摘要:

Feedback control of enzymes in the pathway for the biosynthesis of aspartate-family amino acids was examined usingGlycine maxcallus, suspension cultures, and seedlings to determine if the controls are different in the three systems. Aspartate kinase activity (EC 2.7.2.4) derived from soybean cell suspension cultures is 50% inhibited by 1.0 mML-threonine and 50% inhibited by 1.0 mML-lysine. In contrast, aspartate kinase activities from 3-day-old seedling cotyledons and from callus cultures grown from cell suspension cultures are inhibited approximately 70% by 1.0 mMthreonine and 30% by 1.0 mMlysine. These data and chromatographic data indicate that different ratios of a lysine-sensitive and a threonine-sensitive aspartate kinase enzyme can occur in soybean cotyledons and callus as compared with cell suspension cultures. Threonine (1 mM) inhibited homoserine dehydrogenase activities (EC 1.1.1.3) from cotyledon and cell suspension cultures approximately 67 ± 2% while the activity from callus was inhibited slightly more (77 ± 1%). Four forms of homoserine dehydrogenase activity were detected on electrophoretic gels containing cotyledon extracts, while only three of these forms of homoserine dehydrogenase activity were detected in extracts of callus and cell suspension cultures. The threonine-insensitive form disappeared, while the three threonine-sensitive forms were still present. Dihydrodipicolinate synthase activities (EC 4.2.1.52) from all three sources were at least 95% inhibited by 1.0 mMlysine. Only one form of this enzyme was detected on electrophoretic gels.

ISSN:0008-4026    

DOI:10.1139/b79-041

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Photosynthetic responses of black and red spruce were used to define parameters of their fundamental niches. Grown at warm temperature, black spruce had highest rates of CO2uptake at high light intensities, fitting it for a pioneering role, while red spruce had the lowest light compensation point, fitting it for a late successional role. Black and red spruce responded in different ways to low temperature acclimation. Low temperature, low light (12 °C, 100 ft-c (1 ft-c = 10.764lx)) acclimation stimulated CO2uptake in black spruce under all conditions while it depressed CO2uptake in red spruce relative to rates following high temperature (26 °C) acclimation. Niches defined by photosynthetic responses corresponded to observed habitats in the area of sympatry of black and red spruce and demonstrated the existence of ecological isolation, a premating restriction to hybridization.Hybrids, backcrosses, and recurrent backcrosses of black and red spruce had lower rates of CO2uptake than one or the other species in all light and temperature environments tested. In most cases, the hybrid had lower rates than both species. Growth depends on photosynthesis and is one component of fitness. Therefore, negative heterosis in hybrids and hybrid derivatives represents another mechanism of reproductive isolation, the postulating barrier of hybrid adaptive inferiority. Selection against hybrids should be density dependent, explaining both their widespread occurrence in habitats opened by fire or logging and their paucity in closed stands.

ISSN:0008-4026    

DOI:10.1139/b79-042

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Penetration of sunflower,Heliantluis animus, root epidermal cells by zoospores ofPlasmopara halstediiis preceded by formation of a papilla on the inner surface of the host cell wall that invaginates the host plasma membrane. Localized degradation and penetration of the host cell wall by the pathogen follow. The invading fungus forms an allantoid primary infection vesicle in the penetrated epidermal cell. The host plasma membrane invaginates around the infection vesicle but its continuity is difficult to follow. Upon exit from the epidermal cell the fungus may grow intercellularly, producing terminal haustorial branches which extend into adjacent host cells. The fungus may grow through one or two cortical cell is after growing from the epidermal cell before it becomes intercellular. Host plasma membrane is not penetrated by haustoria. Intercellular hyphae grow toward the apex of the plant and ramify the seedling tissue. Resistance in an immune cultivar is hypersensitive and is triggered upon contact of the host cell with the encysting zoospore before the host cell wall is penetrated. Degeneration of zoospore cytoplasm accompanies the hypersensitive reaction of the host. Zoospores were often parasitized by bacteria and did not germinate unless penicillin and streptomycin were added to the inoculum suspension.

