摘要:

The majority of papers dealing with environmental correlates of phenotypic variability are concerned with macrogeographical structuring of the investigated species. However, a possible major component of phenotypic differentiation in some taxa is small-scale variability in the microenvironment. The statistical methods usually employed for such studies seems to be restricted to a few standardized sets of procedure, often assuming linearity and additivity of effects among variates. In this paper we studied small-scale geographical differentiation of phenotypes ofCapsella bursa-pastoris(Cruciferae), a species characterized by an apparent extreme degree of phenetic specialization that could be due to fixation of alternative alleles in small local demes. We use nonparametric multivariate procedures to test the relationships between phenotypic principal components, geographic distance, and a number of microenvironmental parameters. A concept recently applied to population genetics, that of biological boundaries, is used here in relation to phenetic variation to assess its association with geographical mapping of the populations studied.Key words:Capsella, Mantel test, phenotypic boundaries, biotic parameters, principal components analysis.

ISSN:0008-4026    

DOI:10.1139/b91-207

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Bean leaves inoculated 24 h previously with the bean rust fungus were inoculated with spores ofCochliobolus heterostrophus,Stemphylium sarcinaeforme,Stemphylium botryosum, orCladosporium fulvum. For all species exceptC.fulvum, hyphal growth resulting from stomatal penetrations was greater than that in leaves that were not rust-infected but did not continue for more than about 24 h. The incidence of direct penetrations for these three fungi also was increased by prior rust infection, and the incidence of epidermal wall appositions was reduced. Growth ofC.fulvumin rust-infected leaves only exceeded that in control leaves when spores were injected into the intercellular spaces of the mesophyll tissue. Rust infection either had little effect on the incidence of cell death, normally induced by all of the tested fungi exceptC.fulvum, or it enhanced this response in association with greater fungal growth. From this and previous studies, it seems that successful rust infection increases the growth of a wider array of fungi nonparasitic to beans than treatments with growth regulators or intercellular washing fluids from rusted tissue. Its effect is most closely mimicked by preinoculation treatments with heat or protein synthesis inhibitors, but it does not induce indiscriminate susceptibility. Its effect may, in part, be due to the suppression of defenses involving wall modifications.Key words:Uromyces appendiculatus, induced susceptibility, nonhost resistance.

ISSN:0008-4026    

DOI:10.1139/b91-208

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

We examined the effect of water stress on leaf demography in four grass species known to differ in degree of drought resistance. Stress was imposed by growing plants in solution culture and lowering water potential of the solution either slowly, or rapidly, by the addition of polyethylene glycol. Rapid stress reduced the number of leaves by increasing leaf death rate and decreasing birth rate. Gradual stress reduced the number of leaves by temporarily decreasing leaf birth rate; death rate also decreased, partially compensating for the reduction in birth rate. Death rates were age specific; rapid stress had little effect on young leaves, and gradual stress increased leaf longevity to the greatest extent in those leaves that emerged immediately prior to the imposition of stress. As a result, plants subjected to rapid stress had a young leaf age structure, while plants subjected to gradual stress had an older age structure. Differences among species in tolerance to water stress were related in part to differences in leaf age structure. Species with a young leaf age structure exhibited less of an increase in leaf mortality in response to rapid stress, and more of an increase in leaf longevity in response to gradual stress than other species.Key words: drought tolerance, leaf turnover, leaf age structure, polyethylene glycol, leaf senescence.

ISSN:0008-4026    

DOI:10.1139/b91-209

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Aeciospores ofArthuriomyces peckianusgerminated readily on moist strips of dialysis membrane and developing appressoria were observed within 3 to 6 h after spores were deposited on membranes. A single germ tube typically emerged from each binucleate spore and grew until its tip contacted the dialysis membrane. The germ tube tip was then transformed into a swollen appressorium that adhered tightly to the membrane, apparently as a result of an extracellular material that surrounded the appressorium base. Virtually all the spore cytoplasm and both nuclei moved into the germ tube and developing appressorium. Following a synchronous mitotic division of the two nuclei, a septum formed to delimit the now tetranucleate appressorium from the germ tube. As the appressorium matured, an apparently wall-less region developed in the central portion of the appressorium appressed against the dialysis membrane. In this region the fungus plasma membrane appeared to make direct contact with the underlying dialysis membrane. A funnel-like or cone-like structure referred to as the appressorial cone then developed in the wall-less region. The appressorial cone extended up into the cytoplasm of the appressorium and was lined by the fungal plasma membrane. Numerous branched elaborations of the plasma membrane were associated with the inner portion of the cone.Key words: rust fungus, infection structures, electron microscopy.

