摘要:

In the last decade, the study of mutants defective in floral development has contributed significantly to our understanding of floral evocation and morphogenesis. Genes inArabidopsis thalianaandAntirrhinum majusthat play key roles in (i) the transition from the vegetative to reproductive phase, (ii) the activation of floral development in specific shoots, and (iii) the unique arrangement of floral organs have been identified genetically and in many cases cloned. Many of the genes appear to encode transcription factors that act to select specific developmental programs of division and differentiation for groups of primordial cells. Other genes may be involved in detecting environmental conditions and transducing the signal to the developing meristems. Key questions remaining include how the regulatory proteins are produced in specific temporal and spatial patterns, interact with each other and initiate specific morphological programs. Although current research on floral morphogenesis has been limited to only a few species there is growing evidence that the basic processes are common to all flowering plants.Thus the information and tools currently being generated should be useful for studying a wide variety of flowering species. It seems reasonable to predict that within the next decade, we should have a fairly complete understanding of the basic mechanisms underlying floral morphogenesis and its evolution among the angiosperms.Key words:Arabidopsis thaliana, floral morphogenesis, molecular genetics.

ISSN:0008-4026    

DOI:10.1139/b95-105

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The location of an endogenous α-amylase/subtilisin inhibitor in developing and germinating barley (Hordeum vulgare, cv. Bonanza) was determined using immunohistochemical techniques. The inhibitor was found within protein bodies of cells containing starch granules in the starchy endosperm and embryo of developing caryopses. It could be detected as early as 2 weeks postanthesis in both organs. Upon germination, inhibitor was released from protein bodies, resulting in increased detection of the protein in regions of the starchy endosperm in which storage mobilization was occurring. Antibodies to α-amylase revealed large quantities of this protein in the same regions.Key words: α-amylase, α-amylase/subtilisin inhibitor, barley, germination, kernel development, starch.

ISSN:0008-4026    

DOI:10.1139/b95-106

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The roots of 11 epiphytic fern species from the generaElaphaglossum,Peltapteris,Hymenophyllum,Grammitis, andLellingeriawere studied by means of light and electron microscopy. All species showed a similar association with an ascomycete that traversed the root hairs and formed intracellular hyphal coils within cytoplasmic epidermal and outer cortical cells. The unbranched fungal hyphae were of a uniform diameter. They were surrounded by a flocculent matrix material and by the host plasmalemma. Cytoplasmic hyphae also occurred within degenerated host cells. The host–fungus interaction showed similarities to Ericoid mycorrhizae.Key words: ferns, mycorrhiza, ascomycete, ultrastructure, Costa Rica.

ISSN:0008-4026    

DOI:10.1139/b95-107

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The concepts of ecosystem health and ecosystem integrity are discussed and found to be ecologically inappropriate. The phrase ecosystem health is based on an invalid analogy with human health requiring acceptance of an optimum condition and homeostatic processes maintaining the ecosystem at a definable optimum state. Similarly, ecosystem integrity is not an objective, quantifiable property of an ecosystem. Health and integrity are not inherent properties of an ecosystem and are not supported by either empirical evidence or ecological theory.Key words: ecosystem health, ecosystem integrity, ecosystem, management, sustainability.

ISSN:0008-4026    

DOI:10.1139/b95-108

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Three strains ofChalara elegansfrom diverse geographical areas that contained multiple (4 or 5) double-stranded RNA fragments were compared with spontaneously derived cultures from these strains that were either partially cured or completely free of dsRNA. In the wild-type strains, presence of the dsRNAs was found to significantly enhance phialospore production and pigmentation of colonies, whereas radial growth and mycelial dry weight accumulation were reduced. The rate and overall percentage of phialospore germination on 1% Noble water agar were also significantly reduced by the presence of the dsRNAs. In two partially cured strains (only one 2.8-kb fragment remaining), pathogenicity to various plant tissues was significantly enhanced when compared with the wild-type strains containing multiple dsRNA. However, survival in field soil was enhanced in one strain and reduced in the other. In the completely cured strain, the loss of multiple dsRNA fragments was associated with enhanced growth, reduced phialospore production, and a complete loss of pathogenicity and capability for survival in soil. These results indicate that the effects of dsRNAs inC.elegansvary with the strain. In general, the presence of multiple dsRNAs in this fungus enhanced sporulation, altered colony morphology, and reduced growth and pathogenicity. However, since the complete loss of dsRNA was found to eliminate pathogenicity and reduce survival, it suggests that some dsRNA fragments inC.elegansmay confer an advantage to this soil-borne facultative plant pathogen.Key words: black root rot, soil-borne plant pathogen,Thielaviopsis basicola.

