摘要:

Within a multidisciplinary study of terrestrial ecosystems of the Haut-Saint-Laurent Regional County Municipality, the vegetation of "Large Teafield" and "Small Teafield" peatlands is described from 127 stands. Detrended correspondence analysis and correlations between data indicate that the greatest vegetational variation is expressed by variables related to trophic regime (e.g., pH of peat) and moisture regime (e.g., organic content). In addition to gradient analysis, hierarchical clustering combined with reference to contingency tables is used to characterize the typology along gradients. Mapping of the community types partially relates the distribution analysis to a circular spatial pattern of the vegetation. Highly oligotrophic sites are colonized by low shrubs.Chamaedaphne calyculatais found at the centre of the peatlands, where the peat deposit is thick and fire does not play an important role. Low shrubs dominated byBetula populifoliasurround theChamaedaphne calyculatavegetation and are more affected by burning towards the perimeter. Heavily burned sites are dominated byEpilobium angustifolium. The perimeters of the peatlands are colonized byBetula populifoliaorPopulus tremuloidesopen forests, while the most stable forests are dominated byAcer rubrum. Some marshes and swamps are present where the peat deposit is thin. Sixteen community types are described for the study area.

ISSN:0008-4026    

DOI:10.1139/b87-271

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

In tomato (Lycopersicon esculentumMill. cv. St-Pierre), an adaptation to 75 or 100 mMNaCl, which results in an increase in growth, is obtained after transferring on media gradually enriched in NaCl, during four generations, either terminal parts of stems (including terminal bud and last internode) or calli initiated from roots or stems. Conversely, no growth increase is obtained at the fourth generation, when the culture medium has a NaCl concentration similar to that of the preadaptation medium of calli or young plants of the three previous generations. A comparison between the growth of calli and that of young plants originating from transfer of terminal parts of the stem reveals that the latter have the best NaCl adaptative abilities. Among the factors linked to the adaptative process at the level of cell masses of calli or at the level of differentiated cells of young plants are Na and Cl content, a decrease of Cl/Na ratio, an increase of K, Ca, or soluble sugar contents, the proline synthesis, a repartition of ions or metabolites proportional to accumulated masses, and an increase of peroxidase activity in plant roots.

ISSN:0008-4026    

DOI:10.1139/b87-272

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Low-temperature scanning electron microscopy of frozen-hydrated specimens and transmission electron microscopy of cytochemically stained thin sections and enzymically digested samples have been used to study the pattern of colony development from the initial infection in the substomatal chamber of the leaf to the production of urediniospores within uredinia. Rapid immobilization of leaf samples by freezing enables them to be fractured, revealing information on internal structural relationships between intercellular hyphae and host cells. Extracellular matrix substances, which are well preserved by low-temperature scanning electron microscopy, play an important role in the cohesion of hyphae during the early stages of uredinium formation. Cytochemical staining indicates the presence of two such matrix materials: (i) colloidal iron-negative matrix surrounding intercellular hyphae, forming a pad between adjacent hyphal cells and (ii) a colloidal iron-positive matrix between hyphal and host cell walls. A positive reaction with colloidal iron indicates acidic mucopolysaccharides. Enzymic digestion with pronase and the staining reaction with silicotungstic acid – chromic acid suggests that a glycoprotein is present in the matrix surrounding intercellular hyphae. Possible roles for the extracellular matrix, including hyphal cohesion, cell–cell communication, and protection against desiccation, are discussed.

ISSN:0008-4026    

DOI:10.1139/b87-273

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The development of the spines and the structure and composition of the urediniospore wall ofUromyces viciae-fabaehave been studied by low-temperature scanning electron microscopy, cytochemical localization, chemical, and enzymic digestion techniques. Spine formation was similar to that previously described for urediniospores of other rust fungi. Swollen collars that are distinct from the annular ridges are only evident in frozen-hydrated spores and surround the bases of spines. Pockets of endoplasmic reticulum line the periphery of spores and mark the sites of spine development. This endoplasmic reticulum may have a role in the production of enzymes and (or) structural proteins or glycoproteins. Microfibrils are present in digested and shadowed wall preparations, often associated with spines. Enzymic digestion treatment suggests that these microfibrils are chitin. Around the bases of the spines, microfibrils are orientated circumferentially and contribute in part to the thickened, annular ridges evident in all spore preparations. The spore wall matrix consists of polysaccharides. Colloidal iron staining indicates acid mucopolysaccharides. Differences in reaction of the urediniospore wall to colloidal iron at what appears to be the same stage of development suggestsin situchemical change(s), which may in turn be linked with changes in wall plasticity.