ISSN:0008-4026    

DOI:10.1139/b91-210

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

It is commonly asserted in paleoecological studies that shrub birch tends to have smaller pollen than tree birch, but this is poorly documented for Alaskan taxa. We measured freshly dehisced pollen from 55 plants in four northern Alaskan taxa,Betula resinifera(tree birch),Betula glandulosa(shrub birch),Betula nanassp.exilis(dwarf birch), andBetula resinifera×glandulosa(hybrid). No significant differences existed between mean pollen sizes of any taxa.Betula glandulosashowed significant size variation among sites. Increase in birch-pollen size with time observed in some late Quaternary fossil records from northern Alaska cannot be safely attributed to a change from shrub to tree-dominated vegetation. Alternative explanations for temporal trends in pollen size are (i) evolution of populations, (ii) an environmental effect on pollen size, and (iii) local extinction of a previously widespread taxon.Key words: Alaska, Beringia,Betula, late Quaternary, pollen size.

ISSN:0008-4026    

DOI:10.1139/b91-211

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Linear furanocoumarins were found on the surface ofPsoralea bituminosa(Leguminosae) fruits in concentrations up to 1% of the total furanocoumarins. Most of the remainder was on the surface of the embryos and very young seedlings, with ca. 4% of the total furanocoumarins within the embryos, and very little in the seed coat and fruit. Psoralen was present in the highest concentration, over twice that of xanthotoxin. There was very little bergapten, whose distribution differed from that of the xanthotoxin and psoralen, ca. 20% being on the surface and the rest in dead tissues, i.e., fruit and seed covers. Evidence was obtained, through autofluorescence, that these coumarins are localized in discrete cells of the embryo, on the embryo surface, and on the fruit surface.Key words:Psoralea, Leguminosae, fruits, furanocoumarins, autofluorescence, histochemistry.

ISSN:0008-4026    

DOI:10.1139/b91-212

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Cell surface interactions between sorghum roots and the parasitic weedStriga hermonthicawere investigated using light and electron microscopy. An exoglucanase–gold complex was used to study the distribution of cellulose in host tissues of resistant and susceptible cultivars. In the susceptible cultivar, intrusive cells ofS.hermonthicacould reach xylem elements, whereas in the resistant cultivar, development occurred mainly in the outer cortex. Invasion of the susceptible cultivar was accompanied by wall alterations and by the release of cellulose-rich fragments likely detached from host walls through the action of lytic enzymes. The occurrence of wall alterations at a short distance from the point of parasite penetration provided indirect evidence for extracellular diffusion of cellulolytic enzymes. Tylose formation and accumulation of coating material along secondary thickenings of some xylem vessels were late responses observed in the susceptible cultivar. In the resistant cultivar, heavy deposition of successive layers of cellulosic material occurred in outer tissues. Accumulation of this material may constitute a defense reaction against penetration. Electron-dense coating material was noticeable in cortical cells and occasionally in xylem vessels. Defense reactions observed in both sorghum cultivars upon parasite attack differed in their temporal and spatial distribution.Key words:Striga, sorghum, haustorium, root anatomy, gold cytochemistry, cellulose, resistance.

