摘要:

The primary zoospores ofLagenismacontain many peripheral "encystment vesicles." They disappear when the primary cyst wall is formed. The primary cyst wall consists of a 6-nm-thick, electron-dense layer and is secreted in less than 1 s. Ten seconds later, the flagella are retracted in the "straight-in way" within 3–4 s. The cyst bears spines which initially are filled with cytoplasm. They do not seem to contain cytoskeletal elements and possibly are shaped by a locally restricted extension of the cytoplasm and the cyst wall when the latter is formed. Later on, a secondary, inner, thicker fibrillar cyst wall layer is secreted. In contrast with other developmental stages studied hitherto, the vegetative primary cyst contains microbody-like structures.

ISSN:0008-4026    

DOI:10.1139/b78-148

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Fine structural details of antheridia and oogonia, of cytogamy, plasmogamy, and karyogamy, and finally of the development of the oospore are described. Sexually determined zoospores (most probably zoomeiospores) resemble vegetative primary zoospores (zoomitospores). They form gametangia (antheridia or oogonia) which are similar to vegetative primary cysts. An antheridium germinates with a fertilization tube which penetrates the oogonium. As seen in abnormal cell fusions, the tip of the fertilization tube opens only within an oogonium; presumably, its wall is disintegrated by the latter. Before plasmogamy, both plasmalemmata are closely appressed. The fused protoplasts move into a short zygotial hypha which protudes from the oogonium. The thick-walled oospore is formed herein. It includes nearly all of the cytoplasm of the gametangia. Karyogamy takes place within the developing oospore. It is initiated by an interdigitation of microtubules radiating from the centrioles and by a close association of the latter. The observations are compared with those on other developmental stages ofLagenismaand with those on gametangia and oospores of other Oomycetes.

ISSN:0008-4026    

DOI:10.1139/b78-149

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The occurrence and distribution of cellular slime molds in Alaska were investigated. Particular emphasis was given to tundra soils since this habitat was not previously explored for cellular slime molds. Isolations were also made from the white spruce – aspen forest of the interior forest region and the western hemlock – Sitka spruce forest of the southeast coastal forest region. Three speciesDictyostelium mucoroides, D. sphaerocephalum, andD. giganteumoccur in tundra. The first two species are common and frequently very abundant indicating that cellular slime molds play an active role in tundra ecology. Six other species were found in forest soils. One,Dictyostelium septentrionalis, was found for the first time and is described as a new species. It is distinctive for its size and optimum growth temperature, which is below 20 °C. The study completes the investigation of the latitudinal distribution of cellular slime molds in the northern hemisphere, establishing their occurrence north of the Arctic Circle.

ISSN:0008-4026    

DOI:10.1139/b78-150

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

On intact leaves of two cultivars (cv.) of rapeseed, Midas (Brassica napus) and Torch (B. campestris), conidia ofAlternaria brassicaegerminated at a rate of 12.1% and 19.5%, respectively, at 9 h after inoculation. They germinated usually by producing either germ tubes or secondary conidia. Penetration of leaves byA. brassicaewas abundant at 24 h and occurred either with or without the formation of appressoria. Penetration of cv. Torch leaves by the fungus occurred either directly through epidermal cells or indirectly through stomata, while cv. Midas leaves were penetrated almost exclusively through stomata. Blackspot lesions developed within 48 h after inoculation.Conidia ofNectria inventarequired at least 24 h to initiate germination and 4 days to parasitizeA. brassicaeon intact leaves. Therefore,N. inventadid not prevent primary infection of the leaves byA. brassicae. Instead,N. inventasuppressed the vegetative growth and sporulation ofA. brassicaeon excised rapeseed leaves.

ISSN:0008-4026    

DOI:10.1139/b78-151

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Conidia ofAlternaria brassicaeleaked various amino acids and sugars when they were exposed to an alternate dry–wet condition; the longer the drying period, the larger the amount of leakage. Among the amino acids, glutamine was exuded in the largest amount, followed by aspartic acid and glutamic acid. The sugar fraction consisted mainly of glucose and fructose. These leaked nutrients stimulated germination and growth of the mycoparasite ofA. brassicae, Nectria inventa. As a result, the germination rate ofAlternariaconidia was drastically reduced to less than 5% and they were eventually destroyed byN. inventa. In the absence ofN. inventa, however, conidia ofA. brassicaegerminated at the rate of 93.7% after being dried for 12 h at 32% RH.

ISSN:0008-4026    

DOI:10.1139/b78-152

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

A newHypoxylonspecies with ridge-like ornamentation on the ascospore,H. chestersii, is described. The fungus was collected in Wales.

