摘要:

We investigated rate-regulating factors for decomposition rates of Scots pine needle litter at 22 sites over a 2000-km long transect ranging from the Arctic Circle in Scandinavia to northern continental Europe. We found very different patterns for rate-regulating factors in the early stages of decomposition as compared to later stages (> 20% accumulated mass loss). The initial decomposition rates (measured over the 1st year) ranged from about 10.9%/year close to the Arctic Circle to about 43.7%/year in south Sweden. The dominant rate-regulating factor was climate (average annual temperature, and actual evapotranspiration), and none of the substrate-quality factors was significant. In the later stages, the annual mass loss varied from 2.2%/year to 41.5%/year. The rate-regulating factors were climate and the litter's concentration of lignin. We found that the effect of lignin concentration on litter mass-loss rate varied with site and this relative effect was negatively related with actual evapotranspiration. The effect of lignin concentration on mass-loss rates near the Arctic Circle was thus low (at low values for actual evapotranspiration) whereas in Southern Sweden and on the continent the rate-regulating effect of lignin was higher.Key words: foliar litter, decomposition, lignin, climatic transect, rate-regulating factors, climate change.

ISSN:0008-4026    

DOI:10.1139/b95-163

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Peroxidases seem to play an important role in the regulation of auxin levels during the rooting of cuttings. In avocado, leaf peroxidase activity remained constant throughout the rooting process in the three fractions analyzed (soluble, ionically, and covalently bound to cell wall). Soluble peroxidase activity in stem basal parts increased twofold after 3 days and then remained constant until the end of the process. Cationic and anionic electrophoresis revealed a lower number of isoenzymes in the stems than in the leaves. Histological stainings at stem basal parts were also carried out to localize the enzyme activity. Peroxidase was active in all tissues at the time the cutting was taken, with vascular bundles and epidermis giving the strongest reactions. During the process of root formation peroxidase activity was closely associated with growth and differentiation processes, e.g., cambial cell division and xylogenesis; a strong reaction was also found in the developing root primordia. The possible role of peroxidases in the regulation of auxin levels during the rooting process in avocado is discussed.Key words: auxin, avocado, peroxidase, rooting.

ISSN:0008-4026    

DOI:10.1139/b95-164

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Spores ofFrankiastrain HFPCcl3 nodulatedCasuarina equisetifoliaafter passage through the digestive tracts of captive parakeets (Melopsittacus undulatus). Parakeets excreted infectious fecal material from 6 to 72 h after ingesting food inoculated withFrankiaspores. Air desiccation of spore-containing fecal material reduced its infectious capacity by approximately 90%. Hyphal filaments of this strain lost most of their infectious capacity after passage through parakeet digestive tracts. These results indicate that it is possible for spores ofFrankiato survive passage through the digestive tracts of birds, thereby predisposing them to avian dispersal.Key words: actinorhizal plants,Casuarina,Frankia, nodulation, parakeets, spores.

ISSN:0008-4026    

DOI:10.1139/b95-165

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Genetic variation inGremmeniella abietinaisolated fromPinus sylvestris,Pinus contorta, andPicea abiesin southern and northern Fennoscandia was studied with arbitrary primed polymerase chain reaction. FennoscandianG.abietinaisolates were clearly separated into two ecotypically distinct groups based on their amplified banding patterns. Analysis of variance based on amplified fragments, AMOVA, and principal component analysis confirmed the separation of the isolates into the two groups. One group contained isolates associated with a disease syndrome affecting young trees covered by deep snow during winter in northern Fennoscandia. The second group of isolates was found on trees between 15 and 40 years old, scattered throughout the crowns. It occurs throughout Fennoscandia but is most frequent in the southern parts. No size polymorphism was found in fragments resulting after restriction enzyme digestion of internal transcribed spacer and intergenic spacer regions of nuclear ribosomal DNA. An estimate of gene flow between populations calculated based on amplified band frequencies,FST, indicated that there was restricted genetic exchange between populations of the two groups of isolates.Key words:Gremmeniella abietina, arbitrary primed polymerase chain reaction, genetic variation, ecotypes, ribosomal DNA.

