ISSN:0008-4026    

DOI:10.1139/b00-003

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A physical barrier exists inVitis viniferaL. (wine-quality grapevines) between the canes that freeze at subzero temperatures and the buds that supercool, thereby avoiding ice formation in these delicate organs. Our objective was to characterize the ice nucleation barrier by observing grape buds at different stages of acclimation, by treating them with pectinase, and by comparing them to buds of the more hardyVitis ripariaL. and to non-supercooling buds ofPopulus nigraL. "Italica." Differential thermal analysis (DTA) indicated that asV. viniferaandV. ripariaacclimated in the autumn, the ice nucleation point of the buds declined, then increased as the grapevines de-acclimated in the spring. Laser scanning confocal microscopy was used to detect the penetration of fluorescent rhodamine green dyes from the cane into the bud as a measure of apoplastic permeability. These pore size exclusion tests indicated that the bud axes were impermeable to a 3000 MW dextran-conjugated dye when the ice nucleation temperature was below -20°C, but permeable above -20°C. This lower porosity presumably restricts the penetration of ice into the bud from the cane. In contrast to the twoVitisspecies, the permeability ofPopulusbuds did not limit ice propagation, and the water in buds froze between -5 and -10°C according to DTA. Pectinase and phosphate treatments of grape buds to remove pectin increased apoplastic permeability, increased the ice nucleation temperature, and prevented supercooling according to DTA. Light microscopy indicated that suberin coated the scales of the grape buds, probably preventing ice nucleation from the environment, but was not present in the bud axis region. We concluded that a permeability barrier, possibly containing pectin, in the axis of grape buds limits the propagation of ice into the buds and enables supercooling to occur.Key words: supercooling, freezing, acclimation, winter hardiness, pectin, confocal microsco

ISSN:0008-4026    

DOI:10.1139/b99-137

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Shoots were regenerated from leaf protoplasts of cytoplasmic male sterile and male fertile diploid sugar beet (Beta vulgarisL.) genotypes. Protoplasts cultured in Murashige and Skoog medium supplemented with 5 µM naphthaleneacetic acid, 2 µM 6-benzylaminopurine, 100 µMn-propyl gallate, and diamine putrescine at concentrations of 50, 100, or 500 µM were able to synthesize a new cell wall and entered successive mitotic divisions leading to the formation of callus colonies. Shoots were obtained via organogenesis by continuous culture of calli on the same basal medium supplemented with either cytokinin alone, or with a combination of cytokinin and auxin. The regenerants of both lines were characterized with regard to ploidy, and the regenerants of the male sterile line were further characterized with regard to possible somaclonal variation and organization of two mitochondrial genes:atpA andatp6. Chromosome counting revealed that tetra-, hexa-, and octa-ploids were present among regenerants. Random amplified polymorphic DNA (RAPD) analysis identified one somaclonal variant among 31 shoots tested, whereas hybridization with both mitochondrial probes showed no notable changes in the organization of mtDNA within these loci.Key words:Beta vulgarisL., protoplasts, regeneration, random amplified polymorphic DNA (RAPD),atpA,atp6.

ISSN:0008-4026    

DOI:10.1139/b99-145

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Sediment samples were collected from 77 lakes in the Mackenzie Delta representing a gradient of lakes from those having continual connection with the sediment-laden Mackenzie River to lakes having connection for only a couple of days every few years. Diatom assemblages in all lakes were dominated by a diverse benthic microflora, primarily from the generaNaviculaandNitzschia. Maximum relative abundance of the dominant taxon at all sites was less than 30%, and most taxa did not dominate in more than one or two lakes. Delta lake assemblages were distinct from diatom assemblages associated with other regional transects of upland tundra and forest lakes. Detrended correspondence analysis showed that nonmotile epiphytic genera, such asCocconeisandGomphonema, were more common in lakes having a lower influence from the Mackenzie River, reflecting the extensive macrophyte growth within these lakes. Species diversity decreased as macrophyte production increased. Taxa responses along this macrophyte production gradient were modeled using partial least squares regression. Diatoms were sensitive to the degree of river influence, and the related biological and limnological changes, suggesting assemblages can provide an indication of hydrological variability within Mackenzie Delta lakes.Key words: diatoms, detrended correspondence analysis, Mackenzie Delta, floodplain, lakes.