ISSN:0008-4026    

DOI:10.1139/b87-274

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Photocontrol of hypocotyl elongation in etiolatedSinapis albaL. seedlings was investigated using a high-resolution growth-measurement system. Different photoresponses were characterized by the dynamics of plant response to monochromatic irradiations at wavelengths ranging from 380 to 780 nm. Brief puises of 660- or 670-nm red light caused a large, rapid inhibition of growth rate after a lag of ca. 5 min. Growth rate remained depressed for several hours following a single red light pulse. If given 120 min or less after the red light, a 740-nm far-red pulse reversed the inhibitory effects of prior red light treatment after a lag of ca. 6 min. Most seedlings did not respond to single far-red irradiations in the 720- to 780-nm wave band, although some underwent small depressions in growth 5 to 10 min after the end or irradiation. Irradiation with 450-nm blue light caused a deeper inhibition than red light after a lag of only 1 min. Recovery from inhibition by blue light was rapid, unless the irradiation was prolonged. Removal of the plumule and cotyledons did not affect the dynamics of the rapid blue and red – far-red growth responses. The rapid response to red light occurred at wavelengths from 550 to 710 nm. The rapid blue response occurred only from 380 to 500 nm. Within each of these wave bands, the depth of photoinhibition was nearly constant. However, the duration of photoinhibition by red light declined from about 3 h after a 660-nm pulse to about 45 min after a 710-nm pulse. Elongation in etiolatedSinapishypocotyls is thus controlled by a classical phytochrome-mediated induction-response system and by the blue light photoreceptor. Photoinhibition of hypocotyl elongation by red light required a minimum of about 5% of total phytochrome to be in the far-red absorbing form.

ISSN:0008-4026    

DOI:10.1139/b87-275

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Eleven species ofHordeumwere tested for their reaction toUstilago nuda(Jens.) Rostr. andU.tritici(Pers.) Rostr., the causes of the embryo-infecting loose smuts of cultivated barley and wheat, respectively. The speciesHordeum chilenseandH.depressumwere resistant, whileH.euclaston,H.halophilum,H.procerum,H.pusillum, andH.stenostachyswere susceptible to both fungi.Hordeum muticumwas susceptible only toU.nuda, whileH.arizonicum,H.lechleri, andH.roshevitziiwere susceptible only toU.tritici. The susceptible species are new hosts for these pathogens. It is proposed that these results, together with those of an earlier study, indicate thatU.nudaevolved fromU.tritici.

ISSN:0008-4026    

DOI:10.1139/b87-276

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Seed banks were examined in four plant communities in a high-elevation sphagnum bog in West Virginia, U.S.A. A germination assay was used to detect germinable seed densities. Vertical depth distributions were determined for one community in which the soil cores were transported intact to the greenhouse. Seed densities ranged from 12 874 in aSphagnum-dominated community to 377 041 seeds m−2in a sedge-dominated community. The seed bank in all communities was dominated numerically byJuncus effusus, although this species comprised a minor part of the aboveground vegetation. Three types of depth profiles were observed, including one distribution showing a simple decline in seed numbers with depth, another showing a unimodal peak below the soil surface, and a third with two distinct peaks at depth. A matrix model of seed burial was devised to account for the different depth profiles. By assuming that soil compression occurred and that the rate of compression declined with time, the model showed that either of the first two depth profiles could be produced with no need to invoke a historical change in the seed rain. The model was unable to account for the bimodal depth profile with the assumption of a constant seed rain. However, the fact that the model of seed burial could explain a unimodal peak in the depth profile suggests that simple historical interpretations of past abundance using a buried seed profile are difficult.

