- Saint Paul, United States
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Microbiology, Mycology, Molecular Biology, Plant Biology, Biology, and 15 moreScanning Electron Microscopy, Modulation, Gene expression, Pathophysiology, Peroxidase, Cell Death, Genetic determinism, Gene, Hordeum vulgare, Gen, Peroxidases, Gramineae, Powdery Mildew, Plant Pathology, and Phenylalanine ammonia lyase
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Barley, oat and wheat were used as both inappropriate hosts (IH) and appropriate hosts (AH) for three formae speciales of the fungus Blumeria graminis, the causal agent of powdery mildew disease. Treatment with either the glucose analog... more
Barley, oat and wheat were used as both inappropriate hosts (IH) and appropriate hosts (AH) for three formae speciales of the fungus Blumeria graminis, the causal agent of powdery mildew disease. Treatment with either the glucose analog 2-deoxy- D -glucose (DDG) or with D -mannose dramatically suppressed penetration resistance in IH and to a much lesser extent in AH combinations.
Research Interests:
Research Interests:
Research Interests:
Research Interests: Plant Biology, Biology, Medicine, Western blotting, Genetic Engineering, and 15 moreTriticum Aestivum, Plant diseases, Fusarium, Fusarium Graminearum, Resistance, Statistical Significance, Disease Severity, Gene, Gen, Gramineae, Deoxynivalenol, Large Scale, Triticum, Thallophyta, and reverse transcriptase polymerase chain reaction
Research Interests:
Research Interests:
Research Interests:
... The Green Revolution was a mid-20th century decades-long international science and educational effort to ... that exploited it, and the concept of the Land Grant University and its role. ... project represents the culmination of close... more
... The Green Revolution was a mid-20th century decades-long international science and educational effort to ... that exploited it, and the concept of the Land Grant University and its role. ... project represents the culmination of close to 100 years of collaborationscientific and archival ...
Research Interests:
Page 1. Canadian Journal of Plant Pathology Revue canadienne de Phytopathologie Published by Publiée par The Canadian Phytopathologien! Society La Société Canadienne de Phytopathologie Volume 20(2):137-220 June ...
Research Interests:
Papillae were deposited in barley epidermal cells directly beneath appressoria of Erysiphe graminis f. sp. hordei and appeared as hemispherical, internal wall appositions. The papilla response began shortly after the formation of a... more
Papillae were deposited in barley epidermal cells directly beneath appressoria of Erysiphe graminis f. sp. hordei and appeared as hemispherical, internal wall appositions. The papilla response began shortly after the formation of a rapidly moving cytoplasmic aggregate beneath the appressorium. As documented in coleoptile tissue by time-lapse light microcinematography, the papillae grew rapidly for 20–30 min after becoming visible, their radii increasing by 0.1 μm/min. For small papillae, deposition continued for about 30 min; for larger papillae, deposition continued for 120–180 min. Results with transmission electron microscopy on leaf epidermal cells suggested that papilla deposition by host cytoplasmic aggregates can be divided into four sequential stages: (i) the deposition of osmiophilic (lipidic) materials, (ii) the deposition and partial compaction of nonosmiophilic, amorphous material (probably insoluble polysaccharides), (iii) compaction of nonosmiophilic, amorphous materia...
Research Interests:
Cytoplasmic aggregates that formed in susceptible barley epidermal cells 11-12 h after inoculation with Erysiphe graminis were examined by light microscopy in living specimens and by electron microscopy in fixed specimens. Rapid... more
Cytoplasmic aggregates that formed in susceptible barley epidermal cells 11-12 h after inoculation with Erysiphe graminis were examined by light microscopy in living specimens and by electron microscopy in fixed specimens. Rapid development of the aggregate (5–10 min) suggested that cytoplasm migrated to the site of each aggregation. The aggregate contained features generally associated with areas of high metabolic and synthetic activity: abundant mitochondria, rough endoplasmic reticulum (associated with smooth cisternae), Golgi bodies, and polyribosomes. Leucoplasts and nuclei were sometimes near aggregates but not consistently. Microbodies and osmiophilic spherosomes were not present.
