摘要:

This study documents thein vitrogrowth of N2-fixing root nodules from the dicotyledonous shrubCeanothus integerrimus(Rhamnaceae). Root nodule lobes were removed from cultivated plants, surface sterilized, and cultured on agar media containing varied amounts of nitrogen (N). Uninfected cells inside the cultured nodules divide and form a callus which is visible after 7 days of growth. Cells infected by the N2-fixing actinomycete do not divide, but rather degenerate. Host cell cytoplasm disappears and organelles and the plasma membrane are no longer seen under the electron microscope. Endophyte structure also deteriorates. Nucleoid areas within the terminal vesicles become diffuse. Cross walls separating vesicles from the hyphae disappear and cytoplasm of the hyphae withdraws from the actinomycete wall.Ceanothusnodules readily form callus in tissue culture. Callus proliferates from uninfected cortical parenchyma outside the infection zone. The callus is free of living endophyte and is incapable of fixing N2as measured by acetylene reduction. Nodule tissue growthin vitrois more vigorous on media with high N than on N-deficient media.

ISSN:0008-4026    

DOI:10.1139/b80-138

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Developmental and ultrastructural aspects of conidiomata (pycnidia) inChaetomella acutisetavar.acutisetawere examined in pure culture and on sterile oak leaves. The earliest recognized sign of pycnidial formation in this fungus is the aggregation of hyphae at the base of an erect seta. Subsequently, the hyphae adjacent to the seta become intermingled and then orient themselves parallel to one another as they rise up from the surface of the substrate. Additional setae form about the perimeter of the young pycnidium. Ontogenetic features of the cavity of conidiomata were examined by cryo-sectioning. As the pycnidium enlarges, the internal hyphae become more loosely packed and then differentiate into conidiophores bearing phialides.

ISSN:0008-4026    

DOI:10.1139/b80-139

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The four experiments described permit the following methodological conclusions to be derived: (1) The time required for flowering and the number of leaves preceding the first flower on the principal axis are both necessary to compare the effect of treatments on progress towards flowering. One can conclude that a factor is favorable or unfavorable, only if it entails for both measurements a modification in the same direction. (2) Lateral axes are equally usable even in a case in which the treatment involves a preinduction phase and in which the principal axis alone does not permit a conclusion. In some cases the effect of a factor may be more evident on the lateral axes than on the principal axis.

ISSN:0008-4026    

DOI:10.1139/b80-140

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

To understand the adaptation of the life cycle of ferns to cold regions, the freezing resistance of gametophytes and sporophytes of the temperate fern,Polystichum retroso-paleaceum, was evaluated in Sapporo. The mature sporophytes were hardy to −15 °C, but not to −20 °C. However, marginal cells located in the wing part of the gametophytes remained alive after freezing to −70 °C, and even to −196 °C. It was also observed that these surviving cells, after freezing to very low temperatures, resumed growth and grew into new gametophytes. Present evidence provides a demonstration of the adaptability to cold climates of the gametophytic generation of ferns.

ISSN:0008-4026    

DOI:10.1139/b80-141

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The interaction between the phytotoxicity of certain phenolic compounds and deprivation of certain nutrients was investigated by means of a factorial experiment. Two concentrations ofp-coumaric acid and two of vanillic acid were added to nutrient solutions containing various quantities of nitrogen and phosphorus, and these solutions were tested on barley plants in sand culture. Phenolic toxicity appears to depend intimately on nutrient concentrations; the phenolic acids were uniformly and significantly inhibitory only at low nutrient concentrations. Allelopathy with phenolics as chemical inhibitors seems most likely to occur in nutrient-poor soils.

ISSN:0008-4026    

DOI:10.1139/b80-142

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Scytalidium uredinicolais a destructive hyperparasite of western gall rust,Endocronartium harknessii, that reduces the inoculum potential of the rust. It disintegrates spores and the basal cell region of the active rust sori and produces abundant arthroconidia among the rust spores to give the infected sori a yellowish-green to whitish-gray appearance, depending on the stage of infection. Hyphae ofS. uredinicolaare able to penetrate the wood tissue of the galls and destroy rust hyphae to a depth of 300 μm below the sori. When the parasite hyphae accumulate in the wood tissue, rust hyphae below the invaded area also appear to be degraded. On water agar, hyphae ofS. uredinicoladisintegrate rust spores within 48–72 h, without penetration. The use ofS. uredinicolafor biological control of pine stem rusts is considered promising.

