humidity (> 95%) and temperatures ranging from 20 to 28 °C. Under low relative humidity (60% at 22–25 °C), mycelium penetrated into internal tissues of the leaf or emerged through the stomata. A less virulent isolate did not develop surface mycelium on inoculated leaves, but sporulation was detected on the leaf veins. Plants in several cotton fields adjacent to the diseased wild beet plants were infected by the pathogen early in the growing season. This study proposes that isolates of A. alternata that are virulent on cotton may overwinter on wild beet plants, making them an important source of the pathogen inoculum in epidemics of alternaria blight of cotton. Key words: Alternaria, beet, cotton diseases, fungi overseason transfer, fungi overwintering, survival.
Effects of simulated acidic rain on upper leaf surface of Zea mays foliage
Authors: Knittel R. , Pell E. J.
Published: December 2007

Experiments were conducted to determine the histological effects of simulated acidic rain on the cuticle of Zea mays L. cv. B73 × Mo 17 and to ascertain whether subsequent drought stress might elicit interacting effects. Greenhouse-grown plants were treated twice weekly with simulated acidic rain of pH 5.0 or 3.0 for 3–4 weeks. Half of the plants in each pH treatment were then subjected to a 10-day drought stress by withholding water, while the remaining plants continued to receive rain treatments. At the end of the treatment period, leaf tissue was sampled and fixed for light or scanning electron microscopy. Small elongated white lesions approximately 1 mm in diameter appeared in a random pattern on leaves 5–7 that were treated with rain of pH 3.0 for 3 weeks. Plants treated with rain of pH 5.0 did not exhibit these lesions. Lesions were clearly defined areas of collapsed necrotic tissue extending through the leaf. Within lesions, the basal region of 50% of the trichomes had collapsed bases in confluence with adjacent cells. Epicuticular morphology was unaffected by simulated acidic rain or drought stress and appeared as a crystalline platelet-like formation. From our observations, it appeared that factors that maximized droplet retention or droplet deposition, e.g., leaf wettability and leaf orientation, maximized lesion formation. Drought stress had no observable influence on the cuticle of plants treated with either simulated acidic rain treatment. Key words: corn, acid rain, drought stress, histology, cuticle, transpiration.
Morphology and distribution of species in the Medicago murex complex
Authors: Gillespie D. J. , McComb J. A.
Published: December 2007

Morphological, cytological, and agronomic characteristics are reported for 560 accessions of the Medicago murex Willd. complex collected from countries bordering the Mediterranean and grown in field plots in Western Australia. All plants of the 2n = 16 taxon were shown to have white flecks on the leaves, a mean number of florets on each peduncle of < 2.5, and usually no ridges on the edge of the pod coils. Plants of the 2n = 14 taxon never had white leaf flecks, 99% of accessions had a mean number of florets > 2.5, and most had three distinct ridges on the pod coils. Plants of the two taxa were equally vigorous and both were widespread, occurring sympatrically in many Mediterranean countries. The 2n = 16 and 2n = 14 taxa do not cross and should be recognized as separate species. A reexamination showed that Willdenow's original material of M. murex was most likely to be of the 2n = 16 species. We suggest that the name of the 2n = 14 species is Medicago sphaerocarpos Bertol. Key words: Medicago murex, Medicago lesinsii, Medicago heterocarpa, taxonomy, distribution, speciation.
Cost of seed versus rhizome production in Agropyron repens
Authors: Reekie E. G.
Published: December 2007

I examined growth and allocation patterns in genotypes of Agropyron repens isolated from six habitats that differed in disturbance frequency. The trade-off between seed and rhizome production and between either mode of propagation and growth of leaves, stems, and roots was determined by calculating both within- and among-genotype correlations between functions. I also examined how level of light and nitrogen availability affected these trade-offs. Large differences were found among populations in how resources were divided between infructescences and rhizomes, but there was no evidence of a direct trade-off. Regardless of environment, or level at which correlations were examined, there was never a negative correlation between seed and rhizome production. Depending on level of nitrogen and light availability, there was usually a trade-off between seed or rhizome production and growth of leaves, stems, and roots. The two modes of propagation differed in how they responded to resource availability such that their relative cost varied among environments. I suggest differences among populations in allocation to seed versus rhizome production are due to these differences in cost. When cost of seed production is high relative to rhizome production, allocation to rhizome is favored. Conversely, when cost of rhizome production is high relative to seed production, allocation to infructescences is favored. Key words: vegetative reproduction, sexual reproduction, allocation, disturbance, reproductive cost, resource availability, clonal growth.
Gas exchange processes of yellow-cedar (Chamaecyparis nootkatensis) in response to environmental variables
Authors: Grossnickle Steven C. , Russell John H.
Published: December 2007

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) gas exchange processes were measured in response to the following primary environmental variables: photosynthetically active radiation, vapour pressure deficit, root temperature, and soil moisture. Under nonlimiting edaphic conditions, maximum stomatal conductance and maximum CO2 assimilation increased rapidly as photosynthetically active radiation increased from 0 to 200 μmol∙m−2∙s−1 and from 0 to 500 μmol∙m−2∙s−1, respectively. Thereafter, greater photosynthetically active radiation levels only resulted in minor increases in stomatal conductance and CO2 assimilation. Maximum stomatal conductance and maximum CO2 assimilation declined in a concave manner as vapour pressure deficit increased from 1 to 5 kPa. Response surface model for stomatal conductance showed vapour pressure deficit was the primary influence after light had caused initial stomatal opening. Response surface modeling approach showed CO2 assimilation increased as photosynthetically active radiation increased, but increased vapour pressure deficit resulted in a suppression of CO2 assimilation. Response surface model showed internal CO2 concentration declined sharply as photosynthetically active radiation increased from 0 to 500 μmol∙m−2∙s−1, but it remained constant with increasing vapour pressure deficit. Decreasing root temperature resulted in a continual decline in CO2 assimilation and stomatal conductance from 22 to 1 °C, while internal CO2 concentration declined from 22 to 13 °C with little change between 13 and 1 °C. As predawn shoot water potential decreased from −0.5 to −2.0 MPa, CO2 assimilation declined in a linear manner, while stomatal conductance and internal CO2 concentration declined in a concave manner. Key words: Chamaecyparis nootkatensis, CO2 assimilation, stomatal conductance, internal CO2 concentration, photosynthetically active radiation, vapour pressure deficit, root temperature, predawn shoot water potential.
Effects of stand density on outcrossing rate in two Norway spruce (Picea abies) populations
Authors: Morgante M. , Vendramin G. G. , Rossi P.
Published: December 2007

The mating system was investigated in two neighbouring Norway spruce (Picea abies (L.) Karst.) populations with markedly different stand densities. The amount of outcrossing was estimated using open-pollinated array data at four enzyme loci. Multilocus estimates of the proportion of viable progeny owing to outcrossing were 0.956 and 0.955 for the low- and high-density stand, respectively, indicating that the large reduction in stand density had no impact on outcrossing rates. The multilocus estimate was higher than the mean single-locus estimate only for the low-density stand. The lowering of the mean estimate in the low-density stand is probably a consequence of the clustering of related individuals. The regression of pollen allele frequencies on ovule genotype, which is a direct measure of the effective selfing caused by consanguineous matings, had a significant coefficient for the low-density stand and a nonsignificant one for the high-density stand. This obvservation confirms that the major effect of low-stand density in Norway spruce is the occurrence of consanguineous matings. Key words: mating system, outcrossing rate, inbreeding, Norway spruce, stand density.