摘要:

The leaf blade ofPisum sativumL. possesses proximal leaflets and distal tendrils and is altered by two recessive mutations that affect pinna identity,afila(af) andacacia/tendrilless(tl). Using morphological and histology features we characterized the variation in leaf form and pinna anatomy of theAfandTlheterozygous genotypes. Our goal was to identify the specific interactions of these genes and the relative influence of each in regulating all structural components of the leaf and pinna phenotypes. TheTl/tlgenotypes possess broad tendril - narrow leaflets in the distal region that are histologically more similar to leaflets than to tendrils. TheafafTltlleaves have simple tendrils in the distal region and branching complexity that is intermediate between that ofaftlandafleaves in the proximal region. Only the most distal tips are slightly expanded. Because theAfandTlgenes interact to affect almost all aspects of leaf and pinna form, they affect development at multiple levels of organization.Key words:acacia,afila, Fabaceae, leaf morphology, leaf anatomy,Pisum sativum.

ISSN:0008-4026    

DOI:10.1139/b99-030

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Most of the ice-free lands within the Canadian High Arctic are classified as polar desert (44%) or semidesert (49%). Much of this desert landscape supports no more than 6-10 vascular species that provide 1-3% cover and cryptogamic organisms that occupy 0-5% cover on the soil surface. The barrenness of these lands results from a short growing season and low summer temperatures that limit plant growth and the production of viable seeds. Limited areas have a 50-80% cover of cryptogamic crust and an 8-12% cover of vascular plants. These are areas in which surfaces remain moist for considerable periods in summer from snowflush waters. Where such cryptogamic soil crusts develop, they play a central role in soil development and nitrogen fixation. The two major components of this study were (i) an examination of fundamental reproductive, establishment, and growth characteristics of polar desert plants in the field and (ii) the relationship of these characteristics to environmental conditions in areas with and without cryptogamic crusts. Summer conditions during the study ranged from unusually warm (1991; 252 degree-days) to unusually cool (1992; 123 degree-days) with two average years (1994 and 1995; 172 and 166 degree-days, respectively). Differences in reproduction and establishment among these summers included (i) higher germination ability of seeds produced in the warm summer (1991) compared with more average summers (1994 and 1995) and (ii) significant seedling occurrence only in the average summers of 1994 and 1995. Seedling densities were much higher at crusted (206 seedlings/m2) than noncrusted sites (26 seedlings/m2). In both sites, root elongation of seedlings and older plants were significantly greater than shoot elongation, yet in established plants, shoot biomass was much greater than root biomass (root/shoot ratios from 0.1 to 0.3). Reproductive attributes varied among the species examined.Saxifraga caespitosaL. produced much smaller seeds thenDraba corymbosaR. Br. ex DC. andPapaver radicatumRottb., but the largest seeds ofS. caespitosa(produced in the warm summer of 1991) had much higher germination rates than any seeds of the other species. Based on an analysis of population age structures, seedling survivorship was low for all species but was especially low forS. caespitosa, despite its higher germination rates. All species were slow to germinate, with isolated seeds under ideal controlled conditions requiring a minimum of 20-30 days at a 20°C day and 15°C night. Seed germination in excised soil blocks under comparable conditions averaged 36-48 days. We believe these polar desert plant species lack special attributes to uniquely exploit the environment of these very stressful locations. Rather, they are simply adept at surviving the rigors experienced there. The same species grow much larger, flower and fruit more abundantly, and produce more viable seeds in high arctic environments more favorable than polar deserts, such as lowland polar oases (e.g., Truelove Lowland, Devon Island, Canada). Within the harsh polar desert landscape of the High Arctic, the presence of a cryptogamic crust that retains surface moisture, prevents soil churning, and includes nitrogen-fixing organisms provides a more favorable habitat for plant reproduction, establishment, and growth.Key words: High Arctic, plant reproduction, plant establishment, plant growth, cryptogamic crust, polar desert, Devon Islan

ISSN:0008-4026    

DOI:10.1139/b99-031

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Plants of the myco-heterotrophicBurmannia tenellaBenth. form star-shaped root systems consisting of 0.7-2 mm thick, succulent, brittle roots, reaching lengths of up to 3 cm. In cross section the roots consist of an epidermis, about 10 layers of parenchymatous cortex cells, an endodermis with U-shaped secondary cell wall depositions, and a very reduced central cylinder with two to five central xylem elements and two opposite phloem strands, surrounded by a pericycle of relatively large cells. Based on the thick, aseptate, intracellularly coiled hyphae, arbuscules, and the frequent vesicles, the fungal association ofB. tenellais considered to be aParis-type arbuscular mycorrhiza. The morphological and anatomical structures of the root are discussed in the context of the mycorrhizal dependency ofB. tenella. In some root samples, a second fungus with septate hyphae colonized the cortex intracellularly. This fungus restricts the spread of the aseptate symbiont without causing morphological changes to the cortex cells.Key words: Burmanniaceae, root morphology, root anatomy, arbuscular mycorrhiza, myco-heterotrophy, neotropical.

