摘要:

Yellowing of leaves is often an early and persistent symptom of plants infected with vascular wilt fungi. This symptom is also characteristic of senescence and hence the cytokinin levels in healthy andVerticillium-infected tomato plants were investigated. Tomato plants (Lyeopersicon esculentumL. cv. Bonny Best) were inoculated with the fungusVerticillium dahliaeKleb. 49 days after seeding. At intervals after inoculation, cytokinin levels in root xylem exudate were determined in healthy and infected plants. Cytokinin concentrations (per plant and per millilitre of exudate) were similar in healthy and infected plants at days 50 and 55 but were lower in infected plants at days 61 and 65 owing to reduced concentrations of both free and bound forms of cytokinin. Infected plants first showed visible symptoms of chlorosis on older leaves at day 56. By day 61 the lower three to five leaves were obviously wilted and chlorotic and by day 65 wilt and chlorosis were apparent on most leaves on the lower half of the shoot. Whether the first chlorotic symptoms in infected plants were due to the concomitant reduction in cytokinin concentrations was not resolved. However, the consistently lower concentrations of cytokinin in infected plants after the onset of symptoms are presumed to contribute significantly to the continued rapid loss of chlorophyll measured in older leaves and the progressive development of visible chlorosis in younger leaves. Reduced water potentials in leaves and fungal activity in infected roots are likely to be among factors responsible for the reduction in cytokinin concentration in infected plants.

ISSN:0008-4026    

DOI:10.1139/b77-048

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Five new species ofDelitschiafrom Venezuela are described and photographed. These areD. dochmiophragmaon dung of horse,D. ionthadaon dung of burro,D. mesostenosporaon dung of burro,D. sexdecimsporaon dung of horse, andD. spiralirimaon dung of cow. The genusDelitschiais restricted to species in which the bitunicate asci have dark, two-celled ascospores, each cell being provided with an elongated germ slit, surrounded by a gelatinous sheath. Additional records are included for three previously described species.

ISSN:0008-4026    

DOI:10.1139/b77-049

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The existence of two major types of lichen woodland in Canada,Cladonia stellariswoodland andStereocaulon paschalewoodland, is discussed in relation to their seral nature and their rarely developed theoretical climax type.Our own observations, coupled with previous descriptions from a wider area, suggest thatStereocaulon paschalewoodland replacesCladonia stellariswoodland in a more or less continuous zone from just west of Churchill across to Great Slave Lake, immediately north and south of latitude 60° N. Both woodland types are often typical of sandy soils (pH 6 or less) and almost always represent the final recovery phase after fire. Rarely, the lichen surface is replaced by a continuous moss cover as the spruce canopy closes. The lichen surface is thus dependent on the lack of competition from higher plants, the absence of which is characteristic of the climate of this northern boreal region.Cladonia stellariswoodland also occurs on palsas and peat plateaux where, again, lack of higher plant competition and a suitable pH exist.The recovery sequence after fire is a highly complex process and as yet only the following parameters have been categorized. In the early recovery phases, limited soil moisture and hence a reduced summer latent heat flux enhance the sensible heat flux. The surface conditions are analogous to those of a hot desert with very high surface temperatures and extremely large diurnal temperature fluctuations. The physiology of these initial moss and lichen colonizers presumably enables them to tolerate these harsh conditions. The establishment of a few spruce seedlings and the subsequent development of open lichen woodland modulates the harsh summer temperature regime and allows the further development of a vegetated surface. After humus accumulation, which acts as an effective mulch, summer soil moisture is elevated, enhancing the latent heat flux and correspondingly reducing the sensible heat flux. This probably allows the full development of mature lichen woodland with its almost monospecific ground cover of eitherCladonia stellarisorStereocaulon paschale. Limited data suggest that the net photosynthetic responses of these two species is favoured by the relatively warm mesic conditions established by the open spruce canopy. Good accumulation of snow in the winter is probably also important for protection of the lichen surface from low temperatures. The open nature of mature lichen woodland is apparently maintained by an active inhibition of spruce seedling establishment by the lichen mat, although the mechanism is not entirely clear.

ISSN:0008-4026    

DOI:10.1139/b77-050

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The epiphyllous appendages arise from the two outer cell layers of the young leaf by a cell division pattern like that of leaf inception at the shoot apex. The leaf-like appendages, especially, show a developmental pattern that resembles that of the main leaf. These data as well as anatomical evidence provide a factual basis for homologizing the leaf-like appendages with leaves (phyllomes). Only the position of the leaf-like epiphyllous appendages contradicts that of typical phyllomes. This contradiction disappears by applying the evolutionary process of spatial shifting (heterotopy) to leaves. This process leads to the formation of epiphyllous leaves which may be contrasted with cauline leaves. Since secondary appendages have been observed on some of the epiphyllous leaves, the concept of a 'leaf system' is used in contrast with the concept of ‘shoot system.’ In a leaf system leaves are interconnected without the intervention of a shoot apex. Supporting evidence from experimental research, especially organ culture, is pointed out. Other unusual modes of plant construction are briefly discussed.