ISSN:0008-4026    

DOI:10.1139/b80-143

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Thein vivoactivity of xanthine dehydrogenase measured in cotyledons ofPharbitis nildepended on the environmental conditions to which plants had been subjected before measurement. The lowest value was obtained in plants placed under light (110 W m−2) in 21% O2and 0.03% CO2, and represents approximately one fourth of the activity of the dark control. The activity could be increased in illuminated plants either when CO2was removed from the atmosphere or when DCMU (dichlorophenyldimethylurea) was given to the cotyledons. The effect of DCMU on the level ofin vivoactivity of xanthine dehydrogenase was removed completely by a supply of sucrose to the cotyledons. Furthermore, it was shown that a reduction of the O2concentration in CO2-free air surrounding the plants enhanced the activity of xanthine dehydrogenase in both illuminated and darkened plants.The results are discussed in relation to the mechanism by which photosynthetic activity could regulate the level of the activity of xanthine dehydrogenase.

ISSN:0008-4026    

DOI:10.1139/b80-144

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Seasonal changes in the densities of epiphytic and epipelic algae were determined during 1975 and 1976 at two sites on the north shore of Great Slave Lake. The epiphyton waxed rapidly in May and reached maximum densities of 5–6 × 108 μm3/cm2in June. Although densities remained high during the summer, they fell rapidly in October, followed by a secondary peak in November. The main species wereTabellaria flocculosa, Achnanthes minutissima, Achnanthes linearis, Gomphonema intricatum, andLyngbya diguetii. The epipelon, consisting largely ofNitzschia palea, Nitzschia dissipata, Fragilaria construens, andOscillatoriaspp., also showed spring and fall peaks in densities, with maximum populations of 4.2 × 108 μm3/cm2being recorded in June and July. The growing season for both communities was limited by the formation of ice in the fall, whereas the maximum standing crop of the flora was at least partially restricted by low nutrient levels (total phosphorus, 0.008 mg/L; total alkalinity, 30 mg/L).Seasonal changes in the density of epipelon were monitored during 1977 and 1978 at a third site on the north shore of the lake, where total phosphorus and total alkalinity ranged up to 0.010 and 94 mg/L, respectively. Prevalent taxa includedCymatopleura elliptica, Epithemia turgida, Rhopalodia gibba, Cymbellaspp., andNostocspp. The growth cycles of the flora were again characterized by spring and fall peaks in numbers. Algal densities were, however, high (up to 2.3 × 109 μm3/cm2), possibly a reflection of nutrient availability.Samples of epiphyton and epipelon were taken at an additional seven sites in the east arm of the lake during June and July 1975. The main epiphytic species wereCocconeis placentula, Achnanthes minutissima, andTabellaria flocculosa, while prevalent epipelic taxa includedNavicula graciloides, Fragilaria vaucheriae, Tabellaria flocculosa, andAchnanthes minutissima. Densities were less than those recorded from the three sites on the north shore, again possibly a reflection of nutrient availability.

ISSN:0008-4026    

DOI:10.1139/b80-145

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The primary productivities of a natural lake, a new reservoir, and an established reservoir were investigated in western Labrador over two seasons. Productivity of the new reservoir was about twice those of the other two sites. Possible causes for this increased productivity were examined. It was found that differences in productivity were due to differences in standing stocks of plankters only, and not due to differing photosynthetic efficiencies, better light, or a combination of these factors. Since changes in biomass may be predicted from changes in phosphorus concentration, these findings support the hypothesis that the increased productivity in new impoundments may be explained by the increase in phosphorus concentration.

ISSN:0008-4026    

DOI:10.1139/b80-146

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Nonrandom variation in gas exchange of the three arctic lichensCladonia rangiferina(L.) Wigg.,Cladonia stellaris(Opiz) Brodo, andParmelia separataTh. Fr. is documented through a combination of field and laboratory studies. The highest rates of both photosynthesis and respiration occur in the youngest, actively growing sections of the thalli and both parameters decrease progressively into the older sections. For the twoCladoniaspecies gross photosynthesis is shown to vary directly as a function of chlorophyllaandbconcentration as found in a vertical profile through the lichen mat.

ISSN:0008-4026    

DOI:10.1139/b80-147

出版商:NRC Research Press    

年代:1980

数据来源: NRC