摘要:

Within the last 3-4 years, evidence has accumulated to indicate that hemoglobin proteins exist widely in the plant community. This review presents some of the evidence to support this view and describes some of the properties of a barley hemoglobin. Barley hemoglobin has a strong avidity for oxygen, having an oxygen dissociation constant for oxyhemoglobin of 3 nmol L-1. It is induced under low oxygen tensions, with the induction regulated by ATP, or some consequence of ATP action. Experiments with transformed maize cells indicate that hemoglobin acts to improve the energy status of plant cells under low oxygen stress. It is postulated that hemoglobin acts as an oxygenase in plants. The review is a consequence of a CSPP Gold Medal Presentation at the Plant Biology 1997 Meeting in Vancouver, B.C.Key words: nonsymbiotic hemoglobins, hypoxia, barley, flooding tolerance.

ISSN:0008-4026    

DOI:10.1139/b98-057

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

One of the most obvious features on the foredunes and strands of coasts and lakes is recurrent burial in sand. Burial levels vary in different coastal sand dune systems and influence the physical and biotic microenvironment of the plant and soil. Foredune plants along coasts possess numerous adaptations to withstand burial. Studies show that below a certain threshold level of burial, the growth of all foredune plant species is stimulated probably because of multiple factors, namely improved soil resources, increase in soil volume, reactive plant growth, and enhanced mycorrhizal activity. However, as the level of burial increases, the positive response starts to decline until it becomes a negative value. For example, burial may reduce seed germination, seedling emergence, survival, and growth of seedlings and adult plants. At the community level, burial acts as a filter and selectively eliminates susceptible species, reduces the relative abundance of less tolerant species, and increases the abundance of tolerant and sand-dependent species. However, if sand deposition continues unabated, even the sand-dependent species are eliminated and a bare area is created. The emergence of a plant from a burial deposit primarily depends on the energy reserves in its storage organs and the speed, depth, and frequency of burial. Upon burial the plants shift resources from the belowground to the aboveground parts. Different plants show varied morphological responses to sand accretion. For example, the culms of grasses emerge by an increase in the number of nodes per culm and the elongation of internodes. Similarly, the emergent trunks and woody branches of tolerant trees and shrubs produce new buds and suckers at a higher level on the stem. In response to burial, the coastal sand dune species produce shootborne roots close to the new soil surface probably because of decreased oxygen levels.Key words: sand accretion, adaptations to burial, zonation of vegetation, burial of seeds, plant vigour, impact on communities, modes of emergence.

ISSN:0008-4026    

DOI:10.1139/b98-058

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Field observations and published data suggested that the oomycete parasiteAlbugo candida(Pers.) Kuntze could exist as latent, asymptomatic, systemic infections. The wild crucifer speciesLepidium campestre(L.) R.Br., Arabis lyrataL., andErysimum menziesiissp.eurekenseR.A. Price were chosen as models to test this hypothesis. Detection of the parasite in asymptomatic host tissue was based on polymerase chain reaction amplification of ribosomal DNA internal transcribed spacer region I ofA. candidausing primers designed to discriminate between plant and parasite DNA template.Albugo candidawas detected in high proportions of asymptomatic field plants (vegetative and reproductive), greenhouse grown vegetative rosettes, and laboratory germinated seedlings of each species. For example,A. candidaappeared to be systemic in all 20 field plants and 10 inoculated rosettes ofL. campestre.Albugo candidawas present in uninoculated rosettes and seedlings (up to 98%) suggesting seed borne transmission of the pathogen. Although the parameters controlling symptom development are still unclear, presence of the pathogen appeared not to be sufficient for symptom expression. Persistent, asymptomatic, systemic infections that are vertically transmitted through seed suggest thatA. candidamay possibly form endophytic relationships with at least some of its crucifer hosts.Key words: fungal endophyte, latent infection, PCR detection, rDNA ITS I.

