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Biomedical subjects

T J Cooke

Publications and source records attributed to T J Cooke.

At least 19 recordsLinked to original sources
PubMed2001

A cross-national comparison of the impact of family migration on women's employment status.

In this paper we consider the effects of family migration on women's employment status, using census microdata from Great Britain and the United States. We test a simple hypothesis that families tend to move long distances in favor of the male's career and that this can have a detrimental effect on women's employment status. Unlike many previous studies of this question, our work emphasizes the importance of identifying couples that have migrated together, rather than simply comparing long-distance (fe)male migrants with nonmigrant (fe)males individually. We demonstrate that women's employment status is harmed by family migration; the results we present are surprisingly consistent for Great Britain and the United States, despite differing economic situations and cultural norms regarding gender and migration. We also demonstrate that studies that fail to identify linked migrant couples are likely to underestimate the negative effects of family migration on women's employment status.

Adolescent↗
PubMed1999

Auxin metabolism in mosses and liverworts.

The plant hormone auxin (indole-3-acetic acid, IAA) is involved in the control of many phenomena during plant development. By characterizing steady-state free and conjugated IAA levels using a stable isotope dilution method coupled with gas chromatography- selected ion monitoring- mass spectrometry, this paper provides a detailed characterization of IAA metabolism in five liverworts, four mosses, and two tracheophytes. Long-term IAA conjugation patterns were monitored by incubating actively growing tissue with (14)C-IAA and then analyzing the de novo synthesis of IAA conjugates with radioimaging techniques. The liverworts, mosses, and tracheophytes can be differentiated by the total amount of IAA metabolites, the proportion of free and conjugated IAA, the chemical nature of their IAA conjugates, and the rates of IAA conjugation. Our tentative conclusion is that the liverworts appear to employ a biosynthesis-degradation strategy for the regulation of free IAA levels, in contrast to the conjugation-hydrolysis strategy apparently used by the mosses and tracheophytes. Such alternative metabolic strategies may have profound implications for macroevolutionary processes in these plant groups.

Journal Article↗
PubMed1998

A microtechnique for the analysis of free and conjugated indole-3-acetic acid in milligram amounts of plant tissue using a benchtop gas chromatograph-mass spectrometer.

A microtechnique was developed for the quantification of indole-3-acetic acid (IAA) in plant samples of one milligram fresh weight or less. The method permitted quantification of both free and conjugated IAA using a benchtop gas chromatograph-mass spectrometer. New methods for sample purification with high recovery at microscale levels, together with simple changes that result in enhanced sensitivity of the instrumentation, allowed for a significant reduction in the amount of plant material required for analysis. Single oat (Avena sativa L.) coleoptile tips could be studied with this method and were found to contain free and total IAA levels of 137 and 399 pg.mg-1 fresh weight, respectively. A single 5-d-old Arabidopsis thaliana (L.) Heynh. seedling was shown to contain 61 pg.mg-1 fresh weight free IAA and 7850 pg.mg-1 fresh weight of total IAA following basic hydrolysis. This microtechnique provides a way to accurately measure IAA levels in very small structures and individual seedlings, thus making it a valuable research tool for elucidating the role and distribution of auxin in relation to growth and development.

Arabidopsis↗
PubMed1998

Family migration and employment: the importance of migration history and gender.

"This article uses event history data to specify a model of employment returns to initial migration, onward migration, and return migration among newly married persons in the U.S. Husbands are more likely to be full-time employed than wives, and being a parent reduces the employment odds among married women. Employment returns to repeated migration differ by gender, with more husbands full-time employed after onward migration and more wives full-time employed after return migration events. We interpret these empirical findings in the context of family migration theory, segmented labor market theory, and gender-based responsibilities." Data are from the National Longitudinal Survey of Youth from 1979 to 1991.

Americas↗
PubMed1996

Family migration and the employment of married women and men.

"This research reconsiders the human capital hypothesis that married women have a lower probability of employment after family migration. The empirical analysis focuses on a sample of married parents in the economically active population residing in the midwestern United States in 1980. Our analysis establishes that, after controlling for the effects of migration self-selection bias, family migration increases the probability of employment among married women by 9 percent but has no effect on the probability of employment among married men. This research demonstrates the limitations of the human capital model of family migration and indicates the need for reconceptualizing family migration behavior."

