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Biomedical subjects

A R Wellburn

Publications and source records attributed to A R Wellburn.

17 recordsLinked to original sources
PubMed1996

Manipulation of glutathione metabolism in transgenic plants.

There is clear potential for the genetic manipulation of key enzymes involved in stress metabolism in transgenic plants. However, the data emerging so far from such experiments are equivocal. The detailed analysis of stress responses in progeny of primary transgenics, coupled with comparisons with control transgenic plants that do not contain the GR transgene, allows us to take into account the possible variation in response to stress associated with regeneration of plants from tissue culture. The picture that is now beginning to emerge with respect to the role of GR in stress protection is that, although there are clearly benefits to be had from overexpression of the enzymes, there is no direct correlation between enzyme levels and stress tolerance. It may be that overexpression of the cytosolic isoform (gor2) will prove to be of greater benefit. Furthermore, the types of stresses to which transgenic plants have been exposed in order to assess the consequences of oxidative stress tolerance cannot reproduce those that will experienced in field conditions. Only when plants with higher GR levels and increased glutathione synthesis capacity are grown in field trials will it be possible to make a full assessment of the benefits of engineering plants with altered glutathione metabolism.

Amino Acid Sequence↗
PubMed1991

Relationship between foliar injury and changes in antioxidant levels in red and Norway spruce exposed to acidic mists.

Elevated levels of total glutathione and enhanced activities of glutathione reductase and ascorbate peroxidase were found in needles of red spruce which had been exposed to acidic mists. Reduced levels of ascorbate were also detected. Such observations suggest that oxidative stress is involved in processes which resist foliar injury caused by acidic misting. Different ionic compositions of the acidic mists applied had pronounced effects on the levels of these antioxidants and the activities of related enzymes. Sulphate was found to be most effective in causing increases in glutathione, while additions of ammonium and/or nitrate mitigated the effects of sulphuric acid. Moreover, it is the composition of ions in the applied mists, rather than the levels of acidity, that determines the extent of the overall response of red spruce. By contrast, although acidic mists caused similar increases in glutathione content of Norway spruce needles, no statistically significant changes of ascorbate or related enzymic activities were found.

Journal Article↗
PubMed1989

Enhanced ethylene emissions from red and norway spruce exposed to acidic mists.

Acidic cloudwater is believed to cause needle injury and to decrease winter hardiness in conifers. During simulations of these adverse conditions, rates of ethylene emissions from and levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in both red and Norway spruce needles increased as a result of treatment with acidic mists but amounts of 1-malonyl(amino)cyclopropane-1-carboxylic acid remained unchanged. However, release of significant quantities of ethylene by another mechanism independent of ACC was also detected from brown needles. Application of exogenous plant growth regulators such as auxin, kinetin, abscisic acid and gibberellic acid (each 0.1 millimolar) had no obvious effects on the rates of basal or stress ethylene production from Norway spruce needles. The kinetics of ethylene formation by acidic mist-stressed needles suggest that there is no active inhibitive mechanism in spruce to prevent stress ethylene being released once ACC has been formed.

Journal Article↗
PubMed1987

Induction of ascorbate peroxidase and glutathione reductase activities by interactions of mixtures of air pollutants.

The response of ascorbate peroxidase and glutathione reductase activities in peas (Pisum sativum var. Waverex) was investigated after three weeks of exposure to mixed fumigations with SO2, NO2 and O3 (0.050 parts per million each) and increasing concentrations of O3 (0-0.150 parts per million). The results show that plants respond similarly to a high concentration (0.150 parts per million) of a single air pollutant (ozone) and to mixtures of air pollutants (SO2, NO2 and O3) when individual concentrations are low (0.050 parts per million each). In both cases, levels of ascorbate peroxidase and glutathione reductase activities were approximately twice those to be found in plants grown in charcoal-filtered air (p less than 0.01).

Air Pollutants↗
PubMed1985

Oxides of nitrogen and their impact upon vegetation.

Annual and daily levels of the two major oxides of nitrogen (NOX), nitric oxide (NO) and nitrogen dioxide (NO2) are still rising in the atmosphere of the urban environment and in close proximity to automobile and airport traffic. Although oxides of nitrogen give rise to other phytotoxic pollutants such as ozone they are also in their own right damaging to plant health. This injury is not normally visible but is reflected in poorer growth and loss of productivity in terms of value and amenity. Few if any reviews have considered the effects of atmospheric concentrations of NOX as separate phytotoxic agents especially at the metabolic level. This paper is an attempt to remedy this deficiency and to promote an understanding of the problem.

Air Pollutants↗
PubMed1979

Appearance of photochemical function in prothylakoids during plastid development.

