摘要:

It is postulated that the changes in growth and metabolic activity that characterize many features of plant development are produced by the interaction between the hydraulic conductivity of the tissues and the influence of environmental factors, transpiration and osmotic gradients on the uptake, distribution, or loss of water. Mechanisms based on this concept are proposed for six aspects of development. These are (i) seed germination and stem elongation (water uptake), (ii) apical dominance and tropisms (water distribution), and (iii) leaf senescence and abscission (water loss). The postulated mechanisms are based on the hypothesis that water is the factor that normally limits the rate of growth and metabolic activity in the intact plant. The validity of the concept is supported by the unique capacity of water to perform three basic functions. These functions are (i) to mediate environmental effects on growth and metabolism, (ii) to correlate the growth of different parts of the plant, and (iii) to integrate growth and metabolic activity at the cellular level. It is also suggested that the responses induced by the application to plants of certain growth-regulating substances can be mainly attributed to the capacity of these substances to promote the uptake of water.

ISSN:0008-4026    

DOI:10.1139/b87-181

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Conidial and dry weight production ofVerticillium dahliaevaried greatly depending on the amino acid used as the nitrogen source in Czapek's–Dox medium. Variable fungal growth was also noted when mixtures of amino acids were used and growth was dependent on the type and concentration of each amino acid in the mixture. Similar variation was obtained when sugar maple (Acer saccharum) sap was amended with individual amino acids. These results are examined in relation to the reported variation in the amino acid content of host xylem sap and in relation to verticillium wilt development.

ISSN:0008-4026    

DOI:10.1139/b87-182

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The effect of growth temperature on the temperature responses of photosynthesis and on growth as estimated from plastochron measurements ofL.esculentum, a high-altitude ecotype ofL.hirsutum, and their hybrid was studied. The two species and their hybrid displayed similar temperature responses of photosynthesis when they were grown under a thermo-period of 25:18 °C. However, when the growth temperature was decreased to 12:5 °C, onlyL.hirsutumand the hybrid showed the ability to acclimate by increasing their photosynthetic rates at low temperatures. Growth exhibited a similar response to a shift to the low-temperature regime since the growth rate ofL.esculentumwas reduced to a greater extent than that ofL.hirsutum. Moreover,L.hirsutumresumed growth at a faster rate after a short period of time, whereasL.esculentumdid not. These results show that there are parallel differences in the capacity of photosynthesis and growth to acclimate to low temperatures betweenL.esculentumand the high-altitudeL.hirsutum.

ISSN:0008-4026    

DOI:10.1139/b87-183

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Morphogenesis following cell division inMicrasterias rotatais by outgrowth and repeated branching of a series of semicell lobes. Though successive branching events are qualitatively similar, they display changes in time and space scales, and these can be quantitated with the aid of autoradiographic patterns of labelled wall precursors that appear late in morphogenesis but which seem to represent its history. This enables us to consider branching as the conversion of a single centre of growth activity into two and to attempt to locate these centres precisely, in terms of both position and time of establishment. Temporal and spatial scales both decrease, by 75%, through a sequence of five branching events, in linear functional relationship to each other. This correlation points toward kinetic control of morphogenesis, i.e., the involvement of something like a reaction–diffusion mechanism. We analyse this possibility in terms of available reaction–diffusion theory to show how, after various simplifying assumptions, and if the time and space scales of branch formation are known, an effective diffusivity,, for the patterning mechanism can be estimated. ForM.rotatawe obtain orders of magnitude:, with an upper limit on the diffusivity of the faster diffusing of the two morphogenetic substances in the mechanism of ca. 1 × 10−7 cm2/s. These values implicate the cell membrane as the most probable site of pattern formation.

ISSN:0008-4026    

DOI:10.1139/b87-184

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

WinterellaO. Kuntze is proposed as the correct generic name for the fungi previously assigned toCryptosporaTul. & C. Tul. andOphiovalsaPetr. Eleven species are accepted in the genus, includingWinterella confusasp.nov.,W. wehmeyerianasp.nov.,W. albofusca(Cooke & Ell.) comb.nov.,W. alnicola(Höhn.) comb.nov.,W. aurantiaca(Wehm.) comb.nov.,W. aurantiacasubsp.valsoides(Rehm) comb.nov. Two new genera are proposed,Mycocryptospora(typeM.anthostomoides(Rehm) comb.nov.) andServazziella(typeS.longispora(Servazzi) comb.nov.). Forty-nine other fungi with names in the genusCryptosporaare discussed and, when possible, a disposition is suggested.