ISSN:0008-4026    

DOI:10.1139/b95-166

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

A histological study examined condensed tannin (CT) formation in plant tissue samples taken from the meristematic area of very young sainfoin (Onobrychis viciifoliaScop.) seedlings and from leaflets sampled at various stages of development in mature plants growing in the greenhouse. Light and electron microscopy revealed no CT in the seedling meristem and leaf primordia, but CTs were seen very early in leaf development forming first in the vacuoles of discrete cells of the abaxial subepidermal layer when the leaflets were recognizable, but still folded. Immature leaflets collected from the growing point of a mature sainfoin plant show similar CT formation with the abaxial cell vacuoles filled with CT when the new leaves have reached the 90°-fold stage. As the leaflets unfold and mature, CTs begin to appear in the vacuoles of small, but discrete cells in the adaxial subepidermal layer while the tannin-containing cells in the abaxial subepidermal layer begin to lose CT. The CT continues to increase in the adaxial layer until typical enlarged tannin idioblasts or sacs are observed at full leaflet expansion and maturity. By this stage, the vacuoles in the abaxial layer are almost empty. In senescing leaflet samples collected from the leaf rachis attached to the last and second to last node near the base of the plant, the cells in both subepidermal layers have lost the majority of the CT that was originally formed. At senescence all tannin-containing cells appear as empty shells. We speculate that a finite amount of CT is formed in the two subepidermal layers of new leaves at different stages of early leaf development, does not increase during the mature phase, and is catabolized in older leaves and during senescence.Key words: condensed tannins, sainfoin,Onobrychis viciifolia, leaf development.

ISSN:0008-4026    

DOI:10.1139/b95-167

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The chronology of fruit development and vegetative growth is described for the apricot cultivar 'Rouge de Roussillon'. We observed a synchrony between the major events of fruit development and those of vegetative growth. This allows us to complete a descriptioon of phases in fruit by taking in account the unfurling of preformed, then newly formed parts of growth units (GU). During the first period, which lasts approximately 12 days following full flowering, numerous events unfold simultaneously. In the absence of leaves, everything the tree produces during this period depends on its reserves. During the second period (from around 12 to 30 days) cell division ceases in the future fruit and the preformed parts of the growth units unfurl. From 30 to 60 days after full flowering, the fruit develops little, while the neoformed parts of the growth units are formed. The cessation of growth is spread out at intervals during this period and, at 60 days, 80% of GU have ceased to grow. The embryo continues its development until about 90 days, while the number of growing shoots is limited. Finally, beyond 90 days, the fruit finishes its enlargement while new growth units appear on the tree. The period of direct concurrence between vegetative and floral development seems limited to the two early periods. In effect, the preformed leaves in the winter bud seem to be incapable of providing assimilates to all the growing organs. Consequently, the priority is alternatively vegetative growth (unfurling of newly formed leaves) then fruit development.Key words: apricot, embryogenesis, growth, flowering, fruit development. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b95-168

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Acrotonie branching refers to the superior development of distal axillary shoots along the supporting branch. Although acrotony is quite common the underlying physiological mechanisms remain unknown. A careful study of the acrotonic growth habit of "géranium rosat" in various conditions allows one to distinguish three components. The first two are consequences of fixed gradients of growth potential that seem to set up at an early stage of ontogeny. They are tightly related to the morphogenetical sequence of initiation of the successive meristems. The third component is more variable and is probably related to competition for light due to mutual shading.Key words: branching, acrotony,Pelargonium, géranium rosat.