1. A method to separate the vesicles of prothylakoids from prolamellar body preparations obtained from etiolated and rapidly greening Avena laminae (0.25--4 h illumination ) is described. The prothylakoid preparations were found to be free from contaminating prolamellar bodies but enriched prolamellar body preparations (enriched prolamellar body preparations) still contained some adhering prothylakoid material. 2. Only existing beta-carotene appears to be transferred from the prolamellar bodies to the prothylakoids during early development and this ceases when freshly synthesized beta-carotene becomes available. 3. Prolamellar body structures proper show no positive association of existing or developing photochemical activities; these are only to be found in the developing prothylakoids. 4. Using methylviologen-linked electron transport-dependent oxygen consumption, Photosystem I activities may be detected with added diaminodurene within 15 min of illumination and within 30 min and 1 h with added tetramethylphenylenediamine and dichlorophenolindophenol, respectively. 5. During the 2nd, and 3rd. h of greening, proton-pumping capability and later ATP formation increased in prothylakoids in the presence of diaminodurene. 6. The first indications of Photosystem II activity using diphenylcarbazide as electron donor are shown at a similar time (2 h) with prothylakoids. The last photochemical activity to appear is the capacity to split water (3 h) and consequently the diphenylcarbazide activity diminished to zero before 8 h of illumination have passed. 7. The lack of effect of uncouplers such as NH4+ prior to 2 h suggests that in spite of some proton-pumping ability there is the possibility of proton-leaky areas existing within prothylakoids. This lack of a persistent proton gradient before 2 h of illumination may explain the different starting times of phenazine methosulfate- and diaminodurene-dependent photophosphorylation (0.25 and 2 h, respectively).

Carotenoids↗
PubMed1976

Uptake of mevalonate and acetate during plastid development.

1. The envelopes of etioplasts and 1-2h etiochloroplasts are permeable to mevalonate, but plastids from etiolated tissue illuminated for longer than 4h show progressive impermeability towards mevalonate. 2. Acetate permeates the envelopes of 1-4h etiochloroplasts but does not significantly cross the envelopes of etioplasts or 8-24h etiochloroplasts. 3. A translocator system exists within the plastid envelopes for mevalonate which relies on malate as a counter-exchange anion.

Acetates↗
PubMed1967

The characterization and properties of castaprenol-11, -12 and -13 from the leaves of Aesculus hippocastanum (horse chestnut).

The isolation and purification of a mixture of cis-trans-polyprenols from the leaves of Aesculus hippocastanum (horse chestnut) are described. Results of studies involving mass spectrometry, nuclear magnetic resonance, infrared spectroscopy, micro-hydrogenation and ozonolytic degradation show the mixture to be made up of undecaprenol, dodecaprenol and tridecaprenol with dodecaprenol predominating. Each of the prenols contains three trans internal isoprene residues and a cis ;OH-terminal' isoprene residue. They differ from each other only in the number of cis internal isoprene residues. The trivial names castaprenol-11, castaprenol-12 and castaprenol-13 are proposed to describe these compounds. Gas-liquid-chromatographic and reversed-phase partition thin-layer chromatographic evidence suggest the presence in the mixture of small quantities of castaprenol-10 also.

Acetates↗
PubMed1967

The characterization of ficaprenol-10, -11 and 12 from the leaves of Ficus elastica (decorative rubber plant).

Evidence from mass, nuclear-magnetic-resonance and infrared spectrometry and from gas-liquid and thin-layer chromatography is presented in favour of the presence of cis-trans-decaprenol, -undecaprenol and -dodecaprenol in the mixture of polyprenols (2.6mg./g.) isolated from leaf tissue of Ficus elastica. The trivial names ficaprenol-10, -11 and -12 are proposed. Nuclear-magnetic-resonance studies showed that each of these prenols contains three trans internal isoprene residues and a cis ;OH-terminal' isoprene residue. Ficaprenol-11 is the major component of the mixture. Chromatographic evidence suggests the presence also of small amounts of ficaprenol-9 and -13. The precise position of the three trans internal isoprene residues was not determined but it is suggested that these are adjacent to the omega-terminal isoprene residue and that the ficaprenols are formed from all-trans-geranylgeranyl pyrophosphate. It is also suggested that ficaprenol-10, -11, -12 and -13 are probably the same compounds as castaprenol-10, -11, -12 and -13.

Alcohols↗
PubMed1967

The subcellular distribution and biosynthesis of castaprenols and plastoquinone in the leaves of Aesculus hippocastanum.

Intact chloroplasts and cell walls were prepared from horse-chestnut leaves that had previously metabolized [2-(14)C]mevalonate. The bulk of the castaprenols and plastoquinone-9 was found within the chloroplasts. The remaining portion of the castaprenols was associated with the cell-wall preparation whereas that of the plastoquinone-9 was probably localized in the soluble fraction of the plant cell. The (14)C content of these compounds of different cell fractions indicated the presence of polyisoprenoid-synthesizing activity both inside and outside the chloroplasts. This was confirmed by the relative incorporation of (14)C when ultrasonically treated and intact chloroplasts were incubated with [2-(14)C]mevalonate. As the leaves aged (on the tree) an increase in extraplastidic castaprenols and plastoquinone-9, together with associated synthesizing activities, was observed.

Alcohols↗