摘要:

The alpine tundra ecotype ofStellaria longipesis characterized by a dwarf phenotype, whereas the prairie ecotype can be semidwarf or highly elongated depending on its environment. Related to their ability to elongate, these ecotypes also show divergent abilities to produce and respond to ethylene. The prairie ecotype produces a strong daily rhythm of ethylene, which is maintained even following stress events such as wind. The alpine ecotype exhibits a much less pronounced rhythm but greatly increases ethylene production in response to stress. We investigated what differences in ethylene synthesis might be responsible for the ability of the prairie ecotype to produce a large and regular daily rhythm of ethylene production, which in the alpine ecotype is weaker or sometimes absent. Levels of the immediate precursor to ethylene, 1-aminocyclopropane-1-carboxylate (ACC), and its major conjugate, malonyl ACC (MACC) showed no rhythm across the course of a day. Moreover ACC levels remained stable during an entire growth cycle (21 days) in the prairie ecotype, even though ethylene is known to increase especially during periods of rapid elongation. By contrast, assays of ACC oxidase performed in vivo and in vitro showed rhythms of activity similar to those of ethylene production observed in the prairie ecotype. However, the levels of ethylene produced in the ACC oxidase assays were considerably higher than levels of ethylene normally produced by unstressed plants, and the rhythm of ACC oxidase activity was observed in both ecotypes, despite the fact that alpineStellaria longipesexhibits a less pronounced ethylene rhythm. Thus, we concluded that although ACC oxidase activity may partially account for rhythmic production of ethylene in prairie ecotypes, other controlling factors such as spatial separation of ACC from ACC oxidase should be investigated.Key words: ACC oxidase, ecotypes, ethylene, phenotypic plasticity, rhythmicity,Stellaria longipes.

ISSN:0008-4026    

DOI:10.1139/b97-114

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Lythrum salicaria(purple loosestrife) is an exotic weed that arrived in North America from Europe during the early 1800s. It is a herbaceous perennial with a trimorphic breeding system. Seventy-four populations ofL.salicariawere surveyed from Windsor, Ontario, to the Gaspé Peninsula in Quebec. Fifty of the populations were significantly anisoplethic (i.e., unequal frequencies of the three flower morphs), including 10 populations that were nontrimorphic. Populations with fewer than 100 plants tended to have one or even two morphs missing. Although larger populations rarely lacked a morph, they did show significantly skewed morph frequencies. Indices of clonal size, such as number of ramets per genet and genet diameter, differed significantly among sites, and clonal growth also showed significant interaction between morph and site. One-way analyses of variance indicated that morphs differed in terms of either number of ramets per genet or genet diameter in 16% of populations. Morphometric analyses of flowers from 49 populations showed significant variability in floral traits among genets, flower morphs, and sites. Results indicated frequent reduction in herkogamy (spatial separation between anther and stigma), with variant flowers having very little or no stigma–anther separation. Mean stigma–anther separation was lowest in the mid-morph individuals, followed by the short and long morphs. Correspondingly, the frequency of variant flowers was greatest in mid-morph individuals and least in long-morph individuals. Isoplethic and anisoplethic populations did not differ, for any morph, in the frequency of occurrence of these variant flowers.Key words:Lythrum salicaria, purple loosestrife, isoplethy, morph frequency, heterostyly, variant flowers, stigma–anther separation.

ISSN:0008-4026    

DOI:10.1139/b97-115

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Freshwater hyphomycete communities of autumn, based on data generated by three techniques used simultaneously, were richer than those detected by these techniques used singly. The fungal communities in the acidic streams were poorer (28–32 species) than in the circumneutral streams (39–64 species). No significant correlation was found between number of fungal species and pH of the stream water. Combining the data from this study with those of studies by other authors using the same techniques, linear correlation and regression analyses revealed the significant negative correlation between species composition of communities in a stream and its pH. The number of fungal species in assemblages detected by different techniques used singly (e.g., filtration of stream water or examination of foam concentrate) or communities based on data generated by these techniques used simultaneously versus pH values formed a unimodal curve with a maximum at a pH between 6 and 7, mostly at 6.7. The conidial dynamics were influenced by the riparian vegetation. Conidium production from submerged deciduous and conifer litter was determined under laboratory conditions. Generally conidium production per disc was higher forAnguillospora longissima(Sacc. & Syd) Ingold,Flagellospora cumulaIngold,Lunulospora curvulaIngold, andTetracladium marchalianumde Wildeman in deciduous leaves than conifer leaves.Heliscus lugdunensisSacc. & Therry,Alatospora acuminataIngold, andArticulospora tetracladiaIngold produced more conidia per disc in conifer than in deciduous leaves. Percentage similarity between spora produced by submerged substrate and stream spora was higher for deciduous substratum than for coniferous substratum in five circumneutral streams with a riparian vegetation dominated by deciduous trees. This index was higher for coniferous substratum in three acidic streams in which coniferous and deciduous trees were evenly distributed. The fungal communities in the Nosehri, Pathika, and Jabbar Camp streams showed higher values of species diversity than in other streams.Key words: freshwater, hyphomycetes, species diversity.

