摘要:

Segments of seedlings of susceptible and resistant lines of Triticineae were infectedin vitroby a virulent strain ofCercosporella herpotrichoidesFron. Samples were taken 4 days after inoculation and examined using scanning electron microscopy. In susceptible lines, a strong adhesion and an important development of the mycelium occurred in contact with the coleoptile. Simultaneously, a massive sporulation was observed. Conversely, in resistant lines, the hyphal stroma remained loose and poorly developed and failed to sporulate. A cytochemical and ultrastructural study of the walls of host cells showed changes in texture and an important deposition of strongly reactive compounds. These components could not be extracted by the usual solvents of matrix constituents of both cellulosic and lignified cell walls. An enhanced synthesis of such substances could prevent the action of the parasite glycolytic enzymes and therefore stop the fungal invasion. The wall, or at least some of its components, seems to be implicated both in the recognition of the pathogen by the host and in the triggering of a response leading to sequestration of the latter and arrest in its development.

ISSN:0008-4026    

DOI:10.1139/b85-110

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Young archegonia ofMarsilea vestitawere subjected to a weak cooling from 24 °C (optimum temperature) to 16 or 12 °C. The female gamete rapidly reacts to this treatment by ultrastructural modifications of various organelles. The enlarged plastids lose their starch and a great number of plastoglobuli are always observed in the stroma; they contain a poorly defined lamellar system with very few grana structures. Some mitochondria break down and assume a vacuolar appearance; the endo-membranous system is very abundant: numerous endoplasmic reticulum profils as well as a great number of dictyosomes appear. Ribosomes become indistinct and it is impossible to distinguish polysomes in the hyaloplasm. The fertilization cone, which is used by the spermatozoid during its moving towards the female nucleus, is normally funnel shaped. After the treatment it is changed into a basal area spreading along the cell sides and separated from the remaining part of the gamete by a more or less continuous envelope of neoformed endoplasmic reticulum. Finally, it is possible by this treatment to remove the usual barrier to polyspermy and to observe several spermatozoids in the female cytoplasm.

ISSN:0008-4026    

DOI:10.1139/b85-111

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Synthesis from UDP-[14C]glucose of charged lipid-linked glucosyl compounds by pea membranes was short-lived and of very limited magnitude compared with the synthesis of 1,4- and 1,3-linked β-glucans. Chromatographic and chemical behaviour of lipid-linked monophosphoryl glucose (Lip-P-glc), the only charged lipid formed at initial stages (30 s), was similar to that of authentic dolichol monophosphoryl glucose (Dol-P-glc). Lip-P-glc exhibited no turnover during pulse-chase experiments. Lipid-linked pyrophosphoryl glucose or pyrophosphoryl oligosaccharides were not detected. Coumarin (10 mM) caused a severe inhibition of the synthesis of sodium dodecyl sulfate soluble products and alkali-soluble and alkali-insoluble glucans, without affecting the rate of synthesis of Lip-P-glc. Transfer of the label from endogenous Lip-P-[14C]glc or from authentic Dol-P-[3H]glc into nonlipid products was minimal. It is concluded that the lipid-linked phosphoryl saccharide formed from UDP-glucose is not an obligate intermediate in the formation of β-glucans in pea membrane preparations.

ISSN:0008-4026    

DOI:10.1139/b85-112

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Although the generaCistus,Fumana,Helianthemum, andTuberaria, all Cistaceae, have been shown to form ectomycorrhizae in the Old World, no species of Cistaceae has been reported to do so in North America. In this study three species ofHelianthemum, two ofHudsonia, and two ofLechiaoccurring in North America were collected and examined for mycorrhizal infections. All species showed some evidence of ectomycorrhizae. Although it was difficult to determine the fungi responsible, constant plant–basidiomata associations suggest that ectomycorrhizae in North American Cistaceae may be formed by species ofAmanita,Astraeus,Cenococcum,Inocybe,Laccaria,Leccinum,Russula,Scleroderma, andThelephora.

ISSN:0008-4026    

DOI:10.1139/b85-113

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Previous results had suggested that Ca(H2PO4)2may be directly inhibitory to host penetration from appressoria ofErysiphe graminisf. sp.hordeiand that Ca and P are found in much higher amounts in oversized papillae (resistant to penetration) than in normal papillae (not resistant to penetration). In the present study, chlortetracycline was used as a calcium-selective fluorescent probe to examine the occurrence and distribution of calcium in papillae of barley coleoptile epidermal cells. When stained with chlortetracycline, normal and oversized papillae fluoresced bright yellow, indicating the presence of calcium. Oversized papillae, produced in the presence of calcium phosphate solution, could be either poststained or stained during papilla formation by including chlortetracycline in the incubation medium. Such attempts to stain normal papillae during their formation in the presence of calcium nitrate resulted in the formation of oversized papillae similar in appearance to those produced in the presence of Ca(H2PO4)2; however, penetration from appressoria was not inhibited by chlortetracycline. In some cases, this treatment resulted in the formation of chlortetracycline-fluorescent wall appositions on lower periclinal cell walls far removed from the fungus; these appositions were interpreted as calcium-containing wound plugs. None of the chlortetracycline-associated phenomena were seen without calcium in the incubation medium. These results confirm the occurrence and demonstrate the distribution of calcium in papillae and show that chlortetracycline, like phosphate, can act in conjunction with calcium to enhance secretion of papilla material.

