PubMed Health⌕ Search

Biomedical subjects

E R Allen

Publications and source records attributed to E R Allen.

At least 19 recordsLinked to original sources
PubMed1997

Overexpression of glutathione S-transferase/glutathione peroxidase enhances the growth of transgenic tobacco seedlings during stress.

Transgenic tobacco seedlings that overexpress a cDNA encoding an enzyme with both glutathione S-transferase (GST) and glutathione peroxidase (GPX) activity had GST- and GPX-specific activities approximately twofold higher than wild-type seedlings. These GST/GPX overexpressing seedlings grew significantly faster than control seedlings when exposed to chilling or salt stress. During chilling stress, levels of oxidized glutathione (GSSG) were significantly higher in transgenic seedlings than in wild-types. Growth of wild-type seedlings was accelerated by treatment with GSSG, while treatment with reduced glutathione or other sulfhydryl-reducing agents inhibited growth. Therefore, overexpression of GST/GPX can stimulate seedling growth under chilling and salt stress, and this effect could be caused by oxidation of the glutathione pool.

Agriculture↗
PubMed1995

Dome epithelium and follicle-associated basal lamina pores in the avian bursa of Fabricius.

BACKGROUND: The immunological role played by the avian bursa of Fabricius has been well established. Although numerous studies have also reported on the development and general morphology of this organ, some structure-function relationships still have not been fully explained. METHODS: Bursae from chickens at three developmental stages were removed and examined by scanning electron microscopy. Routine preparation was used as well as sonication (microdissection). Micrographs were used for qualitative morphological study and for quantitative morphometric analyses. RESULTS: Routine SEM observations were similar to those previously reported in the literature. Sonicated specimens allowed topographical study of various levels of surface erosion. Two types of surface cells were observed: typical absorptive epithelium and follicle-associated epithelial (FAE) cells. Erosion of the dome surface epithelium revealed basal lamina pores in the region over the subepithelial lymphoid follicles. These pores were present at hatching. Morphometric analysis of dome and pore areas revealed that the pore area decreases in relation to dome area with aging. CONCLUSIONS: Basal lamina pores may provide a communication route between the lymphoid follicles and the external environment via the FAE cells. Also, the close association between the FAE cells of the epithelial domes, the epithelial pores, the capillary complex of the previously described bursal--blood barrier, and the subepithelial lymphoid follicles could represent a morphological "pore complex" that matures early in posthatching development and may be related to the immunological function of the bursa.

Aging↗
PubMed1994

Biofiltration control of hydrogen sulfide. 2. Kinetics, biofilter performance, and maintenance.

The kinetics of H2S oxidation in a biofilter were evaluated and the reaction rates determined to be first-order at low concentrations (< 200 ppm), zero-order at high concentrations (> 400 ppm), and fractional-order in the intermediate concentration range for H2S in the inlet waste gas. The overall performance of the biofilter system and changes in compost properties were investigated for 200 days of operation. The compost biofilter showed good buffering capacities to variations in gas flow rate and pollutant (H2S) loading impacts. Hydrogen sulfide removal efficiencies exceeding 99.9% were consistently observed. System acidification and sulfate accumulation were identified as inhibitors of required biological activity. Routine washing of the compost effectively mitigated these deficiencies. System upset was determined to be caused by compost dry-out or system overloading. Methods were developed to provide for recovery of contaminated filter material.

Air Pollutants↗
PubMed1991

Lunar outpost agriculture.

America's long-term commitment to a new Space Exploration Initiative has focused attention on the basic requirements for establishing a permanently manned lunar outpost and, ultimately, a martian one. High among these is the development of Regenerative Life Support Systems--with lunar agriculture an essential component--to provide a high level of self-sufficiency.

Agriculture↗
PubMed1988

Genetic mapping and physiological consequences of metE mutations of Bacillus subtilis.

Three metE mutations of Bacillus subtilis, which cause cells to have a 25- to 200-fold decrease in L-methionine S-adenosyltransferase (EC 2.5.1.6) activity, were mapped between bioB and thr. The corresponding three metE mutants contained three- to fourfold less intracellular S-adenosylmethionine (SAM) but at least sevenfold more methionine than the metE+ strain when grown in synthetic medium. This indicates a strong feedback control of SAM on its synthesis. However, only the metE2 strain, with the lowest SAM concentration, grew at a slightly lower rate than the parent, which showed that an intracellular concentration of about 25 microM SAM was critical for growth at the normal rate. Neither DNA methylation (measured by bacteriophage luminal diameter 105 restriction) nor sporulation was affected at this low SAM concentration. Addition of methionine to the growth medium caused an increase in the pool of SAM in some but not all metE mutants. Coaddition of adenine did not change this result. However, the extent of sporulation (induced by mycophenolic acid) was decreased 50-fold in all mutants by the addition of methionine and adenine. Therefore, the combination of methionine and adenine suppresses sporulation regardless of whether it causes an increase in the level of SAM.

