摘要:

Seeds of the orchidsPlatanthera hyperborea,Spiranthes lacera, andSpiranthes sinensiswere germinated in vitro in the presence of compatible fungal species and the resulting colonized protocorms were studied by light microscopy, transmission electron microscopy, and colloidal-gold affinity techniques. Protocorm cells in early stages of colonization contained coils of fungal hyphae (pelotons) separated from host cell cytoplasm by the host plasma membrane and interfacial matrix material. Host cell walls were labelled by the colloidal gold – cellobiohydralase I (CBH-I) complex to detect cellulose and, particularly over the middle lamella, by antibodies that bind to pectins (JIM 5 and JIM 7). A polyclonal antibody that binds to β-1,3-glucans labelled the fungal cell wall heavily. None of the probes, however, labelled the interfacial matrix between the wall of active fungal hyphae and the surrounding plasma membrane. In contrast, the interfacial matrix material that ensheathed collapsing hyphae showed labelling after treatment with JIM 5, the polyclonal antibody, and the CBH-I complex. Labelling of host cell walls and fungal walls was similar to that described for early stages.Keywords: orchids, protocorms, mycorrhizas, affinity gold techniques, interfacial matrix.

ISSN:0008-4026    

DOI:10.1139/b96-223

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The double-flowered variety ofHibiscus rosa-sinensisL. (Malvaceae) displays a divergent floral morphology that appears to fit the criteria for homeosis. A comprehensive definition defines homeosis as the complete or partial replacement of one part of an organism with another part. The corolla of the single flower is pentamerous. The mature flower has a staminal tube bearing 60 – 70 stamens that surrounds an exserted synstylous gynoecium with five fused stigmas. In double flowers, the outermost whorl of petals is similar in appearance to that of the single flower. The remaining floral appendages have a morphology that is intermediate between petals and stamens, to varying degrees. No two double flowers are exactly the same, even on the same plant. As with other members of the Malvaceae, floral development in both floral types is unusual: once the calyx has been initiated, a ring meristem is formed from which both petal and stamen primordia are initiated. In the single flower, petal primordia are initiated on the flank of the ring, and then stamen primordia arise in five distinct and orderly clusters. In the double flower, petal primordia are also initated on the abaxial flank, but the remainder of the ring initiates primordia that form a mixture of petals, petal – stamen intermediates, and stamens. A common ring meristem that has two different developmental pathways provides a novel opportunity to study homeosis from the perspective of comparative developmental morphology.Keywords: homeosis,Hibiscus rosa-sinensis, androecium, intermediates, ring meristem, floral development.

ISSN:0008-4026    

DOI:10.1139/b96-224

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Three cycles of successive trap cultures were utilized to determine the taxonomic structure of arbuscular fungi associated with mesquite (Prosopisspp.) from three locations in the Sonoran desertscrub biotic community and one location in the Chihuahuan desertscrub biotic community. Unlike the low species richness found in previous studies of some arid habitats, seven to nine species were recovered from each sampling site. This number is comparable to that found in many other plant communities. Seventy-five percent of the species found after three culture cycles were not detected in the first trap cultures, suggesting that a high proportion of arbuscular fungi in arid habitats may be nonsporulating in the field. Low colonization levels may account for the absence of sporulation, but ecological factors such as moisture limitations also may be involved. Although a total of 10 different species was detected, generic richness was limited, with 9 of these species inGlomusand 1 inEntrophospora. As long as measurement of species richness is based on occurrence of sporulation, successive trap cultures provide a means of detecting nonsporulating mycorrhizal colonizers in arid and other habitats.Keywords: vesicular – arbuscular mycorrhizae, ecology, desert, Glomales.

