PubMed Health⌕ Search

Biomedical subjects

M C Ball

Publications and source records attributed to M C Ball.

15 recordsLinked to original sources
PubMed2006

Freeze/thaw-induced embolism depends on nadir temperature: the heterogeneous hydration hypothesis.

Freeze/thaw-induced embolism was studied in leaves of field-grown snow gum (Eucalyptus pauciflora) subject to frequent morning frosts. Juvenile trees were grown in buried pots, brought to the laboratory at different stages of acclimation and subjected to simulated frost-freezes (at 2 degrees C h(-1)) to nadir temperatures of -3 or -6 degrees C, which snow gums commonly experience. Frost-frozen and subsequently thawed leaves were cryo-fixed to preserve the distribution of water and were then examined by cryo-scanning electron microscopy. No embolisms were found in leaves frozen to -3 degrees C and thawed. In contrast, 34% of vessels were embolized in thawed leaves that had been frozen to -6 degrees C. This difference was seen also in the extent of extracellular ice blocks in the mid-vein expansion zones in leaves frozen to -3 and -6 degrees C, which occupied 3 and 14% of the mid-vein area, respectively. While the proportion of embolism depended on nadir temperature, it was independent of season (and hence of acclimation state). From the observation that increased embolism at lower nadir temperature was related to the freeze-induced redistribution of water, we hypothesize that the dehydration of cell walls and cells caused by the redistribution exerts sufficient tension on xylem water to induce cavitation on thawing.

Adaptation, Physiological↗
PubMed2003

A method for assessing occupational exposure to power-frequency magnetic fields for electricity generation and transmission workers.

A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 microT respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer.

Electric Wiring↗
PubMed2000

Protection and storage of chlorophyll in overwintering evergreens.

How evergreen species store and protect chlorophyll during exposure to high light in winter remains unexplained. This study reveals that the evergreen snow gum (Eucalyptus pauciflora Sieb. ex Spreng.) stores and protects its chlorophylls by forming special complexes that are unique to the winter-acclimated state. Our in vivo spectral and kinetic characterizations reveal a prominent component of the chlorophyll fluorescence spectrum around 715 nm at 77 K. This band coincides structurally with a loss of chlorophyll and an increase in energy-dissipating carotenoids. Functionally, the band coincides with an increased capacity to dissipate excess light energy, absorbed by the chlorophylls, as heat without intrathylakoid acidification. The increased heat dissipation helps protect the chlorophylls from photo-oxidative bleaching and thereby facilitates rapid recovery of photosynthesis in spring.

Acclimatization↗
PubMed2000

Leaf respiration of snow gum in the light and dark. Interactions between temperature and irradiance.

We investigated the effect of temperature and irradiance on leaf respiration (R, non-photorespiratory mitochondrial CO(2) release) of snow gum (Eucalyptus pauciflora Sieb. ex Spreng). Seedlings were hydroponically grown under constant 20 degrees C, controlled-environment conditions. Measurements of R (using the Laisk method) and photosynthesis (at 37 Pa CO(2)) were made at several irradiances (0-2,000 micromol photons m(-2) s(-1)) and temperatures (6 degrees C-30 degrees C). At 15 degrees C to 30 degrees C, substantial inhibition of R occurred at 12 micromol photons m(-2) s(-1), with maximum inhibition occurring at 100 to 200 micromol photons m(-2) s(-1). Higher irradiance had little additional effect on R at these moderate temperatures. The irradiance necessary to maximally inhibit R at 6 degrees C to 10 degrees C was lower than that at 15 degrees C to 30 degrees C. Moreover, although R was inhibited by low irradiance at 6 degrees C to 10 degrees C, it recovered with progressive increases in irradiance. The temperature sensitivity of R was greater in darkness than under bright light. At 30 degrees C and high irradiance, light-inhibited rates of R represented 2% of gross CO(2) uptake (v(c)), whereas photorespiratory CO(2) release was approximately 20% of v(c). If light had not inhibited leaf respiration at 30 degrees C and high irradiance, R would have represented 11% of v(c). Variations in light inhibition of R can therefore have a substantial impact on the proportion of photosynthesis that is respired. We conclude that the rate of R in the light is highly variable, being dependent on irradiance and temperature.

Carbon Dioxide↗
PubMed2000

A randomized controlled trial of strapping to prevent post-stroke shoulder pain.