Adenine↗
PubMed1986

An ethA mutation in Bacillus subtilis 168 permits induction of sporulation by ethionine and increases DNA modification of bacteriophage phi 105.

In contrast to Escherichia coli and Salmonella typhimurium, Bacillus subtilis could convert ethionine to S-adenosylethionine (SAE), as can Saccharomyces cerevisiae. This conversion was essential for growth inhibition by ethionine because metE mutants which were deficient in S-adenosylmethionine synthetase activity, were resistant to 10 mM ethionine and converted only a small amount of ethionine to SAE. Another mutation (ethA1) produced partial resistance to ethionine (2 mM) and enabled continual sporulation in glucose medium containing 4 mM DL-ethionine. This sporulation induction probably resulted from the effect of SAE, since it was abolished by the addition of a metE1 mutation. The induction of sporulation was not simply controlled by the ratio of SAE to S-adenosylmethionine, but apparently depended on another effect of the ethA1 mutation, which could be demonstrated by comparing the restriction of clear plaque mutants of bacteriophage phi 105 grown in an ethA1 strain with the restriction of those grown in the standard strain. The phages grown in the ethA1 strain showed increased protection against BsuR restriction. We propose that SAE induces sporulation through the inhibition of a key methylation reaction.

Adenosine↗
PubMed1986

A delay in the appearance of myosin in dystrophic chicken embryos.

Growth patterns during myogenesis were observed in vitro using normal and dystrophic New Hampshire Red chick embryos. The pectoral muscles from 6 d old embryos were removed, dissociated and grown in culture. Smaller muscle straps, both in size and number, as well as pseudostraps were seen in cultures from the myopathic embryos. There was a 1 1/2 d delay in the appearance of thick myosin-like myofilaments as well as large polyribosomes actively synthesizing myosin in the dystrophic muscle cells. Myosin may be a necessary constituent during myogenesis for the occurrence of normal fusion and thus myotubes.

Animals↗
PubMed1985

Evidence for a blood-bursa barrier.

By use of horseradish peroxidase (Sigma Type II) as a vascular tracer the competence of the bursal microvasculature was evaluated in 15-day-old chicks. Within 5 min circulation time tracer could be identified only within the vascular tree with no leakage into the perivascular or extracellular spaces. After 10 min circulation time tracer was no longer present in the bursal vessels. Since no tracer was ever identified among the parenchymal elements of the organ these data suggest that a blood-organ (blood-bursa) barrier may exist similar to that found in thymus and brain.

Animals↗
PubMed1985

Recovery from energy deficit in golden hamsters.

Hamsters feeding at greater than 2-h intermeal intervals (IMI) lose weight but recover from weight losses without hyperphagia if they are allowed to feed at 2-h IMIs (Am. J. Physiol. 236 (Endocrinol. Metab. Gastrointest. Physiol. 5): E105-E112, 1979). To determine the relative importance of changes in energy expenditure and fat synthesis in their energy regulation, measurements were made of resting metabolic rate, respiration by brown adipose tissue (BAT), locomotion, fecal energy content, and insulin and hepatic lipogenic enzyme responses to feeding in underweight hamsters allowed to feed at 2- or 5-h IMIs. Energy deficit suppressed the resting metabolic rate and general locomotor activity and increased the activity of fatty acid synthetase (FAS). Heat production by BAT increased in underweight hamsters. Increase in IMIs blocked the postprandial insulin release, reduced plasma insulin concentration and FAS activity, and increased malic enzyme activity. Thus ad libitum feeding hamsters recover from energy deficit by reducing energy expenditure, whereas failure to add additional meals and impaired insulin and changed lipogenic responses to feeding produce energy deficits in infrequently feeding hamsters.

Adipose Tissue, Brown↗
PubMed1984

The musculus complexus of normal and dystrophic chicken embryos.

Abnormalities have previously been reported in the pectoral muscle of embryos and young chicks from a pure strain of New Hampshire Red chickens homozygous for inherited muscular dystrophy. Fine structural studies of the musculus complexus in normal and dystrophic embryos were undertaken because of a sharp decrease in hatching by the diseased birds. Ultrastructural differences found between the normal and dystrophic embryos included a leached sarcoplasm, swollen and distorted mitochondria and tubular components, a lack of polyribosomes (myosin synthesis), and the formation of pseudostraps during differentiation of the myopathic hatching muscle. These differences may curtail differentiation until a point after the critical hatching time.

Animals↗
PubMed1983

A model to study local effects of thermal trauma on muscle metabolism.