ISSN:0008-4026    

DOI:10.1139/b96-225

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Seasonal changes in the freezing tolerance in situ were determined forOpuntia fragilisandOpuntia polyacanthanative to southern Saskatchewan, Canada. Wintering terminal cladodes ofO.fragilisandO.polyacanthasurvived −50 and −40 °C, respectively, without any apparent tissue injury. Approximately 50% of the cladodes ofO.fragiliscollected on either 10 October or 10 December 1985 tolerated −70 °C and immersion in liquid nitrogen (−196 °C) following slow prefreezing to −40 °C. These are the lowest values reported for the freezing tolerance of cacti as determined by regrowth and tissue necrosis. Newly formed cladodes of the same species did not tolerate −3.5 °C in June, but freezing tolerance increased from −7 to −50 °C from 6 September to 10 October. This increase in freezing tolerance was accompanied by a decrease in water content from 5.4 to 2.6 g H2O/g dry wt. and the cladodes were shrunken and reduced by approximately 30% in diameter. AlthoughOpuntiais a succulent plant that avoids drought by storing water in the cladodes, during cold acclimationO.fragilisappears to shift to a more drought-tolerating strategy. In midsummer, the current year cladodes ofO.fragilistolerated a 60-min exposure to 50 °C, while the previous year cladodes tolerated 55 °C without any visible symptoms of injury. Temperature extremes of −30 and 51 °C were recorded at the microhabitats ofO.fragilis. This study demonstrates that this species can acclimate to tolerate both the high and low temperature extremes experienced in its native habitat.Keywords: cacti, cold acclimation, freezing tolerance, heat tolerance,Opuntia, water relations.

ISSN:0008-4026    

DOI:10.1139/b96-226

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Ericoid mycorrhizae are complex organisms consisting of fungal and plant components, and their formation requires enzymatic synergisms and mutualist compatibilities resulting from cooperation of recognition and defense systems of both plant and fungus. Despite this, the plants that form this symbiosis are treated as three separate families in the Ericales: the Ericaceae, the Epacridaceae, and the Empetraceae. In this study, I used the anatomy, physiology, and symbiont compatibility of mycorrhizae (mutualistic interactions between plant roots and fungi) to formulate the hypothesis that the ericoid mycorrhiza-forming plants in the Ericaceae, Epacridaceae, and Empetraceae have a single phylogenetic origin within the Ericaceae coincident with the advent of ericoid mycorrhizae. I tested this hypothesis by parsimony analysis of newly generated and previously published partial 28S ribosomal RNA gene sequences (nuclear) and rbc-L (chloroplast) sequences obtained from GenBank. All results supported the hypothesis that ericoid mycorrhiza-forming plants have a single phylogenetic origin and indicated that the Epacridaceae and Empetraceae should be included within a broadly defined Ericaceae.Keywords: Ericales, 28S ribosomal RNA gene, mycorrhizae, molecular phylogenetics, Empetraceae, Epacridaceae.

ISSN:0008-4026    

DOI:10.1139/b96-227

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

To describe the different types of geotropic reactions of hevea (Hevea brasiliensis), young seedlings were cultivated in root observation boxes and submitted to a double gravistimulation (90° rotation of the minirhizotrons in the vertical plane). It was demonstrated that the taproot is a strongly orthogeotropie organ since it resumed rapidly its prestimulation vertical position. Morphological and morphogenetic modifications were associated with the geotropic response: reduced speed of growth coupled with a reduction of the apical diameter as well as an alteration of ramification density in the curving zone and the following one. Early secondary roots showed a somewhat reduced orthogeotropism that was weaker as the growth direction before gravistimulation was more distant from the vertical. Secondary roots of the acropetal sequence were semiplagiotropic, that is only those roots oriented upward after the gravistimulation resumed, more or less, the original direction. Tertiary roots didn't respond to the gravistimulation and therefore were ageotropic. Complementary observations conducted in large laboratory rhizotrons showed that late forming secondary roots were plagiotropic in their younger stages, thereafter loosing most of their sensitivity to gravity. Quaternary roots were ageotropic. On the basis of these data, a geotropic gradient was defined within the hevea root system, where the strongly responding taproot and late secondary roots are opposed to the weakly or nonresponding tertiary and quaternary roots. Functional significations of these differential geotropic reactions in different hevea root types are discussed.Keywords: geotropism, gravistimulation, root system, growth, development, morphogenesis, root observation box,Hevea brasiliensis. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b96-228