ISSN:0008-4026    

DOI:10.1139/b79-043

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Primary leaves of wheat (Triticum aestivumL.) with and without resistance genesSr5, Sr6, Sr8, orSr22were inoculated with avirulent races of stem rust (Puccinia graminisPers. f. sp.triticiEriks. & E. Henn.) and examined by fluorescence microscopy. In leaves containing theSr5gene for resistance, both epidermal and mesophyll cells fluoresced when interacting with the fungus, indicating incompatibility. In leaves containing theSr6gene, interacting epidermal cells did not fluoresce and incompatibility was expressed only in mesophyll cells.When the effect of theSr5gene was studied in leaves with different genetic backgrounds, it was found that most colonies developed only one or two haustorial mother cells in leaves containing this gene in Prelude, Marquis, or Reliance backgrounds, when examined up to 72 h after incubation. Conversely, in leaves with the Chinese Spring background, one-third of the colonies continued to grow and they produced macroscopically visible lesions. Our observations indicated that the Chinese Spring genotype partially altered the expression of theSr5gene in mesophyll but not in epidermal cells. In contrast, theSr6gene was more effective in the Chinese Spring background than in the Prelude background.Rust development in leaves with or without theSr8gene was the same up to 60 h after incubation, when incompatibility in resistant plants was first detected by the appearance of fluorescing host cells. By 72 h, mean colony size in resistant leaves was smaller than that in susceptible leaves, evidently because growth of runner hyphae was inhibited. Apparently, theP8gene for avirulence was not expressed until colonies had reached considerable size. In leaves containing theSr22gene for resistance, the sequence of histological events was similar to that in leaves containingSr8, but fluorescing host cells appeared later (72 h) and colony growth was inhibited only at 96 h after incubation. In both of these interactions, fluorescing host cells developed at the periphery of colonies when incompatibility was expressed. The host-parasite interaction in cells invaded before that time remained compatible even at later stages of colony development. In leaves containing theSr5or theSr8gene, but not in those with theSr6gene, the growth of some colonies was inhibited although they were not associated with fluorescing host cells. Evidently, host-cell necrosis was closely associated with reduced fungal growth in interactions involvingSr6, but not in interactions involving the resistance genesSr5andSr8.

ISSN:0008-4026    

DOI:10.1139/b79-044

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The observation of thick sections and serial thin sections with the electron microscope demonstrates a reticular organization of mitochondria in cultured cells fromGinkgo. Thick sections show that most of the mitochondria fuse either in loose networks made up of elongated elements or in dense clusters composed of globular units. Serial thin sections enable us to prove the true reticular nature of the mitochondrial organization; most of the mitochondrial profiles are part of highly fused and branched networks. These mitochondrial reticula (about two to three per cell) occupy an important place within the cell. Some mitochondria remain isolated or they fuse slightly. Two three-dimensional models have been built: the first one constructed with cardboard sheets is used to display the organization of a reticulum; the other of Plexiglas clearly indicates the relative positions and the form of mitochondria in a complete cell. The mitochondria, plastids, and vacuoles of this cell are also measured and enumerated.

ISSN:0008-4026    

DOI:10.1139/b79-045

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Field inoculation experiments were carried out to determine the pattern ofCeratocystis ulmiinfection of white elm (Ulmus americana). From April 7 to October 27, 1971, four methods of artificial inoculation were used to infect healthy, naturally occurring elm saplings approximately 56 km north of Sault Ste. Marie, Ontario. External and internal symptoms of Dutch elm disease, internal spread ofC. ulmi, and external damage by the disease were correlated with inoculation methods and seasonal morphological development of elm.The results suggested that the most susceptible period for successful artificial infection of white elm in 1971 was early June to late July. The beginning of the most susceptible period corresponded with the initiation of leaf expansion and large size of springwood vessels in the outer rings. It coincided with a change in accumulated degree days above 5.6 °C from minus to plus. A decline in susceptibility was found after August 12 when leaves were fully matured and 1971 buds had developed. Inoculations before June 3 resulted in the expression of wilting symptoms, always about June 24. This indicates that the disease development is highly dependent on host morphological and physiological conditions.The slit method of inoculation most closely simulated natural beetle infection. The modified Hagborg method of inoculation gave results similar to those of the slit method but required more effort and time in practice. The drill and chisel methods appeared too severe and resulted in the death of all trees inoculated from April 7 to August 12.