To study local effects of burn on muscle in the absence of direct tissue damage, a rat's foot was insulated and one hindlimb was scalded by immersion in 85 degrees C water for 3 sec. Upon recovery, rats exhibited normal locomotion with both hindlimbs in spite of a full-thickness burn from ankle to knee. Thus the effects of the burn were not complicated by disuse atrophy. As in human burns, histological examination of soleus from the burned leg showed it to be morphologically indistinguishable from normal tissue. After 2 or 4 days postburn, the rat was sacrificed and the soleus muscles from the burned and unburned leg were incubated in vitro to measure protein turnover. Muscle from the burned leg demonstrated a maximal increase in protein breakdown 2 days postburn with no change in protein synthesis. At 4 days postburn, protein breakdown remained elevated and synthesis remained unchanged. Since metabolism of contralateral (unburned) muscle was identical to muscle from unburned animals, burn-induced changes must be ascribed to local and not to systemic mediators. Therefore, these experiments demonstrate that local mediators of burn-induced muscle catabolism primarily augment protein breakdown.

Animals↗
PubMed1981

An analysis of the integrity of the brachial motor unit in the dystrophic chick embryo.

In New Hampshire chickens, the primary clinical symptom of dystrophy is limitation of wing motility. Examination of the brachial-level motor unit in chick embryos homozygous for dystrophy reveals abnormalities in both muscular and neural components. Wing motility in these embryos is abnormal as early as six days, and there is a corresponding lack of differentiation of the pectoralis major muscle. The findings suggest that delayed development of brachial-level neuronal pathways is responsible for the decreased wing motility and early degeneration of the pectoral muscle.

Animals↗
PubMed1981

Sarcomere formation in dystrophic skeletal muscle.

Early aspects of in vivo sarcomere organization were studied using normal and dystrophic New Hampshire chick embryos. Brachial somites 17-22 were removed from stages 16 through 28 embryos, processed for electron microscopy, and analyzed. Comparisons of normal and dystrophic material disclosed that thick filaments appeared later in dystrophic myotomal cells. This was correlated with a similar delay in the appearance of long polyribosomes. By stage 28, normal myotomal cells contained well-defined sarcomeres, whereas dystrophic sarcomeres were frequently unorganized, with myofilaments in poor longitudinal alignment. Periodic tubules were poorly developed or lacking.

Animals↗
PubMed1979

Early detection of inherited muscular dystrophy in chickens.

New Hampshire chickens, homozygous for inherited muscular dystrophy, display clinical manifestations at an early age. A fine structural examination of embryos from this strain shows marked degenerative changes four days prior to hatching. The Z bands appear to dissolve progressively to the point where finally the myofibrils become uniformly dense with no detectable banding patterns.

Animals↗
PubMed1979

Aspects of normal and dystrophic chicken muscle grown in vitro.

Pectoral muscle from normal and dystrophic New Hampshire chicken embryos was dissociated and grown in vitro. Marked differences between the two types of cell cultures were observed with the light and electron microscopes during early myogenic stages. The diseased myoblasts assumed a polarized affect and fused into smaller and fewer myotubes. Pseudostraps rather than true muscle straps were often seen in diseased cultures. There was also a delay in the appearance of myosin containing thick myofilaments in differentiating dystrophic muscle cells.

Animals↗
PubMed1978

Sarcotubular development in dystrophic skeletal muscle cells.

Dilations of the sarcotubular system and misaligned myofilaments have been reported as early indicators of muscular dystrophy in skeletal muscle. Since the developing tubular component is believed instrumental in initial myofilament alignment during myogenesis, tubular development is evaluated using normal and dystrophic chick embryo skeletal muscle and cultures of normal and dystrophic embryonic pectoral muscle incubated in the presence of horse spleen ferritin. Comparisons of the findings show that periodic tubules are absent from dystrophic somitic muscle and that invaginating tubules from the sarcolemma are found in fewer, randomly located areas of dystrophic pectoral muscle cells. The results indicate that the tubular component is not involved in the bizarre vesiculations seen in mature dystrophic muscle, however, the malalignment of dystrophic myofilaments is probably the result of the poorer development of the T system in this muscle.

Animals↗
PubMed1978

Ultrastructural, cyto- and biochemical observations during turnover of plasma membrane in duck salt gland.

The mechanism of plasma membrane turnover was investigated using the duckling salt gland as a model system. Feeding fresh water to salt-stressed ducklings results in a decrease in the Na, K-ATPase in salt gland to non-stressed levels in about 7 days, as measured by ATP hydrolysis and 3H-ouabain binding. Electron micrographs reveal that this is accompanied by a decrease in plasma membrane infoldings on the basal and lateral borders of gland secretory cells. Simultaneously there is an increase in filamentous material and a rise in acid phosphatase and peptidase activities in these cells. Cytochemistry shows that the acid phosphatase activity is mostly associated with the basal or basolateral regions of secretory cells. These ovservations could indicate that the removal of plasma membrane components is accomplished by internalization and digestion within the secretory cells.

Acid Phosphatase↗