ISSN:0008-4026    

DOI:10.1139/b98-039

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The first notable sign of shoot and root meristem development in zygotic embryos of white spruce (Picea glauca(Moench) Voss) was the appearance of starch in the respective poles of the embryo. Starch granules gradually accumulated in the subapical cells of the shoot pole and were soon followed by vacuolation in the subapical cells. Vacuolation reached its highest degree in these cells at the early embryo stage. With the formation of the large vacuolated cells, the surface cell layer at the summit of the shoot pole enlarged and differentiated into the surface initials of the shoot meristem. These cells were large with distinct nuclei. As the embryo matured, the large vacuoles within the subapical cells were replaced by small ones with a concomitant increase in the cytoplasmic density of the subapical cells. After germination, the surface initials remained distinct; however, the subapical cells had different fates depending on their location. The subapical cells located next to the surface initials became the central mother cells of the shoot meristem and those located near the cotyledon junction divided periclinally and gave rise to the epicotyl rib meristem. The remaining subapical cells near the procambium became part of the pith. In the root pole, starch could be found in the cap region terminating underneath the developing procambium at the club-shaped stage of embryo development. Two layers of root initials appeared at the junction between the developing procambium and the root cap. The initials were distinct as they were larger in size than surrounding cells. Cell division activity could not be detected in the layer of initials immediately next to the procambium, while mitotic activity could be seen in the adjoining layer next to the root cap. As the embryo matured, cells surrounding the root initials also took on structural characteristics similar to the root meristem initials. As a result, the region of the root meristem initials expanded in size, and the bilayered configuration became obscure. After germination, mitotic figures could be found in the root initials. As seedling continued to grow, fewer mitotic figures could be found in the root meristem cells adjacent to the procambium pole. In roots of mature plants, a group of isodiametric cells could be discerned between the procambium and the root cap. Mitotic activity was not readily detected within this group of isodiametric cells but mitotic figures could be found in surrounding cells.Key words: apical meristems,Picea glauca, white spruce, zygotic embryogenesis.

ISSN:0008-4026    

DOI:10.1139/b98-042

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The long-term effects of high nitrogen supply on the growth and partitioning of biomass in a common sedge species,Carex rostrataStokes, were studied in a greenhouse experiment. Special attention was paid to free amino acids and soluble sugars, representing biochemically available fractions of nitrogen and carbon, respectively, in the tissues ofCarex. Plants were grown in peat in buckets, and nitrogen was added as ammonium nitrate (2, 5, and 10 g N m-2year-1) five times during two growing seasons. Changes in biomass allocation patterns became evident towards the end of the second growing season. The biomass of shoots was highest in the high-N treatment, resulting in a high ratio of aboveground to belowground biomass. The high biomass of shoots was due to both the high density of current-year shoots and later senescence in the high-N treatment. No differences were observed in the belowground biomasses. Changes in allocation patterns were accompanied by changes in the soluble fractions of carbon and nitrogen. The concentration of free amino acids (FAA) was significantly higher (both shoots and roots) and the concentration of total nonstructural carbohydrates (TNC) lower (roots only) in the high-N treatment. The concentration of total nitrogen also increased with increasing supply of nitrogen. The results indicate that a high long-term supply of nitrogen may shift the internal carbon to nitrogen balance ofCarextowards higher availability of nitrogen. Compared with the carbon to nitrogen ratio, the TNC:FAA ratio seems to be a better indicator of the internal carbon to nitrogen balance. A low TNC:FAA ratio may enhance the allocation of biomass to shoots and also increase the density of shoots.Key words: amino acids, biomass partitioning, carbon,Carex, nitrogen, sugars.

ISSN:0008-4026    

DOI:10.1139/b98-046

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

In experiments conducted under controlled conditions, excision of the shoot ofElytrigiarepens(L.) Nevski increased the rate of rhizome elongation and promoted the growth of the lateral rhizome buds. Measurements with a transducer showed that the long-term growth response of the rhizome to shoot excision (4-6 days) was preceded by an immediate but transient (10 min) increase in growth rate. These various responses were associated with the occurrence of guttation from the rhizome apex, increases in the water content of the rhizome apex and lateral buds, and a 62% increase in rhizome water (pressure) potential. Parent shoot excision also induced a transition from rhizome to shoot development at the rhizome apex and caused lateral buds to develop as shoots instead of rhizomes when released from apical dominance. These developmental responses were associated with reductions in the dry weight of the rhizome apex and lateral buds and increases in the total N, amino-N, and nitrate content of the rhizome apex when expressed on a dry weight basis. These results provide evidence that, inE. repens, competition for water by the parent shoot may limit rhizome growth and contribute to the correlative inhibition of the lateral buds. They are also consistent with previous evidence that the C:N ratio may be an important morphogenetic factor in the mechanism controlling the path of bud and rhizome development.Key words:Elytrigia repens, water, nitrogen, rhizome, apical dominance.