Americas↗
PubMed1992

Regulation of indole-3-acetic Acid biosynthetic pathways in carrot cell cultures.

2,4-Dichlorophenoxyacetic acid (2,4-D) promotes the accumulation of tryptophan-derived indole-3-acetic acid (IAA) in carrot cell cultures during callus proliferation by a biosynthetic pathway that is apparently not active during somatic embryo formation. The effects of 2,4-D were examined by measuring the isotopic enrichment of IAA due to the incorporation of stable isotope-labeled precursors (deuterium oxide, [(15)N]indole, and (2)H(5)-l-tryptophan). Enrichment of IAA from deuterium oxide is similar in both cultured hypocotyls and cell suspension cultures in the presence and absence of 2,4-D, despite the large differences in absolute IAA concentrations. The enrichment of IAA due to the incorporation of [(15)N]indole is also similar in callus proliferating in the presence of 2,4-D and in embryos developing in the absence of 2,4-D. The incorporation of (2)H(5)-l-tryptophan into IAA, however, is at least 7-fold higher in carrot callus cultures proliferating in the presence of 2,4-D than in embryos developing in the absence of 2,4-D. Other experiments demonstrated that this differential incorporation of (2)H(5)-l-tryptophan into IAA does not result from differential tryptophan uptake or its subsequent compartmentation. Thus, it appears that differential pathways for IAA synthesis operate in callus cultures and in developing embryos, which may suggest that a relationship exists between the route of IAA biosynthesis and development.

Journal Article↗
PubMed1992

Comparison of Benzyl Adenine Metabolism in Two Petunia hybrida Lines Differing in Shoot Organogenesis.

The uptake and metabolism of the cytokinin benzyl adenine (BA) was compared in two lines of Petunia hybrida Vilm. differing in their shoot organogenic response. Leaf transfer experiments using shoot induction medium containing 4.4 micromolar BA showed that leaf explants from petunia line St40 required a shoot induction period of 6 to 10 days for commitment to shoot organogenesis; whereas leaf explants from petunia TLV1 required 12 to 28 days. The short induction period of petunia St40 and the higher organogenic response was positively associated with a threefold higher absorption of BA from the medium, an increased BA ribotide metabolite pool, the presence of BA within the explant during the shoot induction period, and the production of an unidentified metabolite C. However, the study of petunia TLV1 leaf explants showed that neither BA nor metabolite C are required during the shoot induction period for eventual shoot development. The longer shoot induction period of TLV1 was associated with low BA uptake during 24 days, a decreasing ribotide metabolite pool, the absence of benzyl adenosine triphosphate and metabolite C throughout the study, and the absence of BA within the explant during the shoot induction period. Differences in the shoot organogenic response of these related plant lines have been shown to be associated with differences in exogenous cytokinin uptake and the subsequent metabolism of that hormone.

Journal Article↗
PubMed1991

The structure of plasmodesmata as revealed by plasmolysis, detergent extraction, and protease digestion.

Plasmodesmata or intercellular bridges that connect plant cells are cylindrical channels approximately 40 nm in diameter. Running through the center of each is a dense rod, the desmotubule, that is connected to the endoplasmic reticulum of adjacent cells. Fern, Onoclea sensibilis, gametophytes were cut in half and the cut surfaces exposed to the detergent, Triton X 100, then fixed. Although the plasma membrane limiting the plasmodesma is solubilized partially or completely, the desmotubule remains intact. Alternatively, if the cut surface is exposed to papain, then fixed, the desmotubule disappears, but the plasma membrane limiting the plasmodesmata remains intact albeit swollen and irregular in profile. Gametophytes were plasmolyzed, and then fixed. As the cells retract from their cell walls they leave behind the plasmodesmata still inserted in the cell wall. They can break cleanly when the cell proper retracts or can pull away portions of the plasma membrane of the cell with them. Where the desmotubule remains intact, the plasmodesma retains its shape. These images and the results with detergents and proteases indicate that the desmotubule provides a cytoskeletal element for each plasmodesma, an element that not only stabilizes the whole structure, but also limits its size and porosity. It is likely to be composed in large part of protein. Suggestions are made as to why this structure has been selected for in evolution.

Cell Wall↗
PubMed1990

Infective arthritis secondary to bladder outflow obstruction.

