摘要:

The net photosynthetic response matrix to four light levels combined with four temperatures and for a full range of thallus hydration has been defined for aCladonia–woodland population ofCladonia rangiferinain midsummer and early winter. Maximum rates of net photosynthesis are generated between 150 and 200% thallus water content by weight between 15 and 25 °C with low rates being generated at 5 and 35 °C. Light saturation occurs above 600 μE∙m−2∙s−1. There is no evidence of acclimation of photosynthetic optima to temperature but with the onset of early winter there is a marked decrease of respiration rate. An examination of the sensitivity ofCladonia rangiferinain an air-dry state to heat stress shows a rapid decline of net photosynthesis under 45 °C daytime stress. Although 35 °C initially reduces the level of net photosynthesis to some extent, over a 3-week experimental period no further decline is observed. It is suggested that this population ofCladonia rangiferina, which is markedly restriced to a position under the shade ofLedumshrubs, is protected there from the otherwise excessive heat load which occurs on the openCladonia stellarissurface and which typically reaches 40 °C under full radiation conditions in sum

ISSN:0008-4026    

DOI:10.1139/b80-214

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The general organisation and functioning of the secretory cells of the glandular hairs ofHygrophila difformisshow some analogies with previously studied glandular systems of the same type; they differ from the latter, however, in the complexity of organisation of the reticulum – plastid complex.In the undifferentiated cell the plastids have a simple rounded, slightly elongated form; they display no special relationship with the endoplasmic reticulum which, at this stage, is represented by irregularly enlarged cisternae containing a dense substance of fibrous appearance.During the secretory phase, on the contrary, the ultrastructures of the plastids and of the endoplasmic reticulum undergo considerable changes; the latter appears in the form of small tubes arranged parallel to each other and in close contact with the plastids. The plastids themselves take on shapes which, until now, have never been observed in this type of cell and which can only be shown clearly by a three-dimensional reconstruction. This technique, which involves making a series of thin sections, has been applied to secretory plastids for the first time. It gives a faithful picture of their original morphology and the various modes of association possible between the plastids of a given reticulum – plastid complex.

ISSN:0008-4026    

DOI:10.1139/b80-215

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The nucellar epidermis ofOrnithogalum caudatumis modified in its micropylar region to form a nucellar cap. The cells become palisadelike with lignified walls and dense, RNA-rich cytoplasm and a large distal vacuole. High vesicular activity is associated with the greatly thickened proximal walls. The micropyle is formed by the inner integument and at anthesis, it is filled with an exudate secreted by the nucellar cap and inner integument. The exostomium is sealed by a hymen. The exudate and hymen probably function as surfaces for localized deposition of synergid-synthesized chemotropic agents. After fertilization the micropyle is occluded by a plug of flocculent material which appears to be more dense than the prefertilization material. This plug probably serves to preclude pathogen invasion and prevent desiccation of embryo and endosperm.

ISSN:0008-4026    

DOI:10.1139/b80-216

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The ultrastructure of the posteriorly uniflagellate zoospores ofSynchytrium macrosporumKarling, an obligate plant parasitic Chytridiomycete with a wide host range, is described. The zoospore possesses characteristic and intricate internal organellar associations involving the nucleus, mitochondria, microbody, lipid globule, endoplasmic reticulum, rumposome, and Golgi apparatus. The nucleus is in the anterior portion of the cell, and the lipid globule is in the posterior region. A complex microbody is between the nucleus and the lipid globule and branches out to partly encircle the nucleus, the lipid globule, and the mitochondria. A well-developed rumposome is in the posterior half of the cell, but a nuclear cap is absent. The rumposome is continuous with the rough endoplasmic reticulum, and is associated with a single dictyosome near the kinetosome. The rumposome encapsulates most of the exposed surface of the posterior portion of the lipid globule. Vacuoles have various shapes and contents, including some with the appearance of gamma bodies seen in other chytrids. A system of branched knobbed props links the kinetosome to the plasma membrane of the zoospore. The kinetosome and the secondary centriole are transversely striated, but no terminal plate is present. This study shows that the zoospore ofS. macrosporumhas a distinctive cell organization as compared withSynchytrium endobioticumand other chytrid zoospores.