OBJECTIVE: To determine whether strapping the shoulder in hemiplegic stroke patients: (1) prevents the development, or reduces the severity, of shoulder pain, (2) preserves range of movement in the shoulder, and (3) improves the functional outcomes for the arm and patient overall. DESIGN: A prospective, randomized, single-blind controlled trial of shoulder strapping versus no strapping. SETTING: Care of the elderly wards in a teaching hospital, Christchurch, New Zealand. SUBJECTS: All patients admitted with an acute hemiplegic stroke, who had persisting weakness of shoulder abduction. INTERVENTION: The treatment group had their affected shoulder strapped for six weeks from randomization in addition to standard physiotherapy. MAIN OUTCOME MEASURES: All subjects were assessed at entry (week 0), at end of the treatment phase (week 6) and two months later (week 14). A visual analogue scale (VAS) was used to assess shoulder pain severity whereas shoulder range of movement to the point of pain (SROMP) assessed passive range of movement and pain. Functional Independence Measure (FIM), Motor Assessment Scale (MAS) and Rankin Disability Index measured functional outcomes. RESULTS: Ninety-eight subjects participated (49 strapped, 49 controls). Intention to treat analysis showed no significant difference in pain, range of movement or functional outcomes after the intervention phase or at the final assessment. However there were trends for less pain at six weeks (VAS, p = 0.11) and better final upper limb function (MAS, p = 0.16) in strapped patients. Skin reactions were uncommon (6.1%). The presence of neglect or sensory loss, but not subluxation, at baseline was independently associated with poor outcome. Range of movement was lost early (mean difference SROMP between hemiplegic and contralateral shoulders at baseline = 15.2 degrees (95% CI 10.9-19.5)) and continued throughout the study. Shoulder strapping did not alter the rate at which range of movement was lost. CONCLUSIONS: No significant benefit with shoulder strapping was demonstrated and reasons for this are discussed. Range of movement in the hemiplegic shoulder is lost very early and any preventive treatments need to begin within the first 1-2 days after a stroke.

Aged↗
PubMed1999

An analysis of falls in the hospital: can we do without bedrails?

OBJECTIVES: To determine the effects of introduction of a bedrail policy, and an educational program, on patient falls and fall-related injuries. DESIGN: A prospective "Before and After" design. PARTICIPANTS AND SETTING: All patients admitted during 1 calendar year in an assessment, treatment, and rehabilitation unit for older people. INTERVENTION: A policy change for the use of bedrails (restricting their use) and an educational program about their effects. MEASUREMENTS: Patient fall rates -- all falls and around the bed falls -- and patient and staff injuries. RESULTS: There was a significant reduction in the number of beds with bedrails attached after the policy introduction (mean of 40/135 vs 18.5/135, respectively, P = .02), but the fall rate (either total or around the bed) did not change significantly. Serious injuries were significantly less common after the bedrail policy was introduced (P = .008), with fewer head injuries. CONCLUSIONS: Reducing the use of bedrails did not alter patient fall rates significantly, but it was associated with a reduction in serious injuries. Unless it can be shown that bedrails are beneficial, their continued use in older patients must be seriously questioned.

Accidental Falls↗
PubMed1987

Dimerization of 2,6-dimethoxyphenol by Aspergillus flavus: evidence for the reaction occurring close to mycelia.

Aspergillus flavus grown on 2,6-dimethoxyphenol as sole carbon source produced tetramethoxy-p-dibenzoquinone by a free radical mechanism. The product was identified by H-nmr and ms. Scanning electron microscopy and light microscopy were used to follow the growth of mycelia and the attachment of crystals to the mycelial surfaces. Formation of dimer was inhibited by the presence of glucose in the medium.

Aspergillus flavus↗
PubMed1985

Electron Spin Resonance Studies of Ionic Permeability Properties of Thylakoid Membranes of Beta vulgaris and Avicennia germinans.

Measurement of intrathylakoid aqueous volumes by electron spin resonance spectroscopy was used to study ionic permeability properties of thylakoid membranes isolated from Beta vulgaris L. and Avicennia germinans L. The thylakoids behaved as perfect osmometers in the presence of sorbitol and betaine. Thylakoids exposed to hypertonic solutions of NaCl and KCl shrank and subsequently swelled, requiring 10 minutes to regain their original volume. The initial influx rate calculated from the kinetics of changes in intrathylakoid volume in response to 450 millimolar gradients of NaCl and KCl was 2.3 x 10(-13) moles per square centimeter per second. These data show that the passive permeability to NaCl and KCl was low.

Journal Article↗
PubMed1984

Photosynthetic and Stomatal Responses of Two Mangrove Species, Aegiceras corniculatum and Avicennia marina, to Long Term Salinity and Humidity Conditions.

Gas exchange characteristics were studied in two mangrove species, Aegiceras corniculatum (L.) Blanco and Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke, grown under a variety of salinity and humidity conditions. The assimilation rate was measured as a function of the intercellular CO(2) concentration [A(c(i)) curve]. The photosynthetic capacity decreased with increase in salinity from 50 to 500 millimolar NaCl, as shown by decline in both the initial linear slope and the upper plateau of the A(c(i)) curve, with A. corniculatum being the more sensitive species. The decline in photosynthetic capacity was enhanced by increase in the leaf to air vapor pressure difference from 6 to 24 millibars, but this treatment caused a decrease in only the upper plateau of the A(c(i)) curve. Stomatal conductance was such that the intercellular CO(2) concentration obtaining under normal atmospheric conditions occurred near the transition between the lower linear and upper plateau portions of the A(c(i)) curves. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate, which declined with increasing salinity and decreasing humidity. The marginal water cost of carbon assimilation was similar in most treatments, despite variation in the water loss/carbon gain ratio.