ISSN:0008-4026    

DOI:10.1139/b97-116

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The Clavicipitaceae (Ascomycotina) are unique among biotrophs in that they do not produce haustoria to extract nutrients from hosts. Stromata are usually formed on developing parts of the host and are composed of a mixture of host and fungal tissues. An ultrastructural examination of stromata ofEpichloë amarillanswas conducted to assess changes in host tissues associated with development of stromata on grasses. Notable changes were observed in the epidermal layers of leaves and inflorescence primordia embedded within stromata. Epidermal cells within stromata showed progressive disintegration of the cuticle and wall layers. These alterations effectively broke down the epidermal barrier to the flow of nutrients and water to fungal tissues that develop outside the plant tissues. Mycelium was observed to associate closely with host cells. No penetrations of cells of the mesophyll, phloem, or xylem were observed; however, some alteration of the host cell walls was detected. Host cell walls proximal to hyphae were often seen to be slightly thicker than walls adjacent to other plant cells. Unseen alterations to host cell membranes are hypothesized. A mechanism of nutrient flow from host to stromal mycelium is discussed. The modification of host cells and tissues to enhance nutrient flow to fungal reproductive structures, without the development of haustoria, is suggested to be a basic mechanism of nutrient acquisition among biotrophic fungi.Key words: Clavicipitaceae, endophyte,Epichloë, nutrient acquisition, ultrastructure.

ISSN:0008-4026    

DOI:10.1139/b97-117

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The function of glutamate dehydrogenase was studied in cultured sweetpotato (Ipomoea batatas) nodal explants. The glutamate dehydrogenase was fractionated to charge isomers. Supplementation of the growth medium with either naphthaleneacetic acid or benzyladenine in the presence of 20 mM NH4NO3induced normal growth (type 1 sweetpotato). The basic and acidic charge isomers of glutamate dehydrogenase were not suppressed. Combined supplementation with 70 mM NH4+and either 1 mg ∙ L−1benzyladenine or 0.1 mg ∙ L−1naphthaleneacetic acid caused growth retardation (type 2 sweetpotato) and the suppression of the basic charge isomers. Combined supplementation with 45 mM NH4+and either 1 mg ∙ L−1benzyladenine or 0.1 mg ∙ L−1naphthaleneacetic acid induced normal growth (type 3 sweetpotato), but the acidic charge isomers were suppressed. Combined supplementation with benzyladenine and naphthaleneacetic acid suppressed all the charge isomers and abolished amination by the enzyme, thereby causing severe growth retardation. The type 1 and type 3 sweetpotato glutamate dehydrogenases were more aminating (Michaelis constantKm = 12.5 and 14.8 mM NH4Cl, respectively) than type 2 sweetpotato glutamate dehydrogenase (Km = 82.6 mM NH4Cl). The differential growth retardations which accompanied the three phases of the suppression of the aminating charge isomers are evidence that the enzyme is aminating in vivo and that it employed that activity in the regulation of sweetpotato growth and differentiation.Key words: glutamate dehydrogenase, amination depression, sweetpotato reta

ISSN:0008-4026    

DOI:10.1139/b97-118

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The leaves of the majority ofBegoniaspecies are asymmetrical. To shed some light on the nature of this asymmetry, the authors followed the development of the first forming leaves in two species with very different adult shapes:Begonia subvillosa, which has strongly asymmetrical leaves and palmate venation, andB.fagifolia, which has pinnate venation and symmetrical leaves. Key stages of the development were identified. First, there is no asymmetry within the embryo. In both species, the leaves of the first two nodes are asymmetrical in the early stages. However, they lose this asymmetry during development and show a palmate venation. From the third node on, the two species show some differences. The leaf ofB.subvillosakeeps its initial asymmetry and part of its blade develops into an auricle, unlike the leaf ofB.fagifolia. From the fourth node on, the leaf ofB.fagifoliais pinnately veined. The central area of the leaf blade of both species settles to its adult shape much earlier in development than other areas of the leaf. The different parts of the blade acquire their adult characteristics successively according to different timing sequences.Key words: Begoniaceae, development, leaf, morphogenesis, symmetry.