Research Interests:
Fifteen monocotyledonous species were separately inoculated with spores of Erysiphe graminis f. sp. hordei (a parasite of barley) and E. cichoracearum (a parasite of cucurbits) to learn cytologically what types of parasite failures and... more
Fifteen monocotyledonous species were separately inoculated with spores of Erysiphe graminis f. sp. hordei (a parasite of barley) and E. cichoracearum (a parasite of cucurbits) to learn cytologically what types of parasite failures and host-cell responses protect nonhosts from disease. Tissues were stained with acid fuchsin and aniline blue, 24 and 72 h after inoculation, and examined microscopically. For each combination of higher plant species and fungus, fungal development and host responses were recorded for 2022–4679 spores and 15–2206 germlings, using a binary pathway system to tabulate and statistically analyze results.Nonhosts showed a battery of defenses, each of which could stop a large part of an attacking powdery mildew population. These defenses were expressed sequentially during fungal differentiation, leading to a progressive attrition in the number of germlings able to continue. The defenses were expressed on or in the following host structures: (i) the leaf surface,...
Research Interests:
The oat blue dwarf virus is a small spherical virus (28–30 nm) in diameter and is obligatorily transmitted by the aster leafhopper Macrosteles fascifrons Stål. The virus causes abnormalities in the phloem development of infected plants.... more
The oat blue dwarf virus is a small spherical virus (28–30 nm) in diameter and is obligatorily transmitted by the aster leafhopper Macrosteles fascifrons Stål. The virus causes abnormalities in the phloem development of infected plants. Hyperplasia and limited hypertrophy of phloic procambium, in a given procambial strand, begin only after the maturation of the first protophloem sieve-tube element in that particular localized area. The majority of phloem elements produced in hyperplastic areas are parenchymatous, have truncated end walls, and lack sieve plates. Electron-microscopic observations substantiated the hypothesis that the virus was phloem-limited by revealing virus particles only in phloem elements. The greatest accumulation of virus particles was observed in the region between immature and fully vacuolated phloem elements, implicating virus synthesis in immature elements. Crystals of virus particles were often large enough to be seen by light microscopy.
Research Interests:
Three specimen preparation procedures were used in conjunction with scanning electron microscopy and energy dispersive X-ray microanalysis to determine, by comparison among preparation methods, both soluble and insoluble elements at... more
Three specimen preparation procedures were used in conjunction with scanning electron microscopy and energy dispersive X-ray microanalysis to determine, by comparison among preparation methods, both soluble and insoluble elements at Erysiphe graminis – barley leaf epidermal cell encounter site areas where attempted fungal penetration by appressoria failed. Near isogenic lines (RISO 5678-R and RISO 5678-S) of barley differing by mutation at the Ml-o locus were used. The recessive ml-o allele conditions barley epidermal cells to respond with papilla-associated resistance to E. graminis, while the dominant Ml-o allele allows for successful penetration of the majority of E. graminis germlings. Frozen-hydrated and freeze-dried specimens maintained soluble and insoluble elements, while specimens fixed by formalin – acetic acid – alcohol and critical point dried lost soluble elements. The effects of specimen preparation on electron-beam penetration and depth of X-ray excitation were calcul...
Research Interests:
Events in development of powdery mildew fungi from spore germination to formation of the first haustorium and hypha, including host cell responses, were cataloged using a binary pathway system. This system branches at... more
Events in development of powdery mildew fungi from spore germination to formation of the first haustorium and hypha, including host cell responses, were cataloged using a binary pathway system. This system branches at "event-points" which represent sites of "on–off" alternatives for the occurrence of an event or sites where one of two alternative events occur. The system permits statistical comparisons of probabilities for different events within a given host–parasite combination and for specific events in different host–parasite combinations. Data from the binary pathway system can be converted to percentage of total spores to show the size of the fungal population which passes each event-point, or the data can be resorted to determine how many germlings are associated with a given combination of events.The binary system was used with data for powdery mildew of barley obtained from whole leaves harvested 1 and 2 days after inoculation, which were fixed and then ...