ISSN:0008-4026    

DOI:10.1139/b78-153

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Extracts of developing soybean (Glycine max(L.) Merr.) cotyledons contained glutamate synthase activity (EC 2.6.1.53). The enzyme apparently was soluble and could be separated from glutamate dehydrogenase and NADH oxidase. Optimal synthase activity was at pH 7.8 in phosphate buffer. The enzyme was specific forL-glutamine as nitrogen donor and α-ketoglutarate as nitrogen acceptor. Activity was much greater with NADH than NADPH as reductant and evidence was obtained which indicated that the latter activity was an artifact in thein vitroassay owing to the presence of pyridine nucleotide phosphatase activity. Synthase activity was not reversible but was influenced by the addition of NAD+to the reaction mixture. The synthesis of [14C] glutamate by crude extracts was also detected with ferredoxin as electron donor. The role of glutamate synthase in providing α-amino N for amino acid synthesis in the developing legume seed was further clarified.Glutamate dehydrogenase (EC 1.4.1.3) activity was also measured in the cotyledons and its possible role in NH4+metabolism was discussed.

ISSN:0008-4026    

DOI:10.1139/b78-154

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Young seedlings ofMyrica galeL. grown in water culture were inoculated with a nodule suspension containing the effective actinomycete which induced root nodule formation. Nodule development was followed from initiation to nodule lobe formation and nodule root development using living materials and fixed nodules sectioned for light microscopy. After root hair infection and prenodule formation, three stages were observed: nodule lobe formation, a transition or arrested state, and nodule root development. The primary nodule lobe meristem originates endogenously and its formation involves pericycle, endodermis, and cortical cell derivatives. The lobe develops slowly to about 2 mm in length while the cortical cells are invaded by the actinomycete endophyte. After a period of arrest of variable duration, from a few days to several weeks, the nodule lobe meristem begins altered development, forming the elongate nodule root which undergoes slow but continuous growth to about 3- to 4-cm final length. New nodule lobe primordia are initiated endogenously at the base of existing nodules lobes, ultimately forming a cluster of nodule roots. Each nodule root, which elongates at about 0.1–1.0 mm per day, has a terminal apical meristem with reduced root cap formation and produces a modified root structure possessing an elaborate cortical intercellular space system and a reduced central cylinder. Nodule root growth is distinctive in that it shows strong negative geotropism. The endophyte is restricted to cortical cells of the nodule lobe and is totally absent from tissues of the nodule root. A probable role for nodule roots is to facilitate gas diffusion to the nitrogen-fixing endophyte site in the nodule lobe when nodules occur under conditions of low oxygen tension.

ISSN:0008-4026    

DOI:10.1139/b78-155

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Nitrogenase activity (acetylene reduction) and oxygen uptake by root nodules ofMyrica galeL. were measured before and after removal of nodule roots. There was no significant effect of nodule root removal when respiration was measured in the gas phase (0.05–0.2 atm pO2(1 atm = 101.325 kPa)) or acetylene reduction in a stirred aqueous phase at 0.2 atm pO2. However, when acetylene reduction was measured in 0.05 atm pO2in an unstirred aqueous phase, there was a 66 to 76% reduction in activity. These results indicate that nodule roots are important for oxygen uptake when the nodules are present in an aqueous phase at low pO2, which is probably the normal environmental conditions for many of the nodules. Other measurements showed that diffusion of oxygen from the shoot to the root nodules is not important for nitrogen fixation. These measurements were done on whole plants with the shoots in air (0.20 atm pO2) and the roots in water at the desired pO2value. With 0.0 atmpO2in the root environment, the rate of acetylene reduction was only 4% of the rate at 0.2 atmpO2. Thus, only small amounts of oxygen are transported from the shoot to the nodules.

ISSN:0008-4026    

DOI:10.1139/b78-156

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The pollen morphology of four species ofMyriophyllumfrom northwestern North American populations is described from studies using bright-field, interference-contrast, and scanning electron microscopy. Results indicate thatM. verticillatum, M. heterophyllum, andM. hippuroidescan be determined to species on the basis of pollen morphology.Myriophyllum spicatumandM. exalbescensare not readily separated on pollen morphology, although two tentative differences are suggested for further testing. It is also concluded thatM. verticillatumshould be recognized as a species clearly distinct fromM. spicatum.

ISSN:0008-4026    

DOI:10.1139/b78-157

出版商:NRC Research Press    

年代:1978

数据来源: NRC