摘要:

Downy mildew disease of the cultivated peaPisum sativumL. caused by the fungusPeronospora pisiSydow was studied in mature leaves and young shoots of the host plant. Particularly in systemic infections of young shoot tissue, a common occurrence was an extremely electron-opaque membrane-bound, hemispherical deposit extending through the host cell wall into the host cytoplasm. This material which abutted directly onto the intercellular hyphal wall was termed the penetration matrix. Its formation was apparently the result of a specific interaction between the host and obligate fungal parasite. Similar apparently solid or gellike material constituted the matrix surrounding the digitlike intracellular haustorium. This membrane-bound extrahaustorial matrix was present through the penetrated host cell wall and formed a relatively thick layer around haustoria in young shoot tissue, but was much thinner distally around haustoria in mature leaf mesophyll cells. An unusual, regularly arranged, tubular network of ribosome-free endoplasmic reticulum was occasionally found in the host cytoplasm in systemically infected shoot tissue adjacent to haustoria.

ISSN:0008-4026    

DOI:10.1139/b77-323

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

not available

ISSN:0008-4026    

DOI:10.1139/b77-324

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Chlordane is an organochlorine soil insecticide whose effects upon aquatic ecosystems, and particularly on algae, are little known. Experimental results indicate that chlordane concentrations ranging from 0.1 to 100 μg/ℓ significantly stimulate cell division ofScenedesmus quadricauda, a common planktonic green alga. Chlordane in concentrations from 0.1 to 50 μg/ℓ is also stimulatory to the growth ofChlamydomonassp., isolated from soil. However, 100 μg/ℓ was inhibitory to cell division in this species.Significant stimulatory effects on the respiration rates of these two species were observed at all concentrations within 3 to 4 h of chlordane addition. Stimulation of respiration increased with increasing chlordane concentration. Similar stimulatory effects on respiration were produced using 2,4-dinitrophenol (DNP), a known uncoupling agent of oxidative phosphorylation. Long-term inhibition of photosynthetic response ofScenedesmus quadricaudatreated with the higher chlordane concentrations was observed over the course of the experiment even though a significant increase in cell numbers over the control was noted. A highly significant chlordane–light interaction was observed on photosynthesis of bothS. quadricaudaandChlamydomo

ISSN:0008-4026    

DOI:10.1139/b77-325

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The development of substomatal sacs and the capacity of the underlying ion-adsorbent sites to accumulate potassium is examined in relation to the ontogeny of the stomatal complex and mature guard cells of the fern,Polypodium vulgare. It is suggested that while the substomatal structures are formed at an early stage of stomatal development, their functional capacity may not be fully realised until the guard cell complex is fully matured.

ISSN:0008-4026    

DOI:10.1139/b77-326

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The distribution and general ecology of 263 bryophyte taxa are presented for an extensive area of coniferous forest, open fens, and alpine terrain along the Mackenzie River in the District of Mackenzie and the Peel River, a major tributary which extends into the Yukon. The continuous or discontinuous permafrost which underlies the area plays a major role in determining the vegetational communities that are present. Fire and disturbance by man initiate succession. Thirty-nine liverworts, 20 peat mosses, and 204 true mosses are reported. There are 43 new reports for the District of Mackenzie and 16 for the Yukon.Cynodontium glaucescensis new to North America.Brachythecium glaciale, B. mildeanum, andB. trachypodiumare confirmed for North America. Of the taxa 94.7% are found in Europe and Asia as well as North America, 4.2% are known only from Asia and North America, whereas only 1.1% are restricted to North America. High mountains in the western part of the area, generally nonglaciated during the Wisconsinan, support a flora that contains many Arctic and Arctic–Alpine taxa.

ISSN:0008-4026    

DOI:10.1139/b77-327

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Circaea×intermediaEhrh. in North America is an interspecific hybrid betweenC. alpinaL. andC. lutetianaL. subsp.canadensisAschers. & Magnus. In spite of the morphological differences that exist between the European and North American subspecies ofC. lutetiana, hybrids from both continents are morphologically identical. Documentation of the intermediacy of the hybrid taxon is presented based on the evaluation of the means of 22 characters of specimens from an Ontario locality at which all three taxa are found.Diploid chromosome counts of 2n = 22 are reported for Ontario populations of the hybrid and parental species. The presence of irregular, somatic chromosome numbers are also reported for all three taxa.Distribution maps for all three taxa in eastern North America are included. In the case ofC. lutetianasubsp.canadensis, the northern range is sharply delimited by the Precambrian–Paleozoic bedrock boundary.A table of character comparisons and a key to the three taxa summarizes the salient characteristics of the hybrid and the parental species in eastern North America.

ISSN:0008-4026    

DOI:10.1139/b77-328

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Light microscope observations were made of the developmental morphology, life cycle, and host range of a strain ofHaliphthoros milfordensisVishniac isolated from the pink shrimp,Penaeus duorarum. Zoospores of the isolate, by virtue of their variation in shape and subapically attached flagella, are not as described previously for this genus. However, they are biflagellate and therefore characteristically oomycetous. Encystment of spores begins with flagellar retraction and rounding-up and terminates with the formation of an external, spined cyst wall. Germination is monopolar, producing germ tubes of various dimensions which fan out into hyphae. Vegetative growth is accompanied by multibranching at right angles and fragmentation. Sporogenesis is holocarpic but unusual in that thallus conversion into spores occurs in delimited segments non-simultaneously and in that spore cleavage is sequential, beginning in the sporangium and ending in the discharge tube. Infectivity tests indicate thatH. milfordensisis a facultative parasite occurring on several crustacean hosts: however, the site of infection varies according to host structure.

ISSN:0008-4026    

DOI:10.1139/b77-329

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Constricting ring traps ofDactylaria brochopagaDrechs. were found to be effective trapping agents. Nematodes were held by inflation of the ring cells, inflation resulting from changes in the wall of the luminal face of such cells. The wall structure of the ring cells was found to be more complex than has been previously reported for similar fungi. Membrane-bound, osmiophilic, dense-staining, lysosome-like inclusions were found associated with the trapping surface and appear to play a role in both the trapping and the subsequent penetration process. The ultrastructure of (1) the trapping apparatus before and after its inflation and (2) the nematodes and hyphae during the infection process was studied and is reported herein.

ISSN:0008-4026    

DOI:10.1139/b77-330

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The host–predator relationship of the myceliophagous nematodeAphelenchus avenueBastian and the predaceous hyphomyceteDactylaria Candida(Nees) Sacc. was investigated under laboratory conditions, using phase-contrast microscopy of whole-mount preparations and thin resin (Spurr) sections. Adhesive trapping knobs were profusely produced byD. Candidaand these proved efficient nematode-trapping agents. Nonconstricting rings were rare and never seen to be operative.Dactylaria Candidawas found to be capable of parasitizing nematode eggs.

ISSN:0008-4026    

DOI:10.1139/b77-331

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The host–predator relationship of the myceliophagous nematodeAphelenchus avenaeBastian and the predaceous hyphomyceteDactylaria Candida(Nees) Sacc. was investigated using scanning electron microscopy of whole-mount preparations and transmission electron microscopy of ultrathin resin (Spurr) sections. Trapping knobs and knobs with associated hyphae were found to be effective nematode-trapping agents. The ultrastructure of the trapping apparatus and of the nematodes and hyphae during the infection process is reported herein, as is the phenomenon of postinfection 'breakout.' Nonconstricting rings were not observed during this study.

ISSN:0008-4026    

DOI:10.1139/b77-332

出版商:NRC Research Press    

年代:1977

数据来源: NRC