摘要:

Members of the Chenopodiaceae and Cruciferae were reported to be nonmycorrhizal by early investigators; more recently, some species in these families have been reported to have low or in some cases high levels of vesicular–arbuscular (VA) mycorrhizal infection. In our experiments, a sparse vesicular (chlamydospore) infection byGlomus fasciculatuswas found in four species of Chenopodiaceae and two species of Cruciferae but only when grown in the presence of a mycorrhizal companion plant, citrus or onion. No arbuscules were observed in infected roots.Chenopodium albumhad the highest incidence of infection (5%). Infection was restricted to older tissue and penetration of the vascular cylinder was common, which is atypical of VA mycorrhizae. As hyphae from mycorrhizal companion plants grew through the soil, they encountered older roots of the test plants which probably offered little or no resistance to infection. In documenting the occurrence of VA mycorrhizae in any species, it is important to observe whether the plant is growing by itself or if there are mycorrhizal plants closely associated with it. Also, care should be taken not to confuse common root parasites for the fungal structures of VA mycorrhiza.

ISSN:0008-4026    

DOI:10.1139/b78-336

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Didymella proximellais reclescribed and illustrated from collections onCarex californienfrom Mary's Peak. Oregon. The Oregon specimens match the type ofD. proximellafrom Finland. Ascostromata ofD. proximellaand pyenidia of aStagonosporaspecies were found on overwinteredC. califomicain Oregon; ascospores yielded the sameStagonosporaon agar. This species ofStagonosporcis morphologically distinct fromStagonospora strictaand the presence of ascostromata ofD. proximellawith pyenidia ofS. strictaon the same lesions in the type ofS. strictais fortuitous.

ISSN:0008-4026    

DOI:10.1139/b78-337

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Changes in rates of respiration and net photosynthesis inStereocaulon paschale(L.) Hoffm. in relation to temperature, moisture, and light have been documented for a woodland population collected in the Abitau–Dunvegan Lake area of the Northwest Territories. The temperature optimum for net photosynthesis is about 20–30 °C and not 0 °C as has been previously reported in the literature. Maximal rates of net photosynthesis are only developed at low levels (100–150% water content by weight) of thallus saturation, suggesting a good degree of adaptation to the xeric conditions normally found in spruce–lichen woodland. Similarly the relatively high light requirement of 1000 μE ∙ m−2 ∙ s−1correlates well with the open nature of lichen woodland and especially with the disappearance ofStereocaulon paschalein old woodland with the closure of the canopy.The sensitivity ofStereocaulon paschale, when dry, to thermal stress is examined in detail and even the moderate thallus temperature of 35 °C is shown to be highly stressful to this species. Surface temperatures in the low arctic are often above 35 °C and over recently burnt surfaces, temperatures above 45 °C occur on a regular basis. Thus the delayed entry ofStereocaulon paschaleinto the successional sequence reflects its extreme sensitivity to thermal stress. With the gradual accumulation of an organic layer and an enhanced retention of soil moisture over the initial 60 years of succession there is a significant reduction in both the sensible heat flux and the surface temperatures. At the same time, tree growth leads to a sharp decrease in direct radiation, and the combination of these two developments results in a much cooler surface and one which can be colonized byStereocaulon.It is suggested that thermal stress tolerance of lichens in an air-dry state, to either high or low temperatures may be centrally important to their overall ecology. Furthermore the net photosynthetic response pattern to temperature, moisture, light, and time of year may, in fact, play a subordinate role in the ecology of a lic

ISSN:0008-4026    

DOI:10.1139/b78-338

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Young tomato plants were treated with gibberellic acid (GA3) at a stage before floral initiation. In the first truss produced after the treatment, the fresh weight and size of the fruit was lower than the controls but was significantly higher in trusses 2 to 4. Also, whereas in controls the fresh weight and size of tomato fruits steadily declined from truss 1 to truss 4, in GA3-treated plants there was a progressive increase in the fresh weight and size of the fruit. The number of locules per fruit of GA3-treated plants was also greater than the controls but not the number of seeds per fruit. Regression analyses show that both the locule number and seed number have a significant correlation with the fresh weight of the fruit and that these relationships are independent of each other.

ISSN:0008-4026    

DOI:10.1139/b78-339

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Guard cells inOphioglossum petiolatumleaves are initiated by a single division of a stomatal initial with no subsidiary cells being formed. The stomatal initials have few vacuoles, plastids with little starch, and a large nucleus with much heterochromatin and prominent nucleoli. Young guard cells are similar cytologically to stomatal initials; their common cell walls are thin and traversed by plasmodesmata. Plasmodesmata are also present within guard cell and adjacent epidermal cell walls. With increasing age, guard cells develop a lenticular thickening in the median portion of the common cell walls, larger vacuoles, and plastids with several starch grains. Numerous microtubules are present near the thickening wall which also has an electron-translucent region between the cell wall and the plasmalemma. Many dictyosomes and mitochondria are present in the cytoplasm. Older guard cells become more vacuolated, with some of the vacuoles containing fibrillar or dense deposits. Plastids become very large as a result of storing several large starch grains. In the thickened portion of the cell walls, the middle lamella and some of the adjacent cell wall appear to be degraded during stomatal pore formation. Mature guard cells are highly vacuolated and have very thick electron-dense cell walls without plasmodesmata. Fluorescence microscopy following aniline blue staining shows that aniline blue positive materials are present around and within the thickened portion of the cell walls, at the junction of guard cells with epidermal cells, and as distinct spots in guard cell and epidermal cell walls during the early stages of ontogeny. Mature guard cells, however, lack the distinct fluorescent spots, which are interpreted as plasmodesmata, in their walls.