We describe two cases of septic arthritis occurring in association with lower urinary tract infection in elderly men. In both cases the organism isolated from both the joint and the urine was Staphylococcus aureus. Further investigation of the urinary tract in both individuals identified bladder outflow obstruction secondary to benign prostatic hyperplasia predisposing them to infection. The urinary tract should be suspected as a focus of infection in septic arthritis in elderly men and further investigation of the urinary system may disclose a surgically correctable lesion.

Aged↗
PubMed1990

The distribution of plasmodesmata and its relationship to morphogenesis in fern gametophytes.

Fern (Onoclea sensibilis) gametophytes when grown in the dark form a linear file of cells (one-dimensional) called a protonema. In the light two-dimensional growth occurs which results in a heart-shaped prothallus one cell thick. The objective of this paper is to relate the most common pattern of cell division observed in developing gametophytes to the formation of the plasmodesmatal network. Since the prothalli are only two dimensional, we can easily determine from thin sections the total number and the density (number per unit surface area) of plasmodesmata at each developmental stage. As the prothallus grows the number of plasmodesmata increases 50-fold in the apical or meristematic cell. This number eventually reaches a plateau even though the density continues to increase with each new cell division. What is particularly striking is that both the number and density of plasmodesmata between adjacent cells is precisely determined. Furthermore, the pattern of plasmodesmata distribution is predictable so that (1) we can identify the apical meristematic cells by their plasmodesmata number, or density, as well as by their size, shape and location, (2) we can predict, again from plasmodesmata number, the location of a future wall of the apical cell prior to its actual formation, (3) we can show that the density of plasmodesmata in the triangular apical cell of the prothallus (14 plasmodesmata microns-2) is comparable to those reported for secretory glands which are known to have high rates of plasmodesmatal transport and (4) we can show that once the plasmodesmata have been formed during division, no subsequent change in the number of plasmodesmata occurs following cell plate formation.

Cell Division↗
PubMed1988

Modifications of extracellular electric and ionic gradients preceding the transition from tip growth to isodiametric expansion in the apical cell of the fern gametophyte.

Fern (Onoclea sensibilis L.) gametophytes exposed to blue light are induced to undergo a morphological transition from a tip-growing filament to a planar prothallus. Extracellular measurements of electric currents and localized ion activities around the apical cell of 8 to 10 day-old gametophytes were made with a vibrating probe and ion selective electrodes. In darkness, we observed exit current densities of an average of 75 nanoamperes per square centimeter near the tip and 2 to 15 nanoamperes per square centimeter along the lateral walls of this cell. Measurements with ion selective electrodes for H(+), K(+), and Ca(2+) showed that this cell was bounded by a thin layer of medium that was depleted in K(+) and Ca(2+) and exhibited a lower pH than the bulk solution. Both the K(+) and Ca(2+) depletion zones and the zone of higher acidity were particularly pronounced at the tip end of the cell; the pH at 2 micrometers from the tip was nearly 0.5 units more acid than the bulk medium at pH 6. Disruption of steady state, external gradients with media that contained lower concentrations of H(+), K(+), Ca(2+), or Cl(-) produced certain differences in the rates of restoration of particular ion zones, raising the possibility that some of the ion migrations are interdependent. Within 15 minutes after irradiation with blue light, current leaving the tip declined to levels which were indistinguishable from those leaving the lateral walls and there was a rapid lowering in the rates of tip acidification and K(+) depletion near the tip. The rapid dissipation of both the longitudinally aligned electrical field and the tip-localized asymmetries in external cation distribution in blue light suggest that loss of electrical polarity in this tip growing cell may be an initial step in the chain of events which govern changes in cell shape.

Journal Article↗
PubMed1987

Unusual patterns of somatic embryogenesis in the domesticated carrot: developmental effects of exogenous auxins and auxin transport inhibitors.

The effects of various exogenous auxins and polar auxin transport inhibitors on somatic embryogenesis in carrot cultures were investigated. Indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid do not disrupt the sequence or the polarity of individual stages in embryo development, but tend to cause developing embryos to revert to undifferentiated callus, with increasing frequency in later embryo stages. The transport inhibitors, N-(1-naphthyl)phthalamic acid and 2,3,5-triiodobenzoic acid, block morphological transitions to the subsequent stage; for example, they cause the formation of enlarged globular and oblong embryos. Heart embryos in these treatments usually develop additional lateral growth axes. These results shed light on the role of auxin and its polar transport in somatic embryogenesis.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1986

The role of electrical phenomena in tip growth, with special reference to the developmental plasticity of filamentous fern gametophytes.

