摘要:

Characteristics of the enzymes involved in the assimilation of NO3−and NH4+, in particular the nitrate and nitrite reductases, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, glutamate decarboxylase, and asparagine synthetase, are described. The cellular organization of these enzymes in root and leaf tissues are assessed in view of recent research developments that utilize various tissue blotting techniques. Regulation of nitrate assimilation is analyzed at the physiological, biochemical, and molecular levels.Key words: nitrate, ammonium, assimilation, regulation.

ISSN:0008-4026    

DOI:10.1139/b94-094

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This brief history of mycology in Canada has comments on the activities of more than 200 men and women. Emphasis is on those aspects of mycology in which Canadian mycologists, plant pathologists, forest pathologists, and geneticists have pioneered or excelled. It includes their studies on fossil fungi, aeromycology, the identity of wood destroying fungi in their mycelial stages, the coevolution of parasitic fungi and their host plants, mycotoxicology, psychrophilic fungi, predacious fungi, fungal genetics, and mycorrhizae, in addition to systematics, numerical taxonomy, and the use of computers in mycology.Key words: fossil fungi, fungal genetics, coevolution, predacious, mycorrhizae, taxonomy.

ISSN:0008-4026    

DOI:10.1139/b94-095

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

We investigated physiological integration among ramets ofSpartina patenswhen clones spanned a salinity gradient. Clones ofS.patenswere grown in paired pots with the ramets of the parent pot connected to the ramets of the daughter pot via a common rhizome. Half of these clones had the rhizome connection between parent and daughter pots severed immediately prior to treatment application. The parent pots were kept at low salinity (34.2 mM NaCl) and given two levels of labeled15NH4Cl (0.036 or 0.714 mM NH4Cl). Daughter ramet pots were kept at the low N level (unlabeled 0.036 mM NH4Cl) and exposed to an increase in salinity to 513 mM NaCl. After 7 days, all daughter ramets had significantly elevated leaf Na levels. Daughter ramets connected to parents were able to maintain significantly greater leaf elongation rates than severed daughter ramets. Labeled15N was translocated from parents to connected daughter ramets and high-N parents translocated more N to the belowground tissue of daughter ramets than low-N parents. Leaf proline, a nitrogen-containing osmoticum that accumulates only after a threshold of salinity stress is exceeded, was significantly increased only in severed daughter ramets, indicating that salinity stress was reduced in connected daughter ramets, possibly via parental water translocation.Key words: clone, physiological integration, proline, ramet, salt marsh, salt stress.

ISSN:0008-4026    

DOI:10.1139/b94-096

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Soil samples from the northern United States in regions subject to acid deposition and from other regions where acid deposition is not a problem were cultured so that estimates of myxomycete frequency could be made. The presence of myxomycetes, protostelids, cellular slime molds, myxobacteria, and nematodes was recorded as were physical and chemical characteristics of the soils. No significant correlations were noted between the numbers of the soil microorganisms in the enumerated classes. Myxomycetes and protostelids were recovered from only 26 of the 81 soil samples. Their presence was correlated with levels of Ca2+, K+, and organic matter, and they were recovered from acidic soils and from soils in regions subject to acid deposition. Characteristics of soils that yielded cellular slime molds and myxobacteria were also analyzed.Key words: myxomycete, dictyostelid, myxobacteria, pH, acid deposition, soil organisms.

ISSN:0008-4026    

DOI:10.1139/b94-097

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Buried seeds ofOenothera biennis, which have the potential to form long-lived seed banks, were investigated to determine whether or not they (i) undergo seasonal changes in their dormancy states and (ii) require light for germination. Seeds were buried in soil and exposed to natural seasonal temperature changes. Samples of seeds were exhumed at monthly intervals for 31 months and tested for germination in light and darkness at 12-h daily thermoperiods of 15:6, 20:10, 25:15, 30:15, and 35:20 °C. At maturity in autumn, seeds germinated to 84–95% in light at 30:15 and 35:20 °C, but to 0–69% at other test conditions. By late winter, seeds germinated to 95–100% at the five thermoperiods in light and in darkness. In summer and autumn, germination in light decreased at 15:6 °C, and in darkness it dropped to 0% at 15:6 °C and decreased at 20:10, 25:15, 30:15, and 35:20 °C. Following the second winter of burial, seeds germinated to near 100% at all thermoperiods in light and darkness. Thus, seeds exhibited an annual nondormancy – conditional dormancy cycle, being nondormant from midwinter to late spring and conditionally dormant in summer and autumn.Oenothera biennisis 1 of 10 species whose seeds live for 39–40 years or longer in soil and also have an annual conditional dormancy – nondormancy cycle. Seeds of six of these species, includingO.biennis, can germinate in darkness in spring or summer at simulated habitat temperatures. Therefore, a light requirement for germination is not necessarily a prerequisite for long-term survival of buried seeds, and something other than darkness prevents germination of seeds of some species buried in soil.Key words: seed banks, buried seeds, germination, dormancy cycles, light requirement,Oenothera.