ISSN:0008-4026    

DOI:10.1139/b95-109

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Fresh collections ofCeriosporopsis sundicaenabled an ultrastructural study of ascospores and spore appendage ontogeny. Ascospores are surrounded by an exosporic mucilaginous sheath of variable morphology, initially "slug-shaped" but at maturity ovoid. The fibrous component of the appendage is contiguous with the mesosporium through discontinuities in the episporium. Polar appendages are extensions of the sheath and not discrete mesosporial outgrowths as characteristic ofCeriosporopsisspp. A reexamination of the type material ofC.cambrensisshows that spore measurements differ from those given by an earlier researcher, as does the general morphology of the appendages. It is concluded that two species are involved andC.cambrensismust be regarded a nomen dubium.Key words: appendages,Ceriosporopsis, Halosphaeriaceae,Limacospora, taxonomy, ultrastructure.

ISSN:0008-4026    

DOI:10.1139/b95-110

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The value of wetland is now widely recognized; some legislation requires "no net loss" of wetlands, although economic incentives still exist for wetland conversion. Rare plants may be protected by law; however, wetlands are rarely managed specifically to conserve rare species. Furthermore, it is not always clear how the environment should be manipulated to increase the abundance of such species, since necessary autecological details are rarely available. Species conservation involves demographic and genetic elements, as well as ethical decisions about the merits of transplanting or importing genes through controlled pollinations. Rare species may serve as indicators of habitat quality, although this will depend on the reasons behind the species' rarity. There is a need for multiple-use management plans that incorporate species- and habitat-conservation goals and that implement overall strategies to maintain or enhance the total quantity and quality of wetlands.Key words: rare plants, management, wetland conservation, habitat conservation.

ISSN:0008-4026    

DOI:10.1139/b95-111

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Caulonemata of the mossFunariawere examined to determine whether they are gravitropic.FunariaandPhyscomitrellawere also evaluated to compare amyloplast sedimentation with that ofCeratodon. Protonemata were either chemically fixed in place or examined alive using infrared time-lapse videomicroscopy.Funariacaulonemata were found to be negatively gravitropic, i.e., they grew upwards in the dark. Upward curvature reversed temporarily before cytokinesis inFunaria, a phenomenon already known forCeratodonandPhyscomitrella. Most horizontal and upward-curvingFunariatip cells contained a broad subapical zone where plastid sedimentation occurred. In dark-grownPhyscomitrellacaulonemata, sedimentation was detected by the presence of a thin, amyloplast-free strip of cytoplasm at the top of the cell. These results suggest that gravitropism and subapical amyloplast sedimentation may be relatively common in moss caulonemata.Key words:Physcomitrella, moss, protonema, plastid, sedimentation, gravity.

ISSN:0008-4026    

DOI:10.1139/b95-112

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Long-distance seed dispersal figures prominently in most plant conservation biology arguments, yet we possess little more than anecdotes concerning the relationship among deposition (seeds/m2), source strength (seeds/m2), and distance. In this paper we derive two simple models for long-distance deposition. The models are tested at the scale of 100–1600 m from the source and found to be within 5-fold of the observed deposition. There is no discernable decline in deposition for the range 300–1600 m. While we hesitate to extend model predictions to greater distances, both the models and the empirical results allow us to assert that rare wind-dispersed species in woodlots (dispersal distance around 1 km) are effectively isolated from one another at the temporal scale of 1000 years.Key words: plant conservation biology, wind dispersal of seeds, metapopulations.

ISSN:0008-4026    

DOI:10.1139/b95-113

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Sporoderm development is described inCucurbita pepo, a species characterized by large spinous pollen grains covered by pollenkitt; i.e. the degeneration product of the tapetum. During the tetrad stage, separate types of primexine are observed for microspines and macrospines. At maturity these spines are affected differently by acetolysis: microspines contain polysaccharides as well as sporopollenin, and macrospine contain only sporopollenin. Unlike other species investigated so far, the intine begins to form at the early microspore stage and is very complex in the pore area where it forms a Zwischenkörper. The pore is covered by a protein layer of sporophytic origin and by the operculum. Just before anther opening, the pore protrudes, exposing part of the poral intine. Mature pollen has a thin callosic wall. The findings are discussed in the light of the fact thatCucurbita pepopollen does not dehydrate prior to anthesis.Key words:Cucurbita pepo, pollen, sporoderm, exine, intine, sporophytic proteins.

ISSN:0008-4026    

DOI:10.1139/b95-114

出版商:NRC Research Press    

年代:1995

数据来源: NRC