ISSN:0008-4026    

DOI:10.1139/b78-340

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

An examination of pollen morphology and ultrastructure of Eremolepidaceae (Antidaphne, Ixidium, Eremolepis, Eubrachion) andLepidocerasby light and scanning and transmission electron microscopy reveals a close relationship among the taxa. Pollen of Eremolepidaceae is typically echinate, tricolporate, and oblate-spheroidal.Eubrachionis unique within the family, exhibiting shallowly reticulate pollen. Ultrastructurally, all Eremolepidaceae exhibit a similar exine structure. The sculptural ektexinous elements (spines or 'muri') are never contiguous with the basal ektexine but rest on a thin granular zone. Pollen characters ofLepidocerasare particularly close to those ofIxidiumandEremolepis. The porate (por(or)ate) aperture type, completely spherical shape, and reduced granular ektexine ofLepidoceraspollen indicate an advanced position within the complex. The relationship ofTupeiato Eremolepidaceae is more obscure as pollen of the genus exhibits both eremolepidaceous (echinate sculpturing, shape in polar and equatorial views) as well as loranthaceous characters (simple apertures, ektexine organization). Palynologically Eremolepidaceae and related genera show no particular close relationship to Olacaceae or Santalaceae. Though Eremolepidaceaeet al. do share a number of pollen features with Viscaceae (echinate sculpturing, compound apertures, exine organization) the strong nonpalynological differences between the two families suggest that these pollen features may have arisen independently.

ISSN:0008-4026    

DOI:10.1139/b78-341

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Germination of basidiospores inFomes fomentarius(Fries) Kickx is bipolar with germ tubes emerging at both ends. Ungerminated spores are smooth with a thick cell wall consisting of two layers: an outer thin, electron-dense layer and an inner thick, electron-light layer. During the early stage of germination, two additional cell wall layers are formed: a very thin, electron-dense layer and a relatively thick, electron-light layer. Germ tube walls originate from these newly formed, inner layers. Ungerminated spores are uninucleate and contain numerous lipid bodies, ribosomes, and cisternae of endoplasmic reticulum. Germinated spores have distinct mitochondria and an invaginated plasma membrane and are usually devoid of endoplasmic reticulum.

ISSN:0008-4026    

DOI:10.1139/b78-342

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Cycloheximide treatment (3.6 × 10−6 M) inhibits the incorporation of [2-14C]acetate into protein, asparagine, and the organic acids and sugars fraction. At the same time, it enhances the release of14CO2and the incorporation of carbon into glutamine and the neutral and basic amino acid fraction. Eight structural analogues of cycloheximide were tested for their effects on protein, asparagine, and glutamine formation in corn root tips. Two analogues, cycloheximide acetate and streptovitacin A (at a concentration of 1.8 × 10−5 M), acted in a manner similar to cycloheximide. Their effect was to inhibit protein and asparagine synthesis and to enhance glutamine formation. Six other analogues (1.8 × 10−5 M) had no marked effect on these fractions. The results of this investigation indicate that the structural analogues which inhibit asparagine formation in corn root tips also inhibit protein synthesis. The results suggest that the hydroxyl group of the hydroxyethylglutarimide portion of the cycloheximide molecule and the ketone-carbonyl group of the cyclohexanone ring are important for their action on protein synthesis in corn root tips.

ISSN:0008-4026    

DOI:10.1139/b78-343

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Fixation with a mixture of tannic acid and paraformaldehyde–glutaraldehyde resulted in an increased electron density of the membrane structure of tubular bodies that were associated with mycoplasma organisms (MLO) inVinca roseaplants infected with the Alberta isolate of the aster yellows agent. The tubular bodies, 25.5 ± 4.3 nm in diameter, were bounded with membranes in contrast with the hollow cylinders of 12.3 ± 3.0 nm in conventional fixation. In the study of physical relationships, the tubular bodies were often connected with MLO by a common unit membrane. Some subtubules were formed from a main tubular body.

ISSN:0008-4026    

DOI:10.1139/b78-344

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

It is proposed that the chloroplasts ofEuglenahave arisen from the progressive reduction of endosymbiotic green algae. The theory is supported by the presence of a third membrane around the chloroplasts ofEuglenawhich is not endoplasmic reticulum (ER) in origin and may be derived from the plasmalemma of the original symbiont. In addition,Euglenais the only organism in which chloroplast loss can be induced experimentally. Dinoflagellate chloroplasts are also surrounded by three membranes, and it is proposed that they too evolved from symbiotic eucaryotic algae.

ISSN:0008-4026    

DOI:10.1139/b78-345

出版商:NRC Research Press    

年代:1978

数据来源: NRC