摘要:

The histological events leading to shoot formation inNicotiana glaucaand in the nontumorousNicotiana glauca×Nicotiana langsdorffiihybrid have been studied. Organized development begins from a single vacuolated parenchyma cell which divides and precociously differentiates tracheidal cells, forming a growth center with nodular structures with xylem in the center and phloem outside. The vascular tissue is precociously separated from the surrounding callus by a layer of cells which are shown to be endodermal by position and by histochemical reactions. Further growth leads to the formation of a mound of meristematic tissue which later forms shoot apical meristems. The sequences of events are discussed in relation to other known systems of regeneration in calluses.The system described could be suitable for evaluating the effects of various physical and chemical agents on the different steps of differentiation.

ISSN:0008-4026    

DOI:10.1139/b81-259

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The peatlands of eastern Newfoundland are classified into six morphological types: domed bog, blanket bog, slope bog, basins bog, ribbed fen, and slope fen. The separation of types is based on peat depth, surface physiognomy and slope, underlying basin or slope morphology, botanical constituents, and degree of humification of the peat strata. Low elevation aerial oblique photographs and stratigraphical profiles of the six representative morphological peatland types are presented.The peatland vegetation is classified into eight associations and four pool communities; three alliances are also proposed and comparisons with syntaxonomical classifications of European peatlands are discussed. Phytosociological tables are presented for the dry bog vegetation, wet bog vegetation, and fen vegetation; a summary table showing differential species groups of each syntaxon is also presented. pH and total contents of nitrogen, calcium, and iron are determined for the major vegetation types.

ISSN:0008-4026    

DOI:10.1139/b81-260

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The relations between host and parasite in the haustoria ofThesium humifusumhave been studied by scanning electron microscopy combined with an energy dispersive system. The distribution of mineral elements in the connecting tissues binding the host and parasite has been determined. It has been shown that the concentrations of phosphorus and potassium were higher in the hyaline tissue and in the intertracheidal parenchyma; the concentration of silicon was higher in the tracheids of the lignified transfer bridge and the concentration of calcium was higher in the cortical parenchyma and secondary phloem of the host root.These results support the existence of an osmotic gradient in the haustorium and between the two partners in the direction of the parasite. This gradient together with the transpiration pull and the intense acid phosphatase activity in the tissues may explain the movement of water and mineral substances from host to parasite.

ISSN:0008-4026    

DOI:10.1139/b81-261

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Apple seedlings germinated and grown under greenhouse conditions were inoculated with endomycorrhizal roots originating from a nursery grownFraxinusprior to outplanting into unsterilized field soil. Uninoculated seedlings, in soil either unamended or amended with 100 kg/ha P as superphosphate, were controls. Shoot length, leaf surface, root volume, stem diameter, and dry mass of inoculated plants were all significantly greater than both fertilized and unfertilized controls. No significant difference could be observed in foliar mineral content but the level of N, P, Ca, Cu, and possibly K were higher in the roots of inoculated plants than in controls. Although shoot length of the phosphorus fertilized plants exceeded that of the unfertilized controls (p < 0.05), all the other growth parameters remained unchanged by the addition of P. Intracortical vesicles were absent or very uncommon in the roots of both fertilized and unfertilized control plants whereas they were very abundant in the roots of inoculated plants.It is concluded that inoculation of seedlings previous to field planting in unsterilized phosphorus-poor soil can lead to a significant growth stimulation in spite of the presence of a natural endomycorrhizal flora.

ISSN:0008-4026    

DOI:10.1139/b81-262

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

An ultrastructural study of the vegetative shoot apex ofHelianthus annuusL. cv. Peredovic has shown that in most respects the cytoplasmic components of the central zone cells were similar to those of the mitotically active peripheral zone cells. For example, the mitochondria, dictyosomes, endoplasmic reticulum, ribosomes, and microtubules were not different either in their structure or in distribution in the two types of cells. The only striking difference found was the presence of starch-containing plastids in the central zone, primarily in the two tunica layers in this region, and their absence from peripheral and immediately subjacent regions of the meristem. Starch-containing plastids were observed in the differentiating pith cells. Plasmodesmata were observed in the central zone and in walls between central and peripheral zone cells.

ISSN:0008-4026    

DOI:10.1139/b81-263

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Descriptions and illustrations are provided for 15 species ofDidymella:D.alectorolophi,D.applanata,D.astragalina,D.bryoniae,D.castillejae,D.delphinii,D.eupyrena,D.exigua,D.festucae,D.glacialis,D.hellebori,D.pedicularis,D.phacae,D.proximella,D.trifoliiand forDidymella(?)abieticola,Pseudomassaria corni,Lophiosphaera lophosporacomb. nov., andMycosphaerella prominula. A key to the species and a host index are also provided. Species ofDidymellaincluded in this study fall into two small but well-defined subgeneric groups and one large heterogeneous intermediate group.