ISSN:0008-4026    

DOI:10.1139/b97-119

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

An inspection of 12-year-old, copper–chrome–arsenate (CCA) treatedPinus radiatawood from an industrial cooling tower showed extensive surface decay of wood. Electron microscopic examination of decaying mild compression wood indicated that compression wood cells were attacked exclusively by bacteria, which were of erosion and tunnelling types. The highly lignified outer S2 wall and the middle lamellae in the compression wood tracheids were resistant to erosion bacteria, and were only occasionally attacked by tunnelling bacteria. These observations are discussed in relation to the information available on the structure and chemical composition of compression wood.Key words: compression wood, bacterial attacks, CCA-treated wood,Pinus radiatawood, erosion bacteria, tunnelling bacteria.

ISSN:0008-4026    

DOI:10.1139/b97-120

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Wounded and nonwounded micropropagated shoots ofCupressus sempervirensandChamaecyparis lawsonianawere inoculated in vitro with the canker-causing pathogensSeiridium cardinale(Wag.) Sutton & Gibson,Seiridium cupressi(Guba) Boeswinkel andSeiridium unicorne(Cke & Ell.) Sutton.Seiridium cardinalewas significantly more pathogenic onCupressus sempervirensthan onChamaecyparis lawsoniana(Murr.) Parlatore, irrespective of the presence of wounds on the shoots. On wounded shoots, bothS.cupressiandS.unicornecaused significantly larger lesions onChamaecyparis lawsonianathan onCupressus sempervirensby 20 days after inoculation. Superficial wounding of shoots prior to inoculation caused a significant increase in the lengths of lesions and numbers of shoots girdled by the pathogens on both hosts. These results broadly correlate with known virulence of the three pathogens on these two host tree species in field and glasshouse tests. Using histological methods, penetration of fungal hyphae through stomatal pores of both shoots and leaves into the substomatal cavity and the mesophyll space was observed. Penetration directly through the cuticle was also seen. Defence-related responses, including accumulation of oxidized polyphenols compounds and deposition of lignin and suberin in cell walls, were detected in inoculated tissues. These responses occurred predominantly in the epidermis, including stomatal guard cells, and the hypodermis and were particularly marked inChamaecyparis lawsonianainoculated withS.cardinale. The possible utility of these methods in the study and detection of host genotypes resistant toSeiridiumspp. is discussed.Key words:Seiridium,Cupressus,Chamaecyparis, micropropagation, in vitro inoculation, defence.

ISSN:0008-4026    

DOI:10.1139/b97-121

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Ombrotrophic peatlands in North America are harvested mainly for horticultural purposes. Following intense exploitation, these peatlands are generally abandoned to natural regeneration. The abandoned sites usually remain barren or poorly revegetated by a few vascular plants for several years. The post-harvested sites are not usually recolonized bySphagnumspecies (peat mosses), which are the key species to restore peatland functions. The objective of this study was to develop restoration techniques for post-harvested peatlands. The experiments centred onSphagnumreintroduction, since peat mosses are responsible for peat accumulation. VegetativeSphagnumfragments were used as diaspores. Various methods ofSphagnumreintroduction were tested to ensure reliable colonization. A microrelief formed of ridges and depressions provided humid conditions in depressions which favoredSphagnumestablishment. ReintroducingSphagnumdiaspores in combination with such companion plant species asEriophorum angustifoliumalso had a positive effect on the survival of peat mosses. A phosphorus amendment led to improved establishment of Sphagna and companion plant species.Key words:Sphagnum, microtopography, companion species, phosphorus, fertilization.

ISSN:0008-4026    

DOI:10.1139/b97-122

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This paper provides details on the infection processes at the ultrastructural level inPinus resinosaAit. seedlings during early stages of colonization byGremmeniella abietina(Lagerb.) Morelot. Different gold-conjugated enzymes and antibodies were used to cytochemically localize cellulose, pectin, fungal laccase, and the pathogen cells in host tissues.Gremmeniella abietinapenetrated into the host through stomata of the short shoot bracts and sparsely colonized both intercellular and intracellular areas of the bract tissues. The colonizing hyphae usually had a thick wall surrounded by an extracellular sheath composed of fibrillar material. Microhyphaelike cells were observed as having penetrated host cell walls. The fungal cells (except the extracellular sheath), even when embedded in cellulosic or pectic material of host tissues, did not appear to contain cellulose or pectin. We suggest thatG.abietinais able to degrade cellulose and pectin and that phenoloxidases secreted by the pathogen could be involved in host cell wall degradation. The results indicate that the extracellular sheath ofG.abietinais implicated in host–pathogen interactions such as attachment of hyphae to the host surface and cell wall degradation during colonization of host tissues.Key words:Gremmeniella,Pinus, infection processes, cell wall degradation, extracellular fungal sheath, gold labelling.

ISSN:0008-4026    

DOI:10.1139/b97-123

出版商:NRC Research Press    

年代:1997

数据来源: NRC