ISSN:0008-4026    

DOI:10.1139/b95-169

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

'Valencia' orange, a commercially important cultivar ofCitrus, forms polyembryonic seeds by an apomictic process called nucellar embryony in which many embryos initiate directly from nucellar cells surrounding the sexual embryo sac. We observed anther, ovule, seed, and fruit development in relation to nucellar embryo development in seeds and unfertilized ovules of 'Valencia'. Pollination and fertilization are required to set fruit in 'Valencia', and low seed set was found to be related to defects in both male and female gametogenesis. Nucellar embryo initial cells were evident histologically in ovules of flowers just prior to anthesis. However, in vitro culture of ovules from flowers at different prepollination stages showed that embryos could develop from ovules cultured as early as the binucleate stage of megagametogenesis in which nucellar initial cells were absent histologically. During fruit development, the timing and sequence of the early events of nucellar embryo formation were synchronous in seeds and unfertilized ovules, indicating a co-ordinated control of embryo development in spatially and developmentally distinct structures. In both developing seeds and unfertilized ovules, embryo initial cells first formed thick walls, which isolated them from surrounding maternal tissue. In later stages, the cell walls thinned in some initial cells and embryogenesis became asynchronous. Cleavage of embryogénie cells coincided with degenerative processes linked to embryo sac expansion in seeds and to a previously unreported, localized degeneration in the central portion of the nucellus in unfertilized ovules. Some initial cells never divided. Nucellar embryo development was restricted to the central portion of unfertilized ovules and to the micropylar region of seeds. Only fertilized ovules had the capacity to form mature polyembryonic seeds. In unfertilized ovules a specialized vascular structure formed linking developing embryos to the chalazal vasculature of the ovule. Embryo development arrested at the globular stage in unfertilized ovules and the integuments differentiated to form a seed coat. The timing of reproductive events described was linked to floral and fruit morphological characteristics to facilitate molecular characterization of nucellar embryogenesis and seed formation in this cultivar.Key words:Citrus, nucellar embryony, seed, ovule, apomixis.

ISSN:0008-4026    

DOI:10.1139/b95-170

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Principal components analysis, discriminant analysis, cluster analysis and two level nested analysis of variance were performed on 961 herbarium specimens ofArmeria maritimacovering the complete geographic range of the species in North America and Greenland. Among the monomorphic, self-compatible specimens combining coarsely reticulate pollen and papillous stigma, we recognized three subspecies. Along the Pacific coast from California to Vancouver Island, the single taxon ssp.californicais proposed, which includes the formerly described var.purpurea. In arctic and subarctic regions, ssp.sibirica, which includes var.labradorica, and ssp.interiorare recognized as distinct entities. The latter has a restricted distribution and can be easily distinguished morphologically owing to its glabrous calyces. The morphological variation between ssp.californicaand ssp.sibiricais continuous and some overlap occurs. The best diagnostic characters are two ratios: sheath length to flower head width and outer involucral bract length to flower head width. Geographic trends are obvious: a reduction in plant size with increasing latitude and an increase in frequency from west to east of hairy scapes and holotrichous calyces. The dimorphic and self-incompatible ssp.maritimais maintained because of its distinct breeding system (papillate stigma associated with finely reticulate pollen and smooth stigma associated with coarsely reticulate pollen). Subspeciesmaritimais only found in south Greenland and some specimens are morphologically similar to eastern monomorphic plants.Key words:Armeria maritima, North America, numerical taxonomy.

ISSN:0008-4026    

DOI:10.1139/b95-171

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

One hundred and fourteen isolates ofMacrophomina phaseolinafrom tissue of hosts in the Asteraceae, Euphorbiaceae, Fabaceae, and Poaceae, and from cultivated and noncultivated soils in Somalia (east Africa) and Arizona were tested for pathogenicity, ability to form pycnidia, and chlorate-utilization phenotype. Hyphal interactions of pairs of isolates from noncultivated soils in Somalia and Arizona were examined to address the possibility of genetic reproductive isolation of two geographically separated populations. Isolates from the Poaceae were less pathogenic and formed pycnidia less frequently compared with isolates from dicot host tissue. Chlorate-utilization phenotype was unrelated to host tissue source. However, isolates that infrequently or never produced pycnidia were more likely to have chlorate-sensitive phenotypes. Apparently successful hyphal fusions were observed for 64.3% of confrontations where one isolate was taken from Arizona and one was from Somalia, implying no barrier to genetic interchange at this initial level of interaction. WhileM.phaseolinais a heterogeneous species that cannot be partitioned into distinct subspecific groups based upon function, it appears that isolates colonizing the Poaceae are more restricted in pathogenicity than the general population.Key words: chlorate utilization, geographic isolation, host specialization, hyphal interactions,Macrophomina phaseolina.

ISSN:0008-4026    

DOI:10.1139/b95-172

出版商:NRC Research Press    

年代:1995

数据来源: NRC