ISSN:0008-4026    

DOI:10.1139/b98-049

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A laboratory technique was standardized for studying the release, maturation, germination, and pathogenicity of ascospores ofUncinula necator(Schw.) Burr. Surface disinfestation and wetting of grape (Vitis viniferaL.) leaf disks bearing cleistothecia collected in the vineyard before incubation in a humid chamber for 48 h at 20°C were found essential for obtaining the release of ascospores (8 ascospores/cm2). Storage conditions involving periodic wetting treatments of cleistothecia at 5°C during 110 days were necessary to induce both ascospore release (80 ascospores/cm2) and germination ability (62%). The matured ascospores were pathogenic on healthy leaf disks at 20°C indicating their probable role as a primary inoculum source. This technique can be helpful in studying the inheritance of characteristics such as pathogenicity and fungicidal resistance.Key words: cleistothecia, ascospores, maturation, germination, pathogenicity,Uncinula necator, grapevine, powdery mildew.

ISSN:0008-4026    

DOI:10.1139/b98-054

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

To characterize as early as possible the status of flowering differentiation in Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco), the variation of bound or conjugated polyamines is studied in the shoots of young plants (6 years old) during the period covering flowering initiation (between 30 and 75 days after bud burst). These compounds are also quantified in sexual and vegetative buds. The quantitative effects of treatments susceptible to stimulate the flowering (application of gibberellins and (or) calcium nitrate) on the level of conjugated polyamines are investigated in the shoots. The combination of gibberellins to calcium nitrate application strongly increases the flowering. Conjugated polyamines are particularly abundant in sexual buds and in the shoots of flowering plants. Sexual buds are also characterized by a ratio of conjugated putrescine to conjugated spermidine about four to six times higher than in vegetative buds. The accumulation of conjugated polyamines in the shoots accompanies bud sexualization, which suggests that conjugated polyamines may constitute potential markers of floral initiation in Douglas-fir.Key words: floral induction, flowering marker, conjugated polyamines, Douglas-fir.

ISSN:0008-4026    

DOI:10.1139/b98-044

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A previous polymerase chain reaction based survey for the occurrence of the intron in chloroplast generpoC1 revealed its absence in one of the eight species ofMedicago(Fabaceae; Trifolieae) examined. We extend the survey ofMedicagoto include 65 of the 86 species, representing all 12 sections and seven of the eight subsections recognized in the most recent comprehensive treatment of the genus. Our results indicate that 17 species from five sections lack the intron and that three of these sections are heterogeneous with regard to intron content. DNA sequencing across therpoC1 intron-exon boundary in three of these species reveals the precise excision of the intron from the gene. Phylogenies derived from nuclear ribosomal DNA internal transcribed spacer sequences, estimated using maximum parsimony and maximum likelihood methods, suggest that most of the previously recognized sections inMedicagoare not monophyletic as currently circumscribed. Furthermore, these results suggest that therpoC1 intron has been lost independently a minimum of three times during the evolution of the group. The occurrence of multiple independent intron losses severely reduces the utility of this character as a phylogenetic marker inMedicago.Key words:Medicago, Fabaceae, chloroplast DNA,rpoC1 intron, nuclear ribosomal DNA internal transcribed spacer (ITS) sequences.

ISSN:0008-4026    

DOI:10.1139/b98-047

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

This study analyzes plant material in a highUlex europaeusheath to provide information on the partitioning of this ecosystem for fire propagation models. The aboveground biomass, followed for 15 months, has a spatially heterogeneous distribution that is a result of the layered pattern of the various branches. This pattern creates an internal moisture gradient that decreases from the apex to the base of the plant. This gradient also varies according to the species phenology. New, green branches with a high moisture content are at the top of the plant (upper strata), whereas woody branches with a lower moisture content are found near the ground (lower strata). Dry branches and spines, which produce most of the litter, are homogeneously distributed throughout the plant. Temporally, the layered pattern is homogeneous through the year and thus creates a constant fire risk. Soil organic horizons are temporally, spatially, and compositionally heterogeneous. The L layer is always two to three times thinner and drier than the duff layer (F+H). The total depth, weight, and moisture content of the organic horizons vary considerably across both the plot and square metre scales. The distance from a plant has a significant influence on the depth distribution of the soil organic horizons. Fuel distribution on both the soil surface and the plant must be considered to understand fire behaviour in this ecosystem.Key words: architecture, biomass, fire, fuel, humus, moisture content.

ISSN:0008-4026    

DOI:10.1139/b98-045

出版商:NRC Research Press    

年代:1998

数据来源: NRC