ISSN:0008-4026    

DOI:10.1139/b80-217

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Reports on the mycorrhizal status of mosses have been scanty and inconclusive. We observed hyphae and vesicles resembling structures of vesicular–arbuscular (VA) mycorrhizal fungi within the mossFunaria hygrometricaHedw. growing on the soil surface of asparagus –Glomus epigaeuspot cultures. Controlled-environment experiments to determine whether moss is a potential host for VA fungi were conducted by inoculating moss cultures, asparagus plants, or combinations of moss and asparagus plants with chlamydospores ofG. epigaeus. Examination of cleared and stained asparagus roots and moss plants 10 weeks after addition ofG. epigaeusspores revealed typical arbuscules, vesicles, and hyphal coils in roots of asparagus grown alone or in combination with moss; hyphae, vesicles, and spores were seen in moss plants, but only in those grown with asparagus "companion" plants.Glomus epigaeuscolonization was widespread in moss stem and leaf tissue, and spore production was most prolific in senescent tissues. Similar endophytic structures and abundant sporulation occurred in the moss layer ofG. mosseaeandG. fasciculalusmoss-companion plant pot cultures. Although theFunaria–VA fungus association is apparently not a mutualistic one, the system may have ecological significance as well as potential for production of VA inoculum.

ISSN:0008-4026    

DOI:10.1139/b80-218

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The opening of archegonia was observed inPsilotumgametophytes from axenic culture. Contrary to earlier proposals that the outer neck cells break off, archegonial opening inPsilotumis similar to that of other pteridophytes. The rows of neck cells split apart to release the contents of the neck canal which clears a passageway from the egg to the outside. The movement of the rows of neck cells is unusual in that after separation they reflex and almost touch the gametophyte surface.

ISSN:0008-4026    

DOI:10.1139/b80-219

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Ancestral incompatibility relationships occur in populations of tristylous species ofOxalissectionIonoxalisin southern Mexico. Legitimate pollinations lead to substantial seed production; illegitimate pollinations result in complete failure of seed production in most cases. Modifications of trimorphic incompatibility which have led to the evolution of distyly in northern populations ofO. alpinawere not detected in populations of the southern Mexican species. Rapid genomic changes which have occurred during the northward migration ofOxalisspecies apparently have been accompanied by the spread of incompatibility modifiers favoring the evolution of distyly.

ISSN:0008-4026    

DOI:10.1139/b80-220

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Major gene resistance (hypersensitivity) to white pine blister rust can be detected on cotyledons of inoculated sugar pine seedlings shortly after germination. The cotyledon test reduces the time required for evaluating resistant genotypes from a few years to a few weeks.

ISSN:0008-4026    

DOI:10.1139/b80-221

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The role of certain abiotic and biotic factors in determining the structure of a post-fire ascomycete community was studied by the laboratory simulation of soil conditions occurring during and following a prairie fire. Aerated steam treatment of prairie soil (35, 40, 55, 70, or 85 °C for 60 s) was used to simulate the elevated soil temperatures generated during a grassland fire. Further manipulations included: (1) addition of ashed remains of prairie grasses to steamed soil surfaces, (2) the incubation of steam-treated soil samples layered over untreated prairie soil, and (3) addition of ash to steamed soil underlain with a layer of untreated soil to create a simulated burn.Across all treatments, species diversity and total number of species were significantly higher in soils steamed at 35, 55, or 70 °C than soils steamed at 40 or 85 °C. The greatest number of species per sample for steaming alone occurred in samples treated at 55 °C. The addition of ash to steamed samples or layering with untreated prairie soil significantly reduced species diversity and total number of species as compared with steamed soil alone. When ash and a subsurface layer of untreated soil were applied together, species diversity, total number of species, and mean number of species for samples steamed at 55 or 70 °C, were significantly greater than when either treatment was added separately. It was found that a simulated burn at 55 or 70 °C promoted the development of a community which most closely resembled a naturally occurring post-fire ascomycete community. This suggested that the structure of the post-fire ascomycete community was in part determined by (1) species responses to elevated soil temperatures, (2) ash deposition, and (3) biotic factors associated with the subsurface soil layers.

ISSN:0008-4026    

DOI:10.1139/b80-222

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The Asian, European, and North American serotypes ofGremmeniella abietinawere compared with 27 Vermont isolates using gel double diffusion and intragel cross absorption tests. An intermediate serotype, between the North American and European serotypes, was shown by means of cross absorption with antiserum prepared in response to a Vermont isolate. The majority of Vermont isolates resembled the Vermont intermediate in serological reaction, three resembled the European serotype, and two were of unknown serotypes. The serological data support possible hybridization betweenG. abietinaisolates in Vermont as well as the identification of a new serotype in Vermont.

ISSN:0008-4026    

DOI:10.1139/b80-223

出版商:NRC Research Press    

年代:1980

数据来源: NRC