Research Interests:
Within minutes of spore deposition, enzymes including cutinase are released by conidia of Erysiphe graminis; these may prepare the infection court and facilitate subsequent fungal development. Germination follows with emergence of the... more
Within minutes of spore deposition, enzymes including cutinase are released by conidia of Erysiphe graminis; these may prepare the infection court and facilitate subsequent fungal development. Germination follows with emergence of the primary germ tube, which contacts the host leaf. Extracellular material is secreted beneath the primary germ tube, which adheres to the leaf. The primary germ tube forms a penetration peg that breaches the host surface and gains access to host cell components including water. The primary germ tube also recognises factor(s) present in the host surface, and this stimulates elongation of the second-formed germ tube. The elongated second tube in turn responds to host surface factor(s) by differentiating an appressorium. Extracellular material, secreted beneath the growing appressorial germ tube, is laid down thickly around the appressorial lobe. An inner ring of extracellular material can often be seen surrounding penetration pores revealed by the removal ...
Research Interests:
During the past 1 5 years there has been an explosion of technological innovation that has provided a variety of powerful commercial instruments and techniques for use in the biological sciences. The information gained from use of these... more
During the past 1 5 years there has been an explosion of technological innovation that has provided a variety of powerful commercial instruments and techniques for use in the biological sciences. The information gained from use of these instruments and techniques is leading to a revolution in biology. One of the areas in which technological innovation has made great advances is in the area of microanalysis. Microanalysis refers to chemical analysis of very small quantities of substances, usually requiring specialized instrumentation or use of very small scale apparatus. In the biological sciences the two most commonly used, but not mutually exclusive, approaches to microanalysis are (a) in vitro procedures of tissue fractionation, separation, and identification, fol lowed by many types of analytical techniques (chromatography, electro phoresis, mass spectroscopy, etc), and (b) in situ procedures where chemical analysis is accomplished within intact cells and tissues by a variety of methods and linked to the use of various types of microscopy. Many types of histochemical and cytochemical methods can, by definition, be included as microanalysis procedures. In recent years, however, the term microana lysis has become closely identified with x-ray microanalysis, or with a variety of other techniques like Auger electron analysis, cathodolumines cence, ion scattering spectrometry, secondary ion mass spectrometry, x-ray
Research Interests:
Occurrences of mycoplasma-like organisms (MLO) and viruses or virus-like particles in both plants and insects have been reported and have been studied mainly by the use of electron microscopy. Several examples of these dual infections are... more
Occurrences of mycoplasma-like organisms (MLO) and viruses or virus-like particles in both plants and insects have been reported and have been studied mainly by the use of electron microscopy. Several examples of these dual infections are listed in TABLE 1 . In some cases only observations have been made, and the exact identity of either or both agents remains unknown. Undoubtedly many additional cases of dual infections of both plants and insects by MLOs and viruses will be reported. To date, at least 40 plant diseases have suspected MLO etiol~ g y . ~ ~ , ~ ~ An example, in the plant kingdom, of the numerous possibilities for mixed infections can be shown by looking at the aster yellows disease. Aster yellows disease has been attributed to an MLO and has a host range of about 300 plant species,2o many of which are hosts for one or more viruses, so there are many possibilities for mixed infections.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Decomposing terrestrial leaf litter plays a primary role in the carbon and nutrient budgets of many lake ecosystems (Gasith and Hasler 1976); disruption of that role impairs ecosystem integrity. Release of nutrients from litter into lake... more
Decomposing terrestrial leaf litter plays a primary role in the carbon and nutrient budgets of many lake ecosystems (Gasith and Hasler 1976); disruption of that role impairs ecosystem integrity. Release of nutrients from litter into lake ecosystems is primarily mediated by the microbial community (Buttimore et al. 1984). Microbes accumulate nutrients from litter, sediments, and the water column, concentrating elements and making them available to higher trophic levels. Ecosystem stresses such as lake acidification alter microbial ...
Research Interests:
Research Interests:
Rates of haustorium formation by Erysiphe graminis f.sp. hordei were determined for epidermal tissues of primary leaves of a near-isogenic pair of barley (Hordeum vulgare) lines, AlgR and AlgS, which differed at the Mla locus for... more
Rates of haustorium formation by Erysiphe graminis f.sp. hordei were determined for epidermal tissues of primary leaves of a near-isogenic pair of barley (Hordeum vulgare) lines, AlgR and AlgS, which differed at the Mla locus for compatibility with the fungus. Epidermal cells were divided into two classes, namely shorter or longer than 450 μm. Cells near stomatal files were always short, whereas cells more distant from stomata were long on the abaxial surface, long on the adaxial surface over vascular bundles, but short on the adaxial surface when not over vascular bundles. At 24 h after inoculation, haustoria were formed in 70–80% of attacked short cells but in only 15–20% of attacked long cells. When haustoria were absent, papillae were present, so papilla-associated resistance was more frequent in long than in short cells. However, the percentage of attacked sites with papillae was the same in AlgR and AlgS, indicating that papilla-associated resistance was not related to Mla inc...