ISSN:0008-4026    

DOI:10.1139/b81-264

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

The effect of shifting pH of the growth medium on cell cycle initiation by the yeastCandida utiliswas studied. The yeast was grown by the phased method of cultivation with nitrogen source (ammonium) in growth limiting concentrations and with a phasing period (imposed doubling time) of 6 h. The pH of the culture during the phased growth was maintained between 2.0 and 2.1. The rate of cell cycle initiation as determined by the rate of bud emergence was 24% per hour. If the pH of the culture was shifted to 6.0 at the beginning of the phasing period and maintained at that level for the rest of the phasing period the rate of bud emergence increased to 50% per hour. The increased rate of bud emergence was accompanied by a fast uptake of oxygen and the growth-limiting nutrient and by a reduction in the respiratory quotient. The results suggest that the pH shift accelerated cellular processes necessary for cell cycle initiation.

ISSN:0008-4026    

DOI:10.1139/b81-265

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Zoospore ultrastructure ofPolyphagus euglenaeNowakowski, a parasite of algae, was studied using transmission electron microscopy. The elongate zoospore contains a centrally located nucleus covered by a ribosomal aggregation. Membranes, continuous with the nuclear envelope, concentrically traverse the ribosomal aggregation and form a lateral membranous labyrinth. In the posterior end of the zoospore, a single prominent microbody–lipid globule complex (MLC) lies adjacent to the nucleus. Oval microbodies cover the anterior aspect of the lipid globule, and a fenestrated cisterna (the rumposome) covers the posterior aspect of the lipid globule. Several of the elongate and branched mitochondria that bind the ribosomal aggregation are near the microbodies, and these mitochondria are also part of the MLC. The flagellar apparatus includes a parallel oriented kinetosome and secondary centriole, as well as a rootlet that extends laterally between the kinetosome and the plasma membrane and passes over a portion of the rumposome. Regularly banded and homogeneous configurations of the rhizoplast are found. Cored vesicles and vesicles containing heterogeneous inclusions are scattered in the outer regions of the cell. In the diaminobenzidine cytochemical technique for the visualization of catalase, microbodies are lightly stained, and this staining is inhibited by aminotriazole. Inflated regions of the nuclear envelope and ribosomal aggregation cisternae also contain electron-dense reaction product. Because staining of endomembranes is inhibited by sodium azide but not by the inhibitor of catalase activity, aminotriazole, it is concluded that catalase, which may have low activity, is present only in microbodies. Because of the distinctive structure of the flagellar apparatus, ribosomal aggregation and cisternal system as well as the position of the MLC, zoospore ultrastructure ofP.euglenaeis clearly distinct from any other chytrid zoospore that has been studied.

ISSN:0008-4026    

DOI:10.1139/b81-266

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Thelephora terrestrisbasidiospores germinate slowly and sparsely on nutrient agar media if colonies of red yeast (Rhodotorula glutinis) or certain filamentous fungi are present together with the spores. Considerably faster germination at a higher percentage can be induced by seedling roots of pine and some other trees but not by roots of any herbs or grasses as yet tested. Germination is further improved if inhibitory compounds in the autoclaved agar medium are removed by means of activated charcoal. A consequence of these findings is thatT.terrestris, which forms basidiocarps in pot culture and is an efficient ectomycorrhiza former, can be studied in all phases of its complete life cycle in the laboratory.

ISSN:0008-4026    

DOI:10.1139/b81-267

出版商:NRC Research Press    

年代:1981

数据来源: NRC

摘要:

Submerged leaves inSalviniaarise as single cells from the shoot apex. Shortly after initiation the primordium appears as a conical group of cells with two areas of lateral expansion toward the base. These two lateral regions plus the abaxial surface between them are the sites of initial leaflet production in the primordium. Following the appearance of the first set of seven leaflets, an additional set of leaflets is initiated and they become apparent as the submerged leaf emerges from the terminal bud. The growth of the submerged leaf is protracted compared with the floating leaves of the same set. Compared with the precisely located abaxial meristems found inSalviniafloating leaves, no discrete, regularly positioned meristems occur in submerged leaves. Thus, developmentally these compound leaves have little in common with the floating leaves or with other highly divided leptosporangiate fern leaves. The development of the floating and submergedSalvinialeaves is discussed with respect to leaf development patterns of widespread distribution in higher plants.

ISSN:0008-4026    

DOI:10.1139/b81-268

出版商:NRC Research Press    

年代:1981

数据来源: NRC