ISSN:0008-4026    

DOI:10.1139/b91-213

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The influence of Al and Ca on the growth, in axenic culture, of three ectomycorrhizal fungi associated with jack pine (Pinus banksianaLamb.) was examined. Isolates ofHebeloma crustuliniforme(St. Amans) Quél.,Rhizopogon rubescens(Tul.) Tulasne, andSuillus tomentosus(Kauff.) Singer, Snell & Dick were obtained from basidiocarps collected in jack pine stands of different ages. Basidiocarps and the soil surrounding them were analyzed for Al and Ca, as well as other elements. Each fungal species was grown for 4 weeks in nutrient solutions containing 37, 185, 370, or 740 μM Al combined in a factorial design with 25, 125, 250, or 500 μM Ca and maintained at pH 3.8. Growth of all three fungal species was reduced at 370 μM Al. Significant interaction was found between fungal species and Al treatment for all six elements measured in mycelial tissue. Stepwise increments in external Al concentration resulted in reduced mycelial concentrations of Ca, Mg, and K, and increased mycelial concentrations of Al, P, and Fe inH.crustuliniforme. High external Al levels resulted in reduced mycelial concentrations of all elements measured except Al and P inR.rubescens. In contrast, forS.tomentosusthe same external Al levels increased the mycelial concentrations of all elements except Ca. The response of the three ectomycorrhizal fungi to Ca also differed. Growth ofH.crustuliniformewas stimulated by stepwise increments in external Ca concentrations from 25 to 500 μM. Increments in calcium had no effect on the growth ofR.rubescens. High external levels of Ca acted synergistically with high external Al concentrations to reduce growth byS.tomentosus. Unlike the other two species, the response ofS.tomentosusto Al and Ca could not have been predicted from the soil and basidiocarp analyses. Alterations in Ca to Al ratios of soils may influence the succession of ectomycorrhizal fungi on conifer root systems.Key words: ectomycorrhizae, jack pine, aluminum, calcium, basidiocarps.

ISSN:0008-4026    

DOI:10.1139/b91-214

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The leaves of the carnivorous bromeliad,Brocchinia reducta, are clustered in a tight vertical rosette, forming a water-collecting tank in which insects are trapped. Evidence in the literature indicates that nutrient uptake into the leaves occurs primarily, if not entirely, via trichomes located at the base of the leaves on the tank side. The outer cell wall in the trichomes from the carnivorous bromeliadB.reductahas an unusual ultrastructure. This wall has a labyrinthine-like appearance of light and dark-staining regions that suggests a highly specialized function. This study examined three structural aspects of this wall. First, the limiting porosity of the trichome wall was examined with fluorescently labelled dextrans and shown to permit the transport of molecules as large as 6.6 nm. Second, structural changes in a dehydrated wall were observed using freeze-substitution techniques. Specifically, the electron transparent wall "regions" were collapsed when the trichome was dried. Last, the presence of periodic acid soluble polysaccharides was detected throughout the electron-dense wall protuberances, but occurred only as thin, dispersed strands in the more electron-transparent regions. We have concluded from these studies that in the hydrated state, these electron-transparent regions represent the channels through which solutes move through the wall to the cap cell surface. A pore size of 6.6 nm would also permit the movement of modest-size proteins, and based on previous observations, we suggest that protein uptake into the cells would occur by pinocytosis. We found channels can vary in size and thus porosity; in the dehydrated state, the wall is considerably shrunken and the channels collapse. We hypothesize that the shrunken wall restricts the loss of water from leaves through trichomes to the atmosphere.Key words: Bromeliaceae, cell wall porosity, fluorescently labelled dextrans, freeze-substitution, Thiéry staining.

ISSN:0008-4026    

DOI:10.1139/b91-215

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Aspergillus flavuswas isolated from soil from a single Arizona cotton field in 1987, 1988, and 1989. Isolates from infected cotton bolls were collected from the same field in 1988. Isolates were assigned to vegetative compatibility groups via complementation tests between nitrate-nonutilizing mutants. Sixty-one of 105 isolates composed 13 vegetative compatibility groups; the remaining 44 isolates could not be assigned to groups. Forty-three isolates from other fields in Arizona composed 21 groups, 6 of which were also found in the test field. Distribution of vegetative compatibility groups in and outside the field was significantly different, based on aG-test. One vegetative compatibility group included 20% of all isolates from the test field, but was not found elsewhere. It was common in the test field in 1987 and 1988, but was not found in 1989. Boll and soil populations from 1988 were not significantly different. Single infected boll locules and 25-g soil samples often containedA.flavusindividuals from more than one group. These results suggest that although many vegetative compatibility groups are widely distributed, a single field may have a unique population profile that changes significantly from year to year.Key words:Aspergillus flavus, vegetative compatibility, Nit−, imperfect fungi.

ISSN:0008-4026    

DOI:10.1139/b91-216

出版商:NRC Research Press    

年代:1991

数据来源: NRC