ISSN:0008-4026    

DOI:10.1139/b99-034

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The colonization processes of the xylem in the susceptible carnation cv. Early Sam and the resistant cv. Novada were studied ultrastructurally following inoculation withFusarium oxysporumf.sp.dianthi. Samples from 1 to 3 cm above the incision were collected over 5 weeks and processed following conventional procedures as well as with probes for cellulose,N-acetyl-glucosamine, and pectin. The fungus grew profusely in the vessel lumina of the susceptible cultivar. Some of the colonized vessels were lined with coating material connected to the fungal cell wall and extending into the host cell wall through microfilamentous-like structures. Coatings did not label for pectin or cellulose. The pathogen crossed from one vessel element to another (and at times to parenchyma cells) usually directly through pit membranes; often the invading structures of the fungus appeared to be either only membrane-bound or formed solely of microfilamentous-like entities. The fungus subsequently invaded extensively, generally by means of microhyphae, the vessel intercalary walls from the pit membranes and vessel wall junctures. Microhyphae had thin or imperceptible walls and contained only some of the normal cytoplasmic components. Initially, the invading hyphae dislocated the host cell walls, apparently mechanically more than by lysis; however, more pronounced lysis occurred following general tissue invasion. Host parenchyma cells seemed relatively unaffected, even after the surrounding walls had undergone severe degradation. Colonization of resistant plants was restricted. Degradation of tissues did not occur and microhyphae were not observed. Inoculated vessel elements in the 'Novada' plants contained numerous fungal cells and little occluding material, whereas the surrounding vessels were almost completely occluded. The initially invaded xylem became tangentially compartmentalized by parenchyma cell wall thickenings and by hyperplastic parenchyma. Occasionally, hyperplastic tissues were slightly re-invaded, forming secondary invasion pockets. Vessel-occluding material varied in structure and opacity, not only from vessel to vessel but also within the same vessel, and contained microfilamentous-like structures and other types of fine fibrillar material. Some vessel elements in or near the secondary invasion pockets contained only the finer fibrils that reacted strongly with an antibody specific for pectin. Vessel elements rarely contained tyloses.Key words: cellulose, chitin,Dianthus caryophyllus,Fusariumwilt, gels and gums, host wall degradation, microhyphae, pectin, tyloses.

ISSN:0008-4026    

DOI:10.1139/b99-033

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Genetically determined rules underlying black spruce (Picea mariana(Mill.) BSP) morphological development were revealed by using tree architecture analysis. Black spruce develops according to Rauh's model. Its relatively simple and well-hierarchized architecture comprises four categories of axes (A1-A4) and three distinct branching levels. First- and second-order axes (the trunk and branches) are monopodial, orthotropic structures with rhythmic growth and branching, and an unlimited life-span (or only limited by tree longevity). They are mainly devoted to spatial exploration and occupation. AxesA3andA4are monopodial, plagiotropic structures with a limited life-span, which are devoted to assimilation and reproduction. Female cones develop in terminal position onA3,whereas male reproductive structures develop in terminal or lateral position onA4. Reiteration (or duplication of axes) capacity is an important feature of the architecture of black spruce. Adaptive reiteration processes allow trees to renew their foliage and to reproduce vegetatively through layering. Traumatic reiteration processes tend to restore the tree's original architecture by replacing injured axes or parts of axes. In both cases, replicas originate from dormant buds located at the bottom of growth units (deferred or proleptic reiteration) or from growing axes (immediate or sylleptic reiteration).Key words: black spruce, growth form, tree architecture, architectural model, reiteration processes.

ISSN:0008-4026    

DOI:10.1139/b99-022

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

TenArmeria maritima(Mill.) Willd. populations (2n= 18) from contrasting ecogeographic situations were compared using 30 morphometric characters of karyotype and frequencies of abnormal metaphase and interphase cells in root-tip meristems. Despite the general symmetry and similarities, karyotypes of populations can be distinguished using a set of precise karyotypic features. Variations within populations mainly concerned the occurrence of satellites and weakly condensed areas of chromosomes. Total chromosome length measurements were congruent with flow cytometry estimates of DNA amounts. The geographical differentiation of European population karyotypes is in accordance with previously defined biochemical clustering. One population from Germany (ssp.bottendorfensis) is more similar to the American population (ssp.californica) than to the other European populations. Proposed trends of karyotype evolution are discussed in comparison with previous results on other character sets and taxonomic treatments. The species karyotype seems particularly unstable, as chromosome strong links at mitosis cause breaks generating chromosomal mutations and aneuploidy at the intra-individual level in all the populations. Abnormal interphase cells were found in most of the populations but were especially frequent in heavy-metal tolerant populations. The highest frequencies of karyotype aberrations were found in the American population and in populations adapted to soils with high levels of heavy metals or salinity. The frequency of interphase aberrations appeared to be related to the mean level of heavy-metal tolerance of populations. Consequently, the two types of abnormalities may originate from independent mechanisms. The genome behaviour ofA. maritimais discussed with reference to recent findings concerning the effects of soil toxicity on plant genomes.Key words:Armeria maritima, karyotype, population differentiation, soil stress tolerance, mitotic aberrations, abnormal nuclei.

