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Biomedical subjects

M G Jones

Publications and source records attributed to M G Jones.

99 records · Page 6Linked to original sources
PubMed1977

Enzymic assay of 10 to 10 moles of sucrose in plant tissues.

Procedures are described for measuring sucrose in plant extracts or freeze-dried tissue in the range between 10(-7) and 10(-14) moles. The method is based on the destruction of pre-existing glucose and fructose, followed by the hydrolysis of sucrose and reduction of NADP(+) by a series of coupled enzymic reactions. Depending on the sensitivity required, the NADPH is determined directly with a spectrophotometer or a fluorometer, or is amplified as much as 30,000 times before fluorometric assay. The procedures suggested for the macro level are simpler than current methods, and those suggested for microanalysis are several orders of magnitude more sensitive.With this technique, single palisade parenchyma cells and single spongy parenchyma cells of Vicia faba leaflets were each found to contain about 2.2 pmoles of sucrose.

Journal Article↗
PubMed1977

The structure of syncytia induced by the phytoparasitic nematode Nacobbus aberrans in tomato roots, and the possible role of plasmodesmata in their nutrition.

The structure of syncytia induced within galls in tomato roots by the false root-knot nematode Nacobbus aberrans has been examined by light and electron microscopy. A syncytium develops by breakdown or individual cell walls, which allows movement of cytoplasmic contents between transformed cells. The wall breakdown takes place at pit fields, where the plasmodesmata may be protected from digestion until the surrounding wall is removed. Numerous sieve elements differentiate in the cells outside the syncytium. These sieve elements, and also plasmodesmata in pit fields, are demonstrated by fluorescence microscopy. The possibility of a symplastic pathway of solute movement from the phloem to the syncytium is suggested. A massive accumulation of starch occurs in the gall cells and syncytial cells, which may be related to the proliferation of phloem. Wall ingrowths typical of transfer cells are absent, and a comparative survey of the structure and mode of solute entry into nematode-transformed cells in which ingrowths are present or absent is presented.

Cell Differentiation↗
PubMed1976

Scanning electron microscopy in nematode-induced giant transfer cells.

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells.

Autoradiography↗
PubMedDate not supplied

Stopped-flow studies of cytochrome oxidase reconstituted into liposomes: proton pumping and control of activity.

The transient kinetics of proton pumping and the electron transfer properties of cytochrome oxidase inserted into small unilamellar vesicles have been investigated by stopped-flow spectrophotometry. In the presence of valinomycin, proton pumping and cytochrome c oxidation by cytochrome oxidase are synchronous up to rate constants of approximately 9 sec-1. Moreover, the enzyme depleted of subunit III ("three-less oxidase") was also shown to pump protons, although with a significantly smaller stoichiometry. Thus, subunit III is not the only (or even the main) proton channel, although it may be involved in the regulation of activity. The kinetics of cytochrome c oxidation by COV in the absence and in the presence of ionophores have been investigated. Analysis of the time course of the process in the transient and steady state phases indicates that the onset of control by the electrochemical gradient follows the transfer of four electrons, i.e., one complete turnover of the oxidase. Two possible alternative interpretations for the control of the turnover phase are presented and discussed.

Animals↗
PubMedDate not supplied

Chemical models for the lethality curves of toxic metal ions.

Several equilibrium models are presented for the calculation of the lethality curves due to toxic metal ions. In the first, a generalized Langmuir model is used to examine the occupancy of linear arrays of 1, 2, ..., 6 interacting adsorption sites on a macromolecular species. This model permits one to take into account cooperative or anticooperative interaction of occupied adjacent sites. In the second model, a variety of nonlinear distributions of interacting sites (in triangular, square, tetrahedral, and octahedral array) are analyzed, and the corresponding adsorption isotherms are calculated. The third model treated, the Ising model, represents a linear infinite array of sites with nearest-neighbor interactions. The fourth and fifth models examined are the Bragg-Williams model and the quasi-chemical model, both of which permit approximate treatment of infinite arrays of adsorption sites having arbitrary numbers of interacting nearest neighbors. These models are then combined with the assumption that the differential distribution of mortality is a known function of the fraction of sites occupied by the toxic metal ion to generate lethality curves. Results are computed for the special case in which the differential mortality distribution is Gaussian, and it is shown that all of the models are capable of generating lethality curves of the sort found experimentally when plots are made of percentage lethality versus log dosage. The models can also be used for situations in which toxic effects other than lethality arise from the interaction of a toxic molecule or ion with more than one site on a linear macromolecule or for reactions involving certain other arrays of specified configuration.

Binding Sites↗
PubMedDate not supplied

Telemedicine and the national information infrastructure: are the realities of health care being ignored?

Health care is shifting from a focus on hospital-based acute care toward prevention, promotion of wellness, and maintenance of function in community and home-based facilities. Telemedicine can facilitate this shifted focus, but the bulk of the current projects emphasize academic medical center consultations to rural hospitals. Home-based projects encounter barriers of cost and inadequate infrastructure. The 1996 Telecommunications Act as implemented by the Federal Communications commission holds out significant promise to overcome these barriers, although it has serious limitations in its application to health care providers. Health care advocates must work actively on the federal, state, and local public and private sector levels to address these shortcomings and develop cost effective partnerships with other community-based organizations to build network links to facilitate telemedicine-generated services to the home, where the majority of health care decisions are made.

Community Networks↗
PubMedDate not supplied

New avenues in 3-D computerised (stereopathological) imaging of breast cancer (review).

Multimodal methods of three-dimensional (3-D) imaging of breast cancer are described. These involve scanning confocal microscopy, using 50 MHz acoustic or near-infrared images, four-view (tetrahedral) radiography and x-ray projection microscopy. Computerised volume data from these techniques can be used to produce three-dimensional images of tissue ranging from 500 microns to approximately 4 mm in thickness. Preliminary findings indicate that stereoscopic images or 3-D computerised reconstructions are capable of advancing the understanding of the structure of ductal carcinoma in situ, lesions simulating microinvasive breast carcinoma, surgical clearance of high-grade calcifying ductal carcinoma in situ, and the 3-D growth patterns of invasive forms of breast carcinoma. In the future computerised image fusion techniques seem likely to be able to take advantage of multimodal imaging of breast cancers, thus correcting primary imaging artefacts, improving robustness, and combining complementary information. In addition, the use of computerised tetrahedral radiography may change the intraoperative assessment of breast cancers, which mostly depend at present upon subsequent laboratory procedures that take days to perform.

Breast Neoplasms↗