Research Interests:
Numerous plant pathological investigations have been published where pathologists determined elemental differences between diseased and healthy plant tissue using unfractured bulk specimens and energy dispersive x-ray microanalysis (EDX).... more
Numerous plant pathological investigations have been published where pathologists determined elemental differences between diseased and healthy plant tissue using unfractured bulk specimens and energy dispersive x-ray microanalysis (EDX). In these studies effects of specimen preparation procedures were largely ignored (1). Our objective was to compare bulk specimen preparation procedures using healthy leaf epidermal (surface) cells of barley, Hordeum vulgare, (Fig. 1) to determine advantages and disadvantages of each procedure for reference to future pathological work using EDX. Three preparation procedures were compared: 1) Frozen-hydrated (FH) specimens to maintain soluble and insoluble elements in situ; 2) Freeze-dried (FD) specimens to maintain total soluble and insoluble elements and allow deeper beam penetration than does FH, and; 3) Formalin/acetic acid/ethanol (FAA) fixed specimens, dehydrated in ethanol, and critical point dried (CD) using CO2, for determination of elementa...
Research Interests:
Research Interests:
Research Interests:
ABSTRACT Conidia of Erysiphe graminis DC f.sp. avenae ex. Merat were applied at various densities (low = approximately 30 mm−2, medium = approximately 100 mm−2, high = approximately 300–400 mm−2) to first leaves of spring oat (Avena... more
ABSTRACT Conidia of Erysiphe graminis DC f.sp. avenae ex. Merat were applied at various densities (low = approximately 30 mm−2, medium = approximately 100 mm−2, high = approximately 300–400 mm−2) to first leaves of spring oat (Avena sativa) cvs Selma and Maldwyn. As previously published, high inoculum density results in activated (enhanced) host cell defence to fungal penetration, and this correlates with elevation in the frequency and intensity of host cell autofluorescent responses. In the current study, leaves were infused with either water (control treatment) or the phenylalanine ammonia lyase (PAL) inhibitors α-aminooxy-β-phenylpropionic acid (AOPP) or α-aminooxy acetic acid (AOA) at concentrations known to be inhibitory to PAL from oats. Results confirm and extend previous observations showing that these PAL inhibitors suppress localized autofluorescent host cell responses to fungal germ tube contact and increase susceptibility to penetration (haustorium formation) from appressoria. The PAL inhibitors, particularly AOPP, suppressed activated defence due to inoculum density and decreased the frequency and intensity of host cell autofluorescence responses. The data support the hypotheses that the activated defence is related to autofluorogenic host responses, and that the autofluorogens are phenolic compounds. Involvement of phenolic compound metabolism in activated defence was shown by assays of the specific activity of PAL from control cv. Selma leaves inoculated with low and high densities of conidia. Compared to uninoculated controls, the specific activity of PAL was enhanced at 6 h after inoculation (when responses to the primary germ tubes of E. graminis were evident), but there was little difference between low and high density inoculations at this time. At 18 h after inoculation (when responses to fungal appressoria were evident), the specific activity of PAL was substantially greater from high than from low inoculum density inoculations. In a coincidental observation, brown colouration (suggesting phenol oxidation) visible in many epidermal cell papillae associated with appressorial attack in control leaves, was not present in most papillae from AOPP-treated leaves.