ISSN:0008-4026    

DOI:10.1139/b99-028

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Using the continental-scale collections of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program, we examined selected members of the family Gomphonemataceae to expand the current state of knowledge of diatom taxonomy, morphology, and distribution. Ten taxa in the generaGomphonema,Gomphoneis, andGomphospheniaare examined. The taxonomic status of two taxa is revised, and one new species is described. Two new features are described for the genusGomphonema: slit-like areolae and ridge-like flaps or flanges on pseudosepta. Many North American gomphonemoid species appear to be restricted to certain geographic regions; the differences between western and eastern North America are striking. Trained analysts have had difficulty identifying and discriminating many of these taxa. We believe that this difficulty, in large part, results from our poor knowledge of the North American flora. Large-scale monitoring programs such as NAWQA, when teamed up with research organizations with common interests, hold great promise to expand our knowledge of the biodiversity of North American ecosystems.Key words: biogeography,Gomphoneis,Gomphonema,Gomphosphenia, National Water-Quality Assessment (NAWQA) Program, taxonomy; ultrastructure.

ISSN:0008-4026    

DOI:10.1139/b99-007

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Transversely ridged rodlets (Aristolochia-type) are of high systematic significance characterizing the ancestral Aristolochiales, Magnoliales, and Laurales. Sporadically, they also occur in various unrelated derived taxa. The ultrastructure, chemistry, and recrystallization of epicuticular waxes of nine species were investigated by high resolution scanning electron microscopy, gas chromatography, and mass spectrometry. Chemical analyses show that transversely ridged rodlets clearly differ in their composition. Waxes of one group are characterized by ketones, whereas a second group completely lacks ketones and is dominated by alkanes. Hentriacontan-16-one (palmitone) was found to be characteristic for transversely ridged rodlets ofAristolochia,Laurus, andPaeonia. Standard solutions were taken for recrystallization experiments under different conditions of solvent, crystallization velocity, and temperature. It was shown that transversely ridged rodlets or related crystals grow from total waxes of all species but never crystallize from individual compounds such as alkanes or palmitone. We concluded that transversely ridged crystals are formed by self-assembly based on a slow crystallization process and the presence of additives. This paper shows that transversely ridged rodlets occur convergently within angiosperms based on a similar mode of crystallization but a different chemical composition. The role of palmitone as a chemotaxonomic character of ancestral angiosperms is discussed.Key words: plant cuticle, epicuticular waxes, chemistry, ultrastructure, recrystallization, systematics.

ISSN:0008-4026    

DOI:10.1139/b98-229

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

This study documents changes in community and functional group across environmental gradients sensitive to climate warming in boreal permafrost peatlands and describes how future changes in temperature and precipitation may lead to changes in species composition and ecosystem properties. At the landscape scale, the presence of permafrost strongly influenced species composition. The position of permafrost thaw affected surface water pH and species composition. At local scales, a combination of water table depth and vegetation structure strongly controlled community composition. Permafrost plateau plots with highPicea marianabasal area were characterized by darker and drier understorey conditions, low cover ofSphagnumfuscum,Ledum groenlandicum, and lichen, and high cover of feather mosses. Aquatic collapse scar plots were dominated by aquaticSphagnumandCarex, whereas more xeric plots were dominated by hummockSphagnumand ericaceous shrubs. Functional group responses indicated that changing environmental conditions with climate warming may have significant impacts on community composition and ecosystem processes. A decomposition example is presented to show how changes in species and functional group composition could have important implications for ecosystem-level processes like peat accumulation during climate warming.Key words: bogs, fens, boreal, permafrost, vegetation, ordination

ISSN:0008-4026    

DOI:10.1139/b99-008

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Pollination can be a major factor influencing reproductive success in plants. Pollination may be influenced by variability in pollen production and vector activity associated with environmental heterogeneity in time and space. These factors were addressed experimentally using hand pollinations ofErica multifloraL., a shrub occurring in the western Mediterranean Basin that exhibits a long flowering period. Variation in pollen limitation was considered three times (early, peak, and late) over the flowering season and between two habitats (shrubland and pine forest). The breeding system and the pollination vectors were also studied by hand pollination and exclusion experiments. Xenogamy and natural pollination (control) treatments produced more seed and fruit set than geitonogamy and autogamy treatments. Insect visitors were less abundant at the end of the flowering period and in the pine forest habitat. Pollen limitation was not different between habitats, but it changed over the flowering period. Fruit set was pollen limited at the early flowering time, when less flowers were available. Both seed and fruit set were pollen limited at the late flowering time, when both flower density and insect visitors were lower. Seed and fruit set were not pollen limited at the peak of the flowering period, but their low values suggest resource limitation associated with a large number of developing fruits.Key words: breeding system, fruit set, hand pollination, insect pollinator, phenology, seed production.

ISSN:0008-4026    

DOI:10.1139/b99-015

出版商:NRC Research Press    

年代:1999

数据来源: NRC