ISSN:0008-4026    

DOI:10.1139/b77-051

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The growth ofSphagnum nemoreumScop, and the fine structure of its leaf cells were studied in aseptic cultures to which were added lead, cadmium, arsenate, and fluoride (0.001, 0.01, 0.1, and 1 mMsolutions). The highest concentration having no or almost no effect on the dry weight was 0.1 mMfor lead, 0.01 mMfor fluoride and cadmium, and 0.001 mMfor arsenate. The 1 mMsolution of Na2HAsO4and 0.1 mMsolution of CdSO4were toxic and the inocules died rapidly. The 1 mMsolutions of KF and Pb(NO3)2were growth-retarding. The chloroplasts tended to accumulate starch when arsenate (0.1 mM) was added to the medium. Fluoride promoted the development of plastoglobuli, and lead (0.1 mM) promoted lipid accumulation in the cytoplasm. High concentrations of arsenate and fluoride inhibited the differentiation of hyaline cells. The physiological and ecological effects of these substances have been discussed with special reference to the problem of pollution.

ISSN:0008-4026    

DOI:10.1139/b77-052

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The ultrastructure of gametangial development and oospore formation was studied inPhytophthora megaspermavar.sojae, a species with the paragynous antheridium. Except for the early gametangial interaction, the developmental stages of oogonial expansion, fertilization tube formation, oosphere and oospore formation were very similar to those reported for amphigynous species. The initial contact differs in the two types of gametangial interaction in that in amphigyny the oogonial hypha contacts and penetrates the antheridial initial from the side, whereas in paragyny the antheridial hypha touches and fuses with the oogonial initial from the side without penetrating it. In both cases the end result seems to be the same: the establishment of a firm adhesion zone between the gametangia. Dictyosome-derived vesicles were active in the formation of the contact zone, during oogonial expansion and wall thickening, and during extension of the fertilization tube. An extensive conversion of cytoplasm occurred during differentiation within the oogonium from a largely 'functional' cytoplasm rich in mitochondria, ribosomes, rough endoplasmic reticulum, and dictyosomes to a largely 'storage' cytoplasm within the oospore consisting of an ooplast and surrounding lipid layer.

ISSN:0008-4026    

DOI:10.1139/b77-053

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

TheVerticilliumstate ofNectria inventais a destructive parasite ofAlternaria brassicae. Tropic growth of parasite hyphae towards hyphae and conidia ofA. brassicaeoccurs in the vicinity of the host. Upon contact, the parasite hyphae often form appressorium-like bodies on the host cells and produce fibrous adhesive material at the host–parasite interface. Conidia are penetrated more commonly than hyphae. Penetration of the septa in hyphae results in a separation of cells. Penetration of a mature conidium also occurs commonly at a septum. The presence of a large hole in the wall of the host cell and the meshwork of material at the penetration site suggest that enzymatic breakdown of host cell wall occurs. Juvenile conidia are penetrated usually at the basal pore.

ISSN:0008-4026    

DOI:10.1139/b77-054

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The endophyte of the haustorium inComandraand the tissues of the upper haustorium have a complex developmental and structural relationship with each other. Glands may be found near the tip of a young endophyte, providing evidence that the gland and surrounding tissues have been moved into the host as a unit. A distinct interrupted zone is present, traversed by a small number of unbranched vessels. Additionally, some apparently blind vessels in the more central portion of this zone are occluded with fibrous material which seems to be secreted by vesicles in the adjacent parenchyma. Advance into the host seems to involve crushing host cells and subsequent absorption of cell contents. It is suggested that superficial digitate cells are also crushed and that the lytic enzymes thus liberated play a role in the attack on host cells. The dark-staining non-cellular layer delimiting many parts of the endophyte seems to be made up of crushed cell walls from both partners. No cytoplasmic connections between host and parasite have been observed. Mature xylem contacts may be abutments in pit areas of host vessels or actual invasions of the latter, often with cell divisions within such invaded tracheary members. The function of the gland remains obscure.

ISSN:0008-4026    

DOI:10.1139/b77-055

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

Acid phosphatase (orthophosphoric-monoester phosphohydrolase (acid optimum), EC 3.1.3.2) has been localized in cells at the growing tips of the endophyte in the semiparasitic angiospermComandra umbellata. Lysosomes in tip cells release their contents into the apoplast at the host–parasite interface before any possible release of enzyme from disrupted host lysosomes. However, a large-scale digestion of host cells does not occur. Parasite cells release acid phosphatase and probably other lysosomal enzymes which appear to disrupt host cell membranes causing a loss in turgor pressure followed by the eventual crushing of host cells by the invading endophyte.

ISSN:0008-4026    

DOI:10.1139/b77-056

出版商:NRC Research Press    

年代:1977

数据来源: NRC

摘要:

The major flavonoid complement of leaves of the polyploid seriesPotentilla finitimaKohli & Packer (2n = 14),P. pensylvanicaL. (2n = 28), andP. bipinnatifidaHook. (2n = 56) has been determined. Eleven flavonoid glycosides have been identified and their distribution within the polyploid series plotted and discussed. Evidence is presented for the occurrence of a 'recombinant' flavonoid in the speciesP. pensylvanicaL.

ISSN:0008-4026    

DOI:10.1139/b77-057

出版商:NRC Research Press    

年代:1977

数据来源: NRC