ISSN:0008-4026    

DOI:10.1139/b99-156

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Leaf trichome morphology and density are described for three species belonging to the genusTremafrom West Africa:T. africana(Planch.) Blume,T. orientalis(L.) Blume, andT. nitens(Hook. & Planch.) Blume. Leaves of specimens collected in West Africa were observed using scanning electron microscopy. Unicellular trichome morphology was assessed, and a 3 × 3 two-way contingency table analysis showed dependence between the trichome type and species identity. Density of unicellular and multicellular trichomes on both leaf surfaces as well as the number of cells composing the stalk of multicellular trichomes were measured and subjected to nonparametric analysis of variance. Kruskal-Wallis tests yielded significant results (p< 0.05) among the three species for all characters except unicellular trichome density on the adaxial leaf surface. Wilcoxon two-sample tests showed that all species were different, except for the density of multicellular trichomes on the abaxial leaf surface where densities inT. africanaandT. orientaliswere not significantly different. The number of cells composing the stalk of multicellular trichomes was significantly different among each species on the adaxial leaf surface, but on the abaxial one,T. africanaandT. orientalisexhibited no significant differences. The value of these characters in the discrimination between the three species is discussed.Key words:Tremaspp., Ulmaceae, West Africa, leaf trichomes, morphology, density

ISSN:0008-4026    

DOI:10.1139/b99-157

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

AsterlaurentianusFernald is an annual plant endemic to the St. Lawrence estuary. It typically grows in salt marshes at the periphery of shallow lagoons. In this habitat, the water level fluctuates greatly both within and between years. Such fluctuations may induce significant interannual variations in marsh-plant populations. In this study, we experimentally determined the effects of different water availability conditions, imposed at various stages of plant development, on the performance ofA.laurentianus. Waterlogging had no significant effect on net carbon assimilation rate, plant growth, and biomass allocation. However, a drought stress at the time of reproductive-bud differentiation had a negative effect on flower-head production. We propose that occasional reproductive failures resulting from late-summer droughts may cause significant interannual fluctuations in the size ofA. laurentianuspopulations, potentially making them more susceptible to local extinction.Key words:Asterlaurentianus, endemic plant, Îles-de-la-Madeleine, rare plant, salt marshes, water stress

ISSN:0008-4026    

DOI:10.1139/b99-158

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

We studied the vegetation patterns around cottongrass tussocks with varying characteristics in a cut-away peatland 20 years after abandonment. When the effect of water table level variation was eliminated, the remaining variation in vegetation was related to (i) tussock characteristics and (ii) distance and orientation from a particular tussock. Logit regression showed a positive interaction between distance from the base of a tussock and a tussock's sheltering properties for all the studied plant species, indicating that the smaller the tussock the nearer plants have to be to find a favourable microsite. A southerly direction, which is the most exposed to solar irradiation, was the most inhospitable microsite. Our results indicated that cottongrass tussocks may offer a variety of microsites for colonizers with varying ecological requirements.Key words: cut-away peatland, colonization,Eriophorum vaginatum, facilitation, logit models, ordination.