ISSN:0008-4026    

DOI:10.1139/b87-277

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Detailed observations and experimental studies of the reproductive biology of 12 boreal forest herbs were conducted over a 3-year period (1978–1980) in spruce–fir forests of central New Brunswick. The species examined wereAralia nudicaulis,Chimaphila umbellata,Clintonia borealis,Cornus canadensis,Cypripedium acaule,Linnaea borealis,Maianthemum canadense,Medeola virginiana,Oxalis montana,Pyrola secunda,Trientalis borealis, andTrillium undulatum. All taxa are insectpollinated perennials and most exhibit clonal growth. Floral syndromes of the understory community are relatively unspecialized with many species possessing small white or green flowers. A total of 103 taxa of insects were collected from flowers during the 1979 season.Bombusspp. are the major pollinators of 5 of the 12 species. Syrphid flies, bee flies, and halictid and andrenid bees were also commonly observed. Controlled pollinations were undertaken to determine the breeding systems of herbs. Bagged, self-, cross- and open-pollinated treatments were used to investigate the capacity for self-pollination, compatibility status, and factors influencing fecundity in each species. A diversity of reproductive systems was revealed. Six species are completely dependent on insects for pollination, four species are weakly autogamous, one is strongly autogamous, and one appears to be apomictic. Comparisons of fruit-set and seed set from controlled self- and cross-pollinations indicate that four species are strongly self-compatible, one is dioecious, and the remainder display varying degrees of self-incompatibility. Despite this variation, outbreeding appears to be the most common reproductive mode. In several species there is evidence that low pollinator service limits fruit-set.

ISSN:0008-4026    

DOI:10.1139/b87-278

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The flowering and fruiting phenologies of 12 boreal forest herbs were recorded during 1979 (flowering and fruiting) and 1980 (flowering only) in spruce–fir forests of central New Brunswick. The species studied wereAralia nudicaulis,Chimaphila umbellata,Clintonia borealis,Cornus canadensis,Cypripedium acaule,Linnaea borealis,Maianthemum canadense,Medeola virginiana,Oxalis montana,Pyrola secunda,Trientalis borealis, andTrillium undulatum. Flowering in the community occurred from mid-May to the end of July. The order of flowering was maintained in the 2 years, but the degree of synchronization of inflorescences differed in several species. Fruiting in the community began in mid-July and extended beyond the end of September. The percentage of buds that ultimately bore fruit ranged from 0 (Cypripedium acaule) to 61% (Aralia nudicaulis). With the exception ofCypripedium acaule, which received little pollinator service, the self-incompatible species,Cornus canadensis,Maianthemum canadense, andMedeola virginiana, experienced the lowest levels of fruit-set. Pollen limitation and predation of developing fruit appear to be the major factors limiting percentage fruit-set in boreal forest herbs. Fruit production varied with time of flowering of inflorescences in several species, with periods of low fruit-set tending to coincide with lower densities of flowering inflorescences. Significant rates of fruit removal by herbivores occurred in all sarocochorous species. Disappearance of fruits from infructescences ranged from 31 (Medeola virginiana) to 95% (Aralia nudicaulis), with highest removal rates occurring during periods of greatest fruit availability.

ISSN:0008-4026    

DOI:10.1139/b87-279

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The downy mildew fungus (Plasmopara halstedii) sporulated on callus tissue of sunflower (Helianthus annuus) in dual cultures on tissue culture medium. The fungus was most concentrated in the seven outermost layers of the callus. No haustoria were found inside the host cells. Healthy callus from both susceptible and resistant sunflowers was successfully inoculated with pieces of the dual cultures, giving rise to mycelium but no spores on the fresh callus. Dual cultures developed at comparable rates in both the compatible and incompatible combinations; the downy mildew resistance of intact plants was not expressed in dual cultures under the environmental conditions used.

ISSN:0008-4026    

DOI:10.1139/b87-280

出版商:NRC Research Press    

年代:1987

数据来源: NRC