ISSN:0008-4026    

DOI:10.1139/b79-046

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Adults of the North American native elm bark beetle,Hylurgopinus rufipes, naturally infested with Dutch elm disease fungus,Ceratocystis ulmi, were caged on trunks of white elms (Ulmus americana) so that infection could be studied. In surveys made in 1971, expression of external symptoms of Dutch elm disease was observed on elms which had been caged with beetles during the period May 26 to July 9, 1971. Vascular discoloration (internal symptom expression), fungus spread, fungus contamination of beetles, and transmission of fungus to the host by beetles were pronounced on elms caged with beetles from June 3 to July 2.Ceratocystis ulmiwas recovered from leaves of trees caged during the period May 26 to July 2. Until May 31, 1972, dieback and death resulting from infection were restricted to trees caged with beetles during June. Corresponding development of vascular discoloration and fungus spread in the host also occurred, mostly during the caging period in June. There was no appreciable change in beetle activity in xylem tissue during the period of experiment. These results suggest that the period of highest susceptibility of white elm to Dutch elm disease in 1971 in central Ontario was June 3 to July 2.Inoculation through feeding by caged beetles carryingC. ulmiis probably the method that most closely approximates natural infection.

ISSN:0008-4026    

DOI:10.1139/b79-047

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

The ultrastructure of healthy and clover yellow mosaic virus (CYMV) infected leaves of White Dutch clover has been examined in an electron microscope using both thin-section and freeze-fracture techniques. A striking difference between leaves from healthy and diseased plants was that more starch grains were present in infected leaves compared with healthy ones. Feeding 3′,5′-cyclic adenosine monophosphate (cAMP) or dibutyryl-cAMP (bt-cAMP) to both healthy and diseased plants induced rapid dissociation of accumulated starch grains. Examination of freeze-fracture replicas indicated that this dissociation is associated with alterations in the ultrastructure of chloroplast and cell membranes. These alterations include aggregation of intramembranous particles and blebbing and wrinkling of the membranes. The significance of these alterations in relation to the dissociation of starch grains in CYMV-diseased leaves is discussed.

ISSN:0008-4026    

DOI:10.1139/b79-048

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

PseudocenangiumKarst. is redescribed and illustrated, andSiroscyphellaHöhn. is reduced to synonymy with it. Two species,P. pinastriandP. succinenm, are accepted.SeptopatellaPetrak, based onP. septatum, is confirmed as a distinct form genus.Pseudocenangium hartigianumandP. umenseare made the types of the new form generaGelatinopycnisandPocillopycnisrespectively.Pseudocenangium laricinumis excluded. The related form genusLinodochium hyalinum(Lib.) Höhn. is redescribed and illustrated.

ISSN:0008-4026    

DOI:10.1139/b79-049

出版商:NRC Research Press    

年代:1979

数据来源: NRC

摘要:

Barley styles were examined with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) before and after pollination. Pollen tube penetration of a stigmatic hair may follow initial missing of the hair and (or) a period of growth on the hair surface. Changes in hair cell walls occur at penetration sites. Absence of demonstrable reserve carbohydrate in hair cells and styles and its abundance in pollen tubes suggest that early tube growth is largely dependent on endogenous substrates relative to its carbohydrate requirement. The pollen tube wall has an inner, somewhat reticular region and an outer, multilayered fibrillar region. Membrane-bound pollen tube vesicles containing reticular material fuse with the pollen tube membrane, contributing to development of the pollen tube wall. Vesicles and tube wall are stained by Ruthenium Red; this staining is compared with results of periodic acid–silver proteinate treatment. Two types of tube growth anomalies are reported. In the first, a tube may grow out of a hair and discharge its cytoplasm onto the hair surface through an aperture. Discharged, naked tube cytoplasm often remains appressed to hair surfaces. In the second, a tube may grow into a hair cell and discharge its contents therein through an apparently similar aperture. Vegetative nuclei appear unaltered during early pollen tube growth, but there are minor structural alterations in sperms and vegetative cell cytoplasm.

ISSN:0008-4026    

DOI:10.1139/b79-050

出版商:NRC Research Press    

年代:1979

数据来源: NRC