ISSN:0008-4026    

DOI:10.1139/b85-114

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The fate of15N from the amino group of labelled asparagine was followed in growing pea leaves, in the presence and absence of inhibitors of deamidation (DONV, 5-diazo-4-oxo-L-norvaline) and transamination (AOA, aminooxyacetate). The label was widely incorporated into various amino acids, especially aspartate, glutamate, alanine, and homoserine, as well as glycine and serine. Treatment with AOA considerably decreased the label of all these amino acids except aspartate, consistent with the production of the latter by deamidation of asparagine. This was confirmed by the use of DONV, which decreased aspartate labelling by over 70%; a similar decrease in glutamate labelling suggested that the latter was labelled predominantly by transamination of aspartate. In contrast, DONV had a much smaller effect on the labelling of alanine, homoserine, glycine, and serine, indicating a direct transfer of amino nitrogen from asparagine, rather than transfer from aspartate (or glutamate). The labelling of glycine and serine and the transfer of amino nitrogen to ammonia and glutamine (amide group) were consistent with a flow of asparagine nitrogen into the photorespiratory nitrogen cycle. During leaf expansion there was a decrease in the amount of asparagine metabolised, and a decreasing participation of deamidation as the leaf matured.

ISSN:0008-4026    

DOI:10.1139/b85-115

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Seeds ofHyptis suaveolenswere sorted into three weight classes and exposed to either red light at different fluence rates or to mixtures of red and far-red light, at two constant temperatures. At the higher temperature tested, the fraction of smaller seeds required at least 10 times more energy for full germination under red light than the larger seeds. Larger seeds germinated fully even under pure far-red light, while the smaller ones required a calculated proportion of 80% active phytochrome to attain comparable germination percentages. It is suggested that different sized seeds could be favoured in different natural microenvironments.

ISSN:0008-4026    

DOI:10.1139/b85-116

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Sinker cells showed ultrastructural similarities in three species ofArceuthobiumon three different hosts despite differences in season of collection and fixation. All species had abundant osmiophilic lipid bodies, plastids with prolamellarlike bodies, mitochondria with large nucleoids, chromocentric nuclei, and peculiar saccules associated with plasmodesmatal fields. Xylem may not be continuous through sinkers. Apoplastic continuity between host and parasite is afforded by fused cellulosic cell walls. Pitlike wall thinnings and "half-plasmodesmata" are found between juxtaposed host and parasite cells. One-sided, imperforate sieve pores were noted between a sieve cell and a contiguous sinker cell. However, symplastic isolation of the host and parasite seems likely. Therefore, nutrients may be absorbed from the common host–parasite apoplast. Mobilization of nutrients out of the endophytic system to the aerial shoots is thought to be facilitated by differential starch storage in the parasite body.

ISSN:0008-4026    

DOI:10.1139/b85-117

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The photosensitization of the cereal pathogenFusarium culmorumby phenylheptatriyne (PHT), a naturally occurring acetylene ofBidens pilosaL. (Asteraceae), was investigated. PHT strongly inhibited germination of macroconidia (mean effective concentration (EC50) = 1.7 ppm) and growth of mycelia (EC50 = 5.6 ppm) ofF.culmorumin the presence of near-ultraviolet radiation. Photosensitization of macroconidia was found to be fungicidal and was not reversed after repeated washings in PHT-free media. Photosensitization was less apparent in germ tube elongation in liquid media. However, nonphotosensitizing growth inhibition was observed in these trials. Endogenous levels of PHT inBidens pilosawere highest (up to 450 μg/g fresh weight) in all plant parts during the seedling stage and declined during vegetative growth. The concept that PHT acts as a preinfectional inhibitor toF.culmorumis discussed.

ISSN:0008-4026    

DOI:10.1139/b85-118

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Changes in the anatomy, morphology, and stored food reserves of stratifying (5 °C) sugar maple embryos were followed from a strongly dormant state through germination. The correlation of cell division and cell elongation with radicle protrusion was also investigated. No morphological or anatomical changes were observed before first maturation of phloem elements on the 17th day of stratification. Mature xylem elements were first observed on day 37, and first germination was noted on day 38. Radicle protrusion was initiated by cell elongation, and cell division was not active for several days after emergence and a marked increase in lengths of the axes had occurred. Changes in amounts of protein, lipid, and starch were not observed during the stratification period, but mobilization of stored reserves was clearly evident with emergence of the radicles. Several of these key events appeared to be closely associated with previously described peaks and patterns of growth regulator activity.

ISSN:0008-4026    

DOI:10.1139/b85-119

出版商:NRC Research Press    

年代:1985

数据来源: NRC