Cell expansion in many plant structures, including algal rhizoids, fungal hyphae, root hairs, and pollen tubes, is restricted to their apical tips. Endogenous electric fields are seen to accompany polarized growth in all tip-growing cells studied to date. The extensive studies on absorptive tip-growing structures have established that positive currents enter their elongating tips, with a portion of the entry current being carried by a localized calcium influx into the extreme tip. The resulting tip-to-base gradient in calcium concentration appears to be responsible for maintaining polarized growth in these systems, although it is uncertain whether this calcium effect is mediated via either electrophoretic or cytoskeletal mechanisms. In contrast, the few electrical measurements made on photosynthetic cells suggest that the orientation of their transcellular fields is transiently or permanently reversed relative to the fields in absorptive structures. In darkness, microelectrode measurements indicate that the apical tip of the fern filament is 5 mV electronegative relative to the base of the apical cell. This cellular dipole is perceived with the vibrating probe as a focused outward current that departs from the tip region and a more diffuse inward current that enters the lateral sides of the apical cell. The tip current is predominantly composed of protons, as can be identified with various cation-selective electrodes. This proton current is thought to help maintain localized wall expansion in the filament tip. Blue light mediates the major morphogenetic transition in fern gametophytes, i.e. the transition from the tip-growing filament to the planar prothallus. All the above electrical and ionic parameters change in the few minutes of irradiation before the filament tip starts lateral swelling. The plasma membrane at the extreme tip begins to hyperpolarize within 3 s, while the basal region shows a delayed, but greater response. The cellular dipole that had existed in darkness is thus abolished in 10 to 15 min after the start of irradiation. With the vibrating probe a more diffuse pattern of positive currents is observed to emerge from the tip as well as the subapical regions of the apical cell. Simultaneously, proton efflux increases in the subapical region; the resulting decrease in cell wall pH should help plasticize the lateral walls, which may, in turn, facilitate the process of lateral swelling over the next few hours.(ABSTRACT TRUNCATED AT 400 WORDS)

Electric Conductivity↗
PubMed1982

Electrical Changes in the Apical Cell of the Fern Gametophyte during Irradiation with Photomorphogenetically Active Light.

Electrophysiological procedures were used to evaluate cellular responses of fern (Onoclea sensibilis L.) gametophytes to photomorphogenetically active light. Red, far red, and blue light caused rapid changes in the membrane potential of the apical cell of the gametophyte filament; other cells in the filament were not similarly responsive. Measurements made with one electrode in the apical cell revealed that the membrane potential depolarized in red light and repolarized in far red light. Irradiation with blue light caused a hyperpolarization, the rapidity of which was dependent on a red light pretreatment. More refined measurements with one electrode in the tip of the apical cell and another in the base of the cell showed that both red and blue light treatments cause the apical cell to behave as a dipole. Because of the profound, long-term morphological changes that follow light irradiation in this organism, it was hoped to use it to elucidate the role that electrical parameters play in determining subsequent developmental events.

Journal Article↗
PubMed1977

Mechanism of pancreatic polypeptide release in man.

Pancreatic polypeptide (P.P.) is a potent hormonal peptide which has been isolated from the pancreas. Its role in human physiology and pathology is not yet established. After a standard hospital lunch the plasma concentration of P.P. showed a rapid and identical rise in 10 healthy controls, 11 duodenal-ulcer patients, and 6 post-vagotomy patients but remained undetectable in 4 totally pancreatectomised subjects. In contrast plasma-P.P. was unaffected by intravenous administration of glucose, aminoacids, or fat. However, during intravenous infusion of caerulein, a cholecystokinin analogue, P.P. rose by nearly five-fold, and an even greater rise was seen after intravenous injection of Boots secretin. In 19 duodenal-ulcer patients insulin hypoglycaemia produced a rapid rise in plasma-P.P. but this did not occur in any of the 17 patients studied after a truncal vagotomy. Thus P.P. is released by oral but not intravenous nutriments and the existence of an entero-P.P. axis is postulated. One component of this axis may be the vagal innervation but the normal postprandial rise seen after vagotomy suggests that other control mechanisms, such as the intestinal hormones, are more important.

Adult↗