ISSN:0008-4026    

DOI:10.1139/b99-159

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Genetic variability among accessions of Russian thistle (SalsolatragusL.) from California was investigated using allozymes and DNA-based molecular markers. Aspartate aminotransferase and 6-phosphogluconate dehydrogenase displayed two multienzyme phenotypes that were widespread in plants throughout the state. Random amplified polymorphic DNA analysis was conducted on samples of the two isoenzymic phenotypes collected throughout California, as well as additional accessions from France and Turkey andSalsola paulseniiLitv. Six primers produced 23 polymorphic bands. Analysis of the patterns of bands by calculation of simple matching coefficients and cluster analysis confirmed the genetic distinctness of the two isoenzymic phenotypes ofS.tragus;S.paulseniiwas markedly different from both types. Mean fruit weights from plants grown under similar conditions were different between the two types as well. These results and preliminary cytological analysis together suggest that the two types are actually two different species ofSalsola, only one of which has been previously recognized. Analysis of the DNA-based markers suggests that one of the genetic entities may be closely related toSalsolafound in Europe, while the area of origin of the second entity is currently obscure.Key words: allozyme, genetic diversity, RAPD assay,Salsolatragus,Salsolapaulsenii.

ISSN:0008-4026    

DOI:10.1139/b99-160

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Deux clones de manioc, le clone Pétiolule Madagascar et le clone Pétiolule Congo présentent des feuilles dont la longueur du pétiole varie très fortement. Cette longueur est, chez ces clones, un marqueur de la vitesse de surrection du premier primordium foliaire. Chez ces deux clones, particulièrement chez le 'Pétiolule Madagascar', on observe la formation régulière d'entre-noeuds courts, insérés entre une feuille à pétiole court située au-dessous, et une feuille à pétiole long située au-dessus. Un raccourcissement temporaire de la longueur de l'entre-noeud est donc lié à une accélération de la surrection foliaire. Ce raccourcissement est déterminé lors de la première phase de l'élaboration de l'entre-noeud, qui s'effectue à la base du méristème apical, juste au-dessus du premier primordium. Il traduit une modification du fonctionnement de cette seule zone basale du méristème apical. La relation existant entre entre-noeud court et allongement du pétiole apporte quelques précisions sur les caractéristiques de la première phase de formation de l'entre-noeud, une phase particulièrement mal connue.Mots clés: manioc, entre-noeud

ISSN:0008-4026    

DOI:10.1139/b99-161

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Le hêtre a une croissance rythmique où chaque pousse annuelle est constituée d'une unité de croissance (u.c.) printanière parfois suivie, quelques semaines plus tard, d'une unité de croissance estivale. L'u.c. printanière présente une disposition foliaire alterne distique, tandis que l'u.c. estivale, selon certains auteurs, a une disposition foliaire alterne spiralée. Au terme d'observations morphologiques et histologiques de bourgeons formés à différentes périodes de l'année, il s'avère que la disposition foliaire du hêtre n'évolue pas d'un type d'u.c. à l'autre : les ébauches foliaires sont toujours disposées suivant deux droites parallèles, rapprochées sur un côté de la tige selon une disposition « plagiotrope distique ». La symétrie axiale d'une u.c. peut toutefois se modifier au cours de son allongement et évoluer d'une symétrie bilatérale vers une symétrie radiale secondaire. Cette évolution est le résultat d'une réorientation des nœuds par torsion des entre-nœuds, les plus grands déplacements d'organe foliaire étant réalisés par les u.c. les plus longues au niveau de leurs entre-nœuds les plus longs. Il est possible de rattacher degré de développement des u.c. et architecture des arbres. Les arbres les moins vigoureux (très jeunes ou situés sous couvert forestier dense) ont un axe principal plus ou moins incliné, constitué d'u.c. peu développées dont la symétrie est bilatérale; l'axe principal est plagiotrope et porte un houppier plan. En revanche, les arbres les plus vigoureux (adultes ou en situations forestières favorables) ont un axe principal vertical, constitué d'u.c. relativement longues et de symétrie radiale; l'axe principal est orthotrope et porte un houppier bien réparti tout autour de lui.Mots clés: morphol

ISSN:0008-4026    

DOI:10.1139/b99-162

出版商:NRC Research Press    

年代:2000

数据来源: NRC