摘要:

Most species of plants are normally infected by mycorrhizal fungi, but some plant taxa do not usually form generally recognisable mycorrhizas. The identity and relationships of these "nonmycorrhizal" or weakly mycorrhizal taxa are considered in this review. Mechanisms that are used by the plants for avoiding infection are discussed. Exudation of fungitoxic compounds or simply low levels of exudation are not believed to inhibit infection. Similarly, the presence of fungitoxic compounds in root cortex cells is not believed to prevent mycorrhizal fungi from infecting weakly mycorrhizal plants. It is proposed that the control of mycorrhizal fungal penetration is exerted by interactions between the organisms at the level of the cell wall and (or) middle lamella.

ISSN:0008-4026    

DOI:10.1139/b87-051

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Stichococcus bacillarisNaeg. (Chlorophyceae) grown on a 12 h light: 12 h dark cycle divides synchronously under photoautotrophic conditions and essentially nonsynchronously under mixotrophic conditions. Photoassimilation of carbon under photoautotrophic conditions was followed by a decline in cell carbon content during the dark period, whereas under mixotrophic conditions cell carbon increased throughout the light–dark cycle. The rates of nitrogen assimilation by cultures grown on either nitrate or ammonium declined sharply during the dark, and these declines were most pronounced under photoautotrophic conditions. Photoautotrophic cells synthesized glutamine synthetase and NADPH – glutamate dehydrogenase (GDH) exclusively in the light, whereas in mixotrophic cells about 20% of the total synthesis of these enzymes during one light–dark cycle occurred in the dark. NADH–GDH was synthesized almost continuously over the entire light–dark cycle. In the dark, both under photoautotrophic and mixotrophic conditions, the alga contained more than 50% of glutamine synthetase in an inactive form, which was reactivatedin vitroin the presence of mercaptoethanol andin vivoafter returning the cultures to the light. The thermal stability of glutamine synthetase activity was less in light-harvested cells than in dark-harvested cells. The inactivation of glutamine synthetase did not occur in cultures growing either heterotrophically in continuous darkness or photoautotrophically in continuous light. This enzyme appears to be under thiol control only in cells grown under alternating light–dark conditions, irrespective of whether this light regime results in synchronous cell division or not.

ISSN:0008-4026    

DOI:10.1139/b87-052

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Hypogeous fungal sporocarps were collected over 32 months in a 35- to 50-year-old Douglas-fir stand in western Oregon. Production of the 9 ascomycete and 21 basidiomycete species collected during the study was dominated by a few species,Gautieria monticola,Hysterangium crassum,H.coriaceum, andMelanogastersp.nov., each accounting for 5% or more of total annual dry weight. Estimates of annual productivity ranged from 2.0 to 3.2 or 22.0 to 35.4 kg dry weight/ha, depending on the method of calculation. Peaks in production were generally attributable to one or two species. Pronounced seasonal trends in production were not evident, although standing crops decreased in winter. The annual fruiting period of species varied from 3 to 11 months.

ISSN:0008-4026    

DOI:10.1139/b87-053

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The flowering cycle ofSymplocarpus foetidusin volves 2 years. During the 1st year, the different flower parts are formed. The spadix, spherical at the beginning, elongates gradually to an ovoid–cylindrical shape. The flower primordia take a quadrangular shape when the four perianth parts and stamens are beginning to differentiate. In the first stages of its growth, the developing ovary is in a superior position. At the end of its growth, as a result of the type of development of the flower ofSymplocarpus, it becomes completely inferior. Generally, at the end of the 1st year of the flowering cycle, the gynoecium consists of a small protuberance at the top of the unilocular ovarian cavity. During the 2nd year, the ovary closes and penetrates into the axis, the style forms, and the unique suborthotropic ovule develops. Our study of the flower's organogenesis shows that the inferior position of the ovary does not result from an invagination of the aerenchyma of the inflorescence axis although the ovary is completely enclosed in the axis of the inflorescence at maturity. The analysis of serial sections shows that the tissue of the flower originates from an organogenic zone distinct from the aerenchyma of the inflorescence axis.Symplocarpusis the only Araceae to possess an inferior ovary. The authors consider this genus to be an advanced genus in this family.

ISSN:0008-4026    

DOI:10.1139/b87-054

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The structure of the kinetosomes of zoospores of the Babraham isolate ofNeocallimastix(N.patriciarum, previously described asN.frontalis) both free and in the later stages of zoosporogenesis have been determined from electron micrographs of thin sections. The zoospores have up to 20 flagella. At the base of each, within a circular ridge of the plasma membrane, is a circumflagellar ring. There are no props connecting the triplets of the kinetosome to the plasma membrane, but there are two connections from the skirt around the kinetosome to the circumflagellar ring. In developing zoospores, within sporangia, the circumflagellar ring is perpendicular to the long axis of the flagellum, but in free zoospores it is tilted at an angle of about 60°. The skirt is continued proximally to form a cowl-shaped structure below the kinetosome. The spur has longitudinal and transverse components; microtubules radiate from both. Some microtubules intersect the nucleus, but there is no specific association. The classification ofNeocallimastixis discussed.