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Variation in the ribosomal (rDNA) repeat was analyzed for 107 isolates of the pathogenic fungusChondrostereum purpureum, collected from Europe, New Zealand, and North America. The rDNA repeat of a representative Canadian isolate ofC.purpureumwas cloned into the λ vector EMBL-3, and a detailed restriction map was constructed. Variation in the large non-transcribed spacer region of the rDNA was determined for the entire collection of isolates following amplification by the polymerase chain reaction (PCR) and analysis of restriction fragment length polymorphisms (RFLPs). Three distinct nuclear type patterns were identified using the restriction endonucleaseHaeIII. Nuclear type I was found in North American, European, and New Zealand isolates. Nuclear type II was only detected in isolates collected from North America, and nuclear type III was observed in isolates collected from both Europe and New Zealand. Nuclear type I was the predominant nuclear type in eastern North America as indicated by a frequency of 0.78, and nuclear type II occurred with a frequency of 0.89 in western North America. Gene flow across the continent was indicated by nearly equal nuclear type distributions (nuclear type I, 0.41; nuclear type II, 0.59) in central North America, but geographic separation has led to unequal nuclear-type distributions across North America.Keywords:Chondrostereum purpureum, biological control, genetic variation, ribosomal DNA.

ISSN:0008-4026    

DOI:10.1139/b96-229

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Disease incidence, disease severity, areas under the disease incidence and disease severity progress curves, and maximum and minimum incidence and severity of disease were evaluated as measures of resistance in canola (Brassica napus) to blackleg caused byLeptosphaeria maculans. Seven genotypes of spring canola were tested in Ontario at three locations 60, 81, and 102 days after sowing in 1990 and at two locations 55, 70, 85, and 100 days after sowing in 1991. Disease incidence was expressed as the percentage of sampled plants with basal stem canker, and disease severity was assessed as the percentage discolouration of a cross section of the stem base. Based on ease of measurement, range of values, number of significant differences among genotypes, and constancy of rank of genotypes at different locations, measures of disease severity or disease incidence in mature plants proved to be most useful. No advantage was gained by using area under the disease incidence and disease severity progress curves, or maximum and minimum incidence and severity of disease at the last sampling time. It is recommended that resistance of canola stems to blackleg be evaluated from measures of disease severity or disease incidence in mature plants.Keywords: canola, blackleg,Leptosphaeria maculans, resistance measurements.

ISSN:0008-4026    

DOI:10.1139/b96-230

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The feather moss community in upland black spruce stands is dominated byPleurozium schreberi, with small pure colonies and mixtures of ubiquitous and apparently persistent minor species. Previous studies indicated that this spatial pattern is not due to microsite conditions. This study tested the hypothesis that the minor species persist by dynamic occupation of small disturbance-type gaps. Colonization of experimental gaps (10 cm diameter, three substrate types) was tracked over 2 years to determine (i) howPleuroziumand the three minor species colonize gaps and (ii) how characteristics of the gaps affect colonization. All species colonized by encroachment of surrounding vegetative shoots. Availability of propagules, i.e., species composition of the surrounding bed, had the greatest impact, but regeneration of two species was affected by substrate:Ptiliumgrowth was reduced on spruce needles, whereas that ofPtilidiumwas increased.Pleurozium schreberidisplayed the most rapid growth in terms of shoot encroachment regardless of gap characteristics. By virtue of its abundant propagules and rapid growth,Pleuroziumis most likely to colonize randomly located disturbance-type gaps, hence maintaining its dominance. Differentiation in regeneration characteristics does not account for the persistence of the minor species in the community.Keywords:Pleurozium schreberi,Ptilium crista-castrensis,Dicranum polysetum,Ptilidium ciliare, gap dynamics, community structure.

ISSN:0008-4026    

DOI:10.1139/b96-231

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Sex expression ofTaxus brevifoliaNutt. was studied at four sites in western Oregon. Of 115 trees examined, 17 were cosexual. All cosexual trees had predominantly male sex expression, suggesting that male sterility is much more constant than female sterility forT.brevifolia. Some implications of the observed patterns are discussed, along with suggestions for further research.Keywords:Taxus brevifolia, yew, sex expression, dioecy.

ISSN:0008-4026    

DOI:10.1139/b96-232

出版商:NRC Research Press    

年代:1996

数据来源: NRC