Journal Article↗
PubMed1984

Photosynthetic and Stomatal Responses of the Grey Mangrove, Avicennia marina, to Transient Salinity Conditions.

Measurements of gas exchange characteristics were made on intact, attached leaves of hydroponically grown seedlings of Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke as the NaCl concentration of the culture solution was varied by step changes of 50 millimolar NaCl every 2nd day from 50 to 500 to 50 millimolar NaCl. The CO(2) assimilation rate, stomatal conductance, intercellular CO(2) concentration, and evaporation rate decreased at salinities above 250 millimolar NaCl and recovered substantially upon return to the original salinity.The assimilation rate was measured as a function of the intercellular CO(2) concentration [A(c(i)) curve]. The lower linear portion of this curve was insensitive to variation in salinity, whereas the upper nonlinear portion declined with increasing salinity, indicating a reduction in the capacity for CO(2) assimilation which recovered upon return to the original salinity. Stomatal conductance changed such that the intercellular CO(2) concentration measured under normal atmospheric conditions occurred in the transition between the lower, linear and upper nonlinear portions of the A(c(i)) curve. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate. The changes in gas exchange characteristics were such that water loss was minimal relative to carbon gain.

Journal Article↗
PubMed1984

Properties of Thylakoid Membranes of the Mangroves, Avicennia germinans and Avicennia marina, and the Sugar Beet, Beta vulgaris, Grown under Different Salinity Conditions.

Properties of thylakoids isolated from leaves of three salt tolerant species, Avicennia germinans L., Avicennia marina var resinifera, and Beta vulgaris L., were not affected by the salinity in which the plants were grown. With increase in the growth salinity from 50 to 500 millimolar NaCl, there were no major effects on the per chlorophyll concentrations of lipids or proteins, or on the rates of uncoupled electron transport per chlorophyll mediated by either the whole chain or the partial reactions of photosystems I and II. Responses of the partial and whole chain reactions to variation in the sorbitol and NaCl concentrations in the assay media were independent of the salinity experienced during leaf growth and not substantially different from those of a salt-sensitive species, Cucurbita sativus L. Uncoupled rates of electron flow from water to p-benzoquinone mediated by photosystem II were insensitive to the NaCl concentration unless thylakoids were rendered Cl(-) deficient by treatment with uncoupler under alkaline conditions. Loss of 65% to 85% of the photosystem II activity in these Cl(-)-deficient thylakoids was restored by addition of 10 to 20 millimolar Cl(-).

Journal Article↗
PubMed1982

Photosynthetic Responses to Irradiance by the Grey Mangrove, Avicennia marina, Grown under Different Light Regimes.

Photosynthetic responses to irradiance by the grey mangrove, Avicennia marina (Forstk.) Vierh var. australasica (Walp.) Moldenke, were studied using seedlings grown under natural understory shade and exposed conditions as well as in the laboratory under high and low light regimes, i.e. 100% and 6% sunlight, respectively. Leaves in exposed locations were subjected to daylight quantum flux densities greater than 1,000 microeinsteins per square meter per second from 0900 to 1700 hours, whereas those in understory shade experienced only 30 to 120 microeinsteins per square meter per second, interrupted for brief periods by sunflecks ranging in quantum flux density from 800 to 1,500 microeinsteins per square meter per second. The low light regime was similar in light intensity to that of the understory environment, but lacked sunflecks.Leaves from the understory environment showed several properties of ;shade' leaves; i.e. they contained more chlorophyll on both a leaf area and fresh weight basis but had a lower specific weight and greater area than exposed leaves, and were enriched in chlorophyll b relative to a. However, there were no significant differences in either the gas exchange or leaf chlorophyll fluorescence characteristics of the two populations, both being typical of ;sun' leaves.Leaves grown in the laboratory under low and high light regimes had similar properties. However, light saturated assimilation rates in the leaves from the low light treatment were 20% less and became light saturated at a lower quantum flux density than those of leaves grown under the high light regime. The ecological significance of these results is discussed.

Journal Article↗
PubMedDate not supplied

Transfer of PCDD/PCDF from contaminated soils into carrots, lettuce and peas.

In a field experiment, the PCDD/PCDF transfer pathways from soil into carrots, lettuce and peas has been investigated. PCDD/PCDF contamination levels in soil varied between 5 ng I-TEq/kg on the control plot and 56 ng I-TEq/kg on the contaminated plot. PCDD/PCDF levels in carrots were threefold higher in the contaminated plot than in the control plot, which was a result of a tenfold increase in the PCDD/PCDF levels of the peel. PCDD/PCDF levels in lettuce and peas were not higher when grown on the contaminated plot and were much lower than in carrots, which indicates that the PCDD/PCDF in lettuce and peas from both plots are of atmospheric origin.

Air Pollutants↗