ISSN:0008-4026    

DOI:10.1139/b94-098

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

As an intact clone (one genotype) ofTrifolium repens(white clover) grows through a sward, parts of the stolon decay and fragments (ramets) are transplanted into different microenvironments. This common garden study was done to assess the impact this placement has on further development and growth of the new ramets. Genets ofT.repenswere sampled from each of four origins: from areas in an old pasture dominated byDactylis glomerata,Holcus lanatus, andLolium perenne, and from seed.Trifoliumfrom each origin was transplanted into each of three grass beds (Dactylis,Holcus, andLolium) with three replicates. Cuttings were taken annually for 4 years from all the clovers, transplanted into pots, grown for 10–15 weeks, and a number of morphological characters were measured. There was little indication that individuals ofTrifoliumgrow best in their "home" neighborhoods. Most variation in the data was the result of within-genet variation, i.e., phenotypic plasticity, a response assuring survival in environments that vary over time and space. The effects of grass neighbors onTrifoliumis mainly expressed as size differences and the effect of origins and genets mainly as differences in shape. The latter is due, in part at least, to different growth rates of parts relative to each other, the former to all growth rates being modified in a similar fashion. Because origins and genets have a longer history than treatments, these results argue for an evolutionary sequence of first size followed by shape differences.Key words:Trifolium repens, phenotypic plasticity, development, neighborhood effects.

ISSN:0008-4026    

DOI:10.1139/b94-099

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Polyamines were localized in embryogenic callus cells ofPicea glaucaby the fluorescent dyeo-phthalaldehyde and polyclonal antibodies raised against putrescine, spermidine, and spermine. Localization by both methods showed higher levels of polyamines in the nuclei and nucleoli than in the cytoplasm. In contrast with previous reports on cytochemical localization of polyamines in animal cells, stain was always excluded from the condensed chromatin of spruce somatic embryo cells.Key words: polyamines, cytochemistry, immunolocalization, white spruce.

ISSN:0008-4026    

DOI:10.1139/b94-100

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In this study we tested the prediction that male gender allocation in natural populations of common ragweed (Ambrosia artemisiifoliaL.) depends more on relative plant height within the neighbouring canopy than on absolute plant height. This is consistent with the assumption that success as a pollen donor for an anemophilous plant within a crowded population will be greater when neighbours are shorter than when neighbours are taller. Data on height and proximity of neighbours, irradiance, and target plant height, biomass, and gender allocation were collected from two natural populations. In one population, these data were also recorded for a group of target plants that had local neighbours artificially removed when the target plants were seedlings. Allocation to male flowers was most strongly positively correlated with height relative to that of close neighbours and with percent irradiance in natural populations. Numerous all-female plants were recorded among the smallest individuals that were suppressed by a dense overhead canopy of neighbours. No relationships were found between plant size and gender when plants were taller than their neighbours or when neighbours were artificially removed. Hence, previously reported size-dependent gender variation in this species may depend on the presence of neighbours. It is postulated that ragweed individuals may sense the presence of neighbours through the phytochrome system, and that effects of neighbours on light quantity and quality cues a shift to increased female function. However, plants that grew from the seedling stage without neighbours were heavier and more female but were not taller than plants with neighbours left intact. The interpretation of this effect is unclear but may reflect a change in plant architecture corresponding with the removal of neighbours.Key words: gender, plant height, plasticity, pollen dispersal, phytochrome, shading.

ISSN:0008-4026    

DOI:10.1139/b94-101

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Experimental spring-flooded and nonflooded water regimes were applied to prairie marshes dominated by whitetop grass (Scolochloa festucacea) in Manitoba, Canada, to examine their effects on aboveground and belowground primary production and to evaluate flooding management for wild hay production. Spring flooding increased marsh aboveground and belowground production. Annual and perennial forbs comprised a greater portion of aboveground production in nonflooded marsh. Two methods (soil coring and ingrowth into mesh bags) showed earlier commencement of belowground growth and greater belowground production in flooded marsh. Higher rhizome ingrowth in flooded marsh indicated that spring flooding increased plants' ability to replenish belowground reserves. The percentage of plant production allocated aboveground was greater in flooded marsh, but shifts in allocation were small compared with the absolute increases in production caused by flooding and could not account for the observed differences in aboveground production between flooding regimes. The strong plant growth response to flooding indicates that management that conserves or mimics the natural spring-flooded hydrologic regime can increase whitetop forage production and control invasion by undesirable species.Key words: belowground, hydrologic regime, prairie marsh, primary production, rhizomes, roots.

ISSN:0008-4026    

DOI:10.1139/b94-102

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

An unknown fungus isolated from an elm branch and inhibitory againstOphiostoma ulmiin vitro is described asPhaeotheca dimorphosporasp.nov. This dematiaceous deuteromycete propagates by endoconidia released after exfoliation of chlamydospore outer wall, as in mother cells of the type speciesPhaeotheca fissurella. However,P.dimorphosporadiffers from the type species by producing hyaline secondary ameroconidia between the endoconidial masses. Other ameroconidia, similar to the secondary ameroconidia, are produced through the chlamydospore outer wall. The optimal growth temperature ofP.dimorphosporais 23 °C, whereas it is 15.5 °C for the type species. On media containing a high dextrose concentration (30 g ∙ L−1), colonies ofP.dimorphosporaare gray and crustose and grow slowly, at least initially. Conversely, on media with a low dextrose concentration (5 or 10 g ∙ L−1) colonies have a faster growth rate and appear whitish or ivory and fluffy.Key words:Phaeotheca dimorphospora, diagnosis, inhibition, Ophiostoma ulmi, Dutch elm dise

ISSN:0008-4026    

DOI:10.1139/b94-103

出版商:NRC Research Press    

年代:1994

数据来源: NRC