ISSN:0008-4026    

DOI:10.1139/b87-185

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Cytochemical and ultrastructural analysis of cell wall characteristics was performed in the dermal system of the grape berry (Vitis viniferaL. cv. Pinot noir), using a test for polysaccharides (periodic acid – thiosemicarbazide – silver proteinate, associated with dimethylsulfoxide extraction). Samples were examined at successive stages of fruit development. The main events of the first growth phase, i.e., thickening of hypodermal cell walls and their tangential extension, continued during the second growth phase. At all the stages of grape development, tangentially expanding walls were typical of actively growing plant cell walls, with an ordered texture, new layer deposition, and progressive rotation of microfibrillar subunits (bow-shaped patterns). At maturity, hydration, swelling of the walls, and an increase in the amount of soluble pectic substances were noticed. No redifferentiation of the cell walls occurred. The cuticle, already differentiated into two layers at the first growth phase, was clearly lamellar during the second. At maturity a number of layers, distinguishable by their cytochemical reactivity, were detected. Cuticle thickness increased during "véraison" and was maintained throughout the second growth phase. A considerable increase in the content of epicuticular waxes was noticed during ripening.

ISSN:0008-4026    

DOI:10.1139/b87-186

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

From 20 provenances of field-collected actinorhizae ofMyrica gale, more than 3000 test tubes were inoculated with OsO4-treated nodules. Only 30Frankiastrains were isolated from 6 provenances. Most isolates showed an extremely slow growth in the various isolation media tested. For 12 strains whose growth was sufficient, theFrankianature of isolates was verified by morphological characterization and biochemical analysis, using gas chromatography for the presence of 2-O-methyl-D-mannose. All 12 strains showed infectivity onM.galeandAlnus glutinosa. Five of those strains were ineffective onA.glutinosabut effective onElaeagnus angustifoliaandHippophaë rhamnoides.

ISSN:0008-4026    

DOI:10.1139/b87-187

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The effects of defoliation on biomass distribution were studied in plants ofHolcus lanatusL.,Lolium perenneL., andTrifolium repensL. collected from three different-aged pastures. Individual plants were cloned and ramets from each clone were subjected to clipped and unclipped treatments over a period of 1 year. In the unclipped treatment for each species, plants from the three pastures showed no differences in the extent of clonal growth (i.e., tiller or stolon production). In the clipped treatment, however, plants from the oldest pasture displayed significantly more extensive clonal growth than plants from the younger pastures. With increasing pasture age, there was a significant trend of increasing compensatory clonal growth in response to defoliation for all three species. This may be interpreted as a consequence of selection pressure from grazing. However, the data do not suggest that the grass–grazer relationship is a mutualism. Alternative interpretations are considered.

ISSN:0008-4026    

DOI:10.1139/b87-188

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Vegetation and environmental variables were examined in some coulees of the Oldman River near Lethbridge, Alta. Principal components analysis of environmental variables indicated that solar energy, aspect, soil Mg2+,, and moisture were related to the first axis of variation. Slope position, soil, moisture, K+,, and amount of bare ground were related to a second axis of variation. There was a large range in species diversity among plots; most diverse plots were on north-facing slopes. Direct ordination of vegetation data indicated that slope position and aspect were most important in describing distribution of species.Koeleria macrantha,Bouteloua gracilis,Stipa comata, andArtemisia frigidawere found on most coulee positions.Hymenoxys richardsonii,Machaeranthera grindeloides,Astragalus spatulatus, andEriogonum flavumwere mostly restricted to summit and upper slope positions.Anemone patens,Geum triflorum,Thermopsis rhombifolia, and others were most abundant on north- and east-facing slopes. Fewer species (e.g., the C4Aristida longisetaand the cactusCoryphantha vivipara) were mostly confined to south-facing positions.

ISSN:0008-4026    

DOI:10.1139/b87-189

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The barley –Ustilago hordei(Pers.) Lagerh. system was examined in selection experiments. Three populations were formed with teliospores originating from 15 different dikaryons (5 dikaryons per population). The teliospores were heterozygous for a gene governing virulence to the barley cultivar Trebi. Each population was subdivided such that one subpopulation was selected on 'Trebi' and the other was simultaneously selected on 'Odessa', partially resistant and susceptible cultivars, respectively. Changes in the virulence allele frequency were monitored during each generation of selection for each population. There were no major changes in percentage of smutted plants that could be attributed to the cultivar on which selection took place. Increases of the virulent phenotype were observed for all populations regardless of cultivar. Whether these changes were the result of changes of allele frequency or other factors is not known.

ISSN:0008-4026    

DOI:10.1139/b87-190

出版商:NRC Research Press    

年代:1987

数据来源: NRC