Research Interests:
Research Interests:
Research Interests:
ABSTRACT Hypersensitive cell death (HR) of adaxial leaf epidermal cells of barley containing the M1a gene for resistance to powdery mildew germlings, Erysiphe graminis f. sp. hordei, was investigated for temporal relations between cell... more
ABSTRACT Hypersensitive cell death (HR) of adaxial leaf epidermal cells of barley containing the M1a gene for resistance to powdery mildew germlings, Erysiphe graminis f. sp. hordei, was investigated for temporal relations between cell death, onset of autofluorescence, and accumulation of insoluble silicon (Si). Physiological cell viability or death of barley epidermal cells was determined by concomitant uptake of the vital dye neutral red, and by cell plasmolysis using alpha methyl-d-glucose. Cell death, as judged by lack of neutral red uptake and lack of plasmolysis, first occurred in a low percentage of attacked epidermal cells at 15 h after inoculation and increased to a maximum of 72% at 21 and 24 h. Cells judged dead by physiological criteria always exhibited whole-cell autofluoresence by blue light excitation. Autofluorescence was weak in dying and recently dead cells, but it increased in intensity with time following cell death. It was concluded that autofluorescence accompanies cell death and is perhaps due to release of phenolic compounds from cell vacuoles after cell membranes have lost their semipermeable properties. Insoluble Si accumulation, as determined by energy dispersive X-ray microanalysis using a scanning electron microscope, did not directly correspond to the initial appearance of autofluorescence in HR-dead cells, but occurred gradually after death and in apparent relation to increasing autofluorescence intensity. An hypothesis is stated that phenolics are released by decompartmentalization following cell death and accumulate in the dead cell's wall area causing autofluorescence, and that these phenolics form insoluble complexes with Si moving apoplastically in epidermal wall areas due to passive, transpiration stream transport.
Research Interests:
... A Clarke, R Desikan, RD Hurst, JT Hancock and SJ Neill, NO way back: nitric oxide and programmed cell death in Arabidopsis ... YD Wei, E d Neegaard, H Thordal-Christensen, DB Collinge and V Smedegaard-Petersen, Accumulation of a... more
... A Clarke, R Desikan, RD Hurst, JT Hancock and SJ Neill, NO way back: nitric oxide and programmed cell death in Arabidopsis ... YD Wei, E d Neegaard, H Thordal-Christensen, DB Collinge and V Smedegaard-Petersen, Accumulation of a putative guanidine compound in relation ...
Research Interests:
Soybean mesophyll cells from stunted and chlorotic trifoliolate leaf tissue affected by bacterial (Pseudomonas glycinea Coerper) induced toxemia, had dense cytoplasm, little vacuolation, chloroplasts with few lamellae, and little starch... more
Soybean mesophyll cells from stunted and chlorotic trifoliolate leaf tissue affected by bacterial (Pseudomonas glycinea Coerper) induced toxemia, had dense cytoplasm, little vacuolation, chloroplasts with few lamellae, and little starch accumulation. Toxemia-affected cells exhibited no ultrastructural disruptions and resembled very young, healthy mesophyll cells. The main effect of the toxin appears to be a delay in mesophyll cell maturation rather than disruption at the ultrastructural level. Leaf mesophyll cells which had recovered from the bacterial toxemia appeared similar ultrastructurally to mature healthy cells, although they remained smaller.
Research Interests:
ABSTRACT Light microscopic details of interactions between Erysiphe graminis hordei and barley epidermal cells, in a genetically compatible host-pathogen combination, were observed using oblique bright field illumination in acetic... more
ABSTRACT Light microscopic details of interactions between Erysiphe graminis hordei and barley epidermal cells, in a genetically compatible host-pathogen combination, were observed using oblique bright field illumination in acetic acid-ethanol fixed leaves stained with Coomassie Brilliant Blue R-250. Host-pathogen contact sites were mapped and cytoplasmic detail photographed. Tissues were then critical point dried and contact sites examined under the light microscope were then examined in the scanning electron microscope (SEM). Insoluble silicon (Si) was located by energy dispersive X-ray microanalysis. Regardless of fungal success or failure Si was found in papillae and throughout the areas subtended by cytoplasmic aggregates. High levels of Si accumulated throughout certain dead epidermal cells characterized by dense staining cytoplasm. This sequential procedure allows, for the first time, direct correlations to be made between the X-ray microanalyses and the cytoplasmic details obtained by light microscopy. The procedure can be extended to link information gained by autofluor-escent reactions or other light microscopic procedures with SEM and X-ray microanalysis information.
Research Interests:
Typescript. Thesis (M.S.)--Mankato State University, 1966. Includes bibliographical references.
Thesis (Ph.D.)--University of Minnesota, 1970. Bibliography: leaves 62-64.