ISSN:0008-4026    

DOI:10.1139/b87-055

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Reproductive buds and developing inflorescences were collected weekly from mature trees during three successive growing seasons in northwestern Ontario. Material was prepared to show all stages of inflorescence and flower development and meiosis. Male inflorescence induction, involving the long-shoot bud apex and one or two proximal axillary apices, occurred in early May, before bud burst. Female induction involved the short-shoot bud apex and occurred in late June – early July. Both male and female partial inflorescences resembled a simple dichasium. The male flower consisted of usually two stamens and two or three tepals variably arranged. Meiosis occurred in late July – early August. Each female flower consisted of two stigmas, two connate tepals that were not noticeable at maturity, and a parietal placenta bearing two unitegmic ovules. Meiosis occurred in mid-June, after pollination in mid-May. It is concluded that developmental data do not help elucidate whether the inferior portion of the gynoecial wall is cauline or appendicular and whether the placenta is derived from axial or carpellary tissue. It is suggested that the trigger(s) evoking male and female inflorescence induction may be different and that the metabolic prerequisites for induction and early development would be supplied by winter-stored material for male development and by current metabolic processes for female development.

ISSN:0008-4026    

DOI:10.1139/b87-056

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

By using two-dimensional polyacrylamide gel electrophoresis, 10 additional pathogenesis-related proteins (b6c,b9c,b10a,b10b,b11a,b11b,b12,b13,b14,b15) were found in intercellular fluid extracts of stressed 'Xanthi-nc' tobacco leaf tissue. Proteins were identified as extracellular pathogenesis-related stress proteins by polyacrylamide gel electrophoresis analysis of three successive intercellular fluid extracts compared with homogenates before and after making intercellular fluid extracts. Four proteins (b12,b13,b14,b15) were only resolved by using native polyacrylamide gel electrophoresis for basic proteins in the first dimension gel and they were best extracted in 0.05 MTris–HCl (pH 7.5) and 0.05 MCaCl2as the infiltration buffer. The four basic proteins were found in intercellular fluid extracts from leaf tissue subjected to the same types of chemical inducers as previously described for tobacco pathogenesis-related proteins. Their accumulation was inhibited by basic amino acids or spermidine (1 mM) and they were resistant to endogenous and exogenous (trypsin, subtilisin) proteolysis. They did not bind to concanavalin A – Sepharose. These findings indicate that at least 23 proteins accumulate extracellularly after various types of stress in 'Xanthi-nc' tobacco green tissue. These proteins probably represent several groups or families of plant stress proteins.

ISSN:0008-4026    

DOI:10.1139/b87-057

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Stigmina zillerisp.nov. is described from a brown zonate leaf spot of broadleaf maple (Acer macrophyllumPursh) in southwestern British Columbia, Canada.

ISSN:0008-4026    

DOI:10.1139/b87-058

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The grassland community on serpentine soil was found to have vesicular–arbuscular mycorrhizae. Twenty-seven species made up the herbaceous cover; 23 were annuals. Two annual species were from nonmycorrhizal families, but one had some colonization. Twenty-five species had colonization in over half the length of the roots. Annuals had especially heavy colonization, which frequently filled the cortex of the root. Of the herbaceous cover in the community 98% was mycorrhizal; 97% was colonized in over half the length of the roots; and 91% was colonized in over three-fourths the length of the roots. The common fungal symbionts wereGlomus fasciculatumandGlomus tenue.

ISSN:0008-4026    

DOI:10.1139/b87-059

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

When intact oat coleoptiles (Avena sativavar. Harmon) were submerged in water, saturation of the water with CO2promoted their elongation but eliminated their phototropic response to blue light. Increasing the pH of the CO2-saturated water prevented the promotion of coleoptile elongation but did not prevent the elimination of the phototropic response. In air, phototropic curvature was significantly reduced by 10% CO2and was eliminated by 30%, without any reduction in growth. It is postulated that the increase in CO2concentration may eliminate the phototropic curvature of the coleoptile by preventing the light-induced inhibition of growth on the illuminated side of the organ. Possible mechanisms are briefly discussed.

ISSN:0008-4026    

DOI:10.1139/b87-060

出版商:NRC Research Press    

年代:1987

数据来源: NRC