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Biomedical subjects

C A Mitchell

Publications and source records attributed to C A Mitchell.

At least 199 records · Page 11Linked to original sources
PubMed1984

Metabolic response of river birch and European birch and European birch roots to hypoxia.

Flood tolerance of woody plants has been attributed to internal oxygen diffusion from shoot to root, metabolic adaptation within the root, or both. The purpose of this study was to compare several biochemical and physiological responses of birch roots to hypoxia in order to determine the nature of root metabolic adaptation to low oxygen tension. One-year-old seedlings of flood-tolerant river birch (Betula nigra L.) and flood-intolerant European birch (Betula pendula Roth) were transferred to solution culture, and the solutions were bubbled with air or nitrogen. After 18 days of hypoxia, total adenosine phosphate and ATP contents of river birch roots were 35% and 23% of controls, respectively, whereas those of European birch roots were 13% and 8%. Adenylate energy charge of river birch roots decreased between 6 and 12 days of hypoxia. In contrast, energy charge of European birch roots decreased after only 1 day of hypoxia. In vitro activity of cytochrome c oxidase and oxygen consumption capacity of excised roots from both birch species decreased under hypoxia. In vitro activity of alcohol dehydrogenase from roots of both species increased after 1 day of hypoxia. However, alcohol dehydrogenase activity from river birch roots increased 25-fold after 6 days of hypoxia, whereas that from European birch decreased back to control levels. Hypoxia decreased malate content of roots from both species. Metabolic adaptation within the root, rather than internal oxygen diffusion, appears to be responsible for the relative tolerance of river birch to hypoxia.

Journal Article↗
PubMed1984

Seismic stress effects on vegetative and reproductive development of 'Alaska' pea.

Vegetative and reproductive growth responses of pea (Pisum sativum L. cv. Alaska) to periodic seismic (shaking) stress were investigated during fall, winter, and spring seasons in a greenhouse. Growth changes caused by equivalent shaking treatment varied quantitatively among seasons, with the least response occurring during winter, but they were qualitatively similar during all three seasons. Shaking caused significant reduction in all growth parameters measured except root dry weight and leaf number after 16 days of treatment. Reproductive growth responses to shaking (occurring from 16 to 35 days of treatment) included delay of anthesis but no difference in number of fruits set after as much as 35 days of treatment. Seismic stress significantly reduced the number but not the weight of individual seeds per pod. Mean relative shoot growth rate was reduced by shaking during reproductive as well as vegetative growth. During both periods of development this response was caused almost entirely by inhibition of net carbon assimilation rate.

Environment, Controlled↗
PubMed1983

Parathion alters incubation behavior of laughing gulls.

One member of each pair of incubating laughing gulls at 9 nests was trapped, orally dosed with either 6 mg/kg parathion in corn oil or corn oil alone, and marked about the neck with red dye. Each nest was marked with a numbered stake and the treatment was recorded. A pilot study with captive laughing gulls had determined the proper dosage of parathion that would significantly inhibit their brain AChE activity (about 50% of normal) without overt signs of poisoning. After dosing, birds were released and the nests were observed for 2 1/2 days from a blind on the nesting island. The activities of the birds at each marked nest were recorded at 10-minute intervals. Results indicated that on the day of treatment there was no difference (P greater than 0.05, Chi-square test) in the proportion of time spent on the nest between treated and control birds. However, birds dosed with 6 mg/kg parathion spent significantly less time incubating on days 2 and 3 than did birds receiving only corn oil. By noon on the third day, sharing of nest duties between pair members in the treated group had approached normal, indicating recovery from parathion intoxication. These findings suggest that sublethal exposure of nesting birds to an organophosphate (OP) insecticide, such as parathion, may result in decreased nest attentiveness, thereby making the clutch more susceptible to predation or egg failure. Behavioral changes caused by sublethal OP exposure could be especially detrimental in avian species where only one pair member incubates or where both members are exposed in species sharing nest duties.

Animals↗
PubMed1983

Stimulation of lettuce productivity by manipulation of diurnal temperature and light.

'Salad Bowl' and 'Waldmann's Green' leaf lettuce (Lactuca sativa L.) were exposed to photosynthetic photon flux densities (PPFD) of 444 or 889 micromoles s-1 m-2 for 20 hours day-1 under a diurnal temperature regime of 25 degrees C days/15 degrees nights or 20 degrees days/15 degrees nights. Leaf dry weight of both cultivars was highest under the high PPFD/warm temperature regime and lowest under the low PPFD/cool temperature regime. 'Waldmann's Green' yielded more than did 'Salad Bowl' at 889 micromoles s-1 m-2 and 25 degrees days/20 degrees nights. Under high PPFD, both cultivars yielded better with 25 degrees days/25 degrees nights than with 25 degrees days/20 degrees nights, although relative growth rates were the same under both temperature regimes.

Biomass↗
PubMed1983

Enhancement of lettuce yield by manipulation of light and nitrogen nutrition.

Several levels of photosynthetic photon flux density (PPFD) were tested for effects on growth of 4 cultivars of lettuce (Lactuca sativa L.) under controlled-environment conditions. Growth of 'Salad Bowl', 'Bibb', and 'Ruby' was greater at 932 micromoles s-1 m-2 than at < or = 644 micromoles s-1 m-2 under a 16-hour photoperiod. Thirty mM NO3- or 5 mM NH4+ + 25 mM NO3- increased leaf dry weight while reducing leaf chlorosis in 'Salad Bowl' and 'Grand Rapids' relative to that with 15 mM NO3-, and reduced leaf purpling in 'Bibb' and 'Ruby' with little or no effect on yield. Continuous illumination with 455 or 918 micromoles s-1 m-2 stimulated yield of 'Salad Bowl' and 'Bibb' when 30 mM N as NH4+ + NO3- was used relative to that with 15 mM NO3-.

Culture Media↗
PubMed1983

Nebulized fenoterol in severe asthma: determinants of the dose response.

We assessed the bronchodilator response to cumulative doses of nebulised fenoterol in 16 patients with severe asthma to determine (1) the magnitude of the bronchodilator response, (2) the factors determining this response, and (3) the dose producing maximum bronchodilation. To reflect the degree to which ventilatory function returned to normal, individual bronchodilator responses were assessed as the change in FEV1 (post-fenoterol FEV1 - initial FEV1) and expressed as a percentage of the predicted maximum response (predicted FEV1 - initial FEV1). The bronchodilator response was extremely varied (about 55% of predicted maximum in six patients, 40% in three patients, and 20% in seven patients), as was the dose producing maximal bronchodilation (1 mg in three patients, 2 mg in six patients, and 2.5 or 3 mg in seven patients). In individual patients the maximum response could be predicted by the response to the initial dose of fenoterol and by the duration of the episode of severe asthma. The maximum response was not predicted by the initial severity of obstruction or the patient's usual treatment.

Administration, Intranasal↗
PubMed1981

Reevaluation of the cyanide resistance of seed germination.

Although high levels of KCN (53 micromoles per gram fresh weight of seed, corresponding to 3.2 millimolar) failed to block germination of lettuce seeds incubated in covered Petri dishes, the same levels totally blocked germination in sealed dishes. Inhibition was reversed by removing the seal. Placement of KCN remote from seeds also blocked germination in closed systems. Cyanide effectiveness was enhanced by acidifying the KCN solution but negated by the presence of a trap containing strong alkali. Low levels of aqueous HCN (2.6 micromoles HCN per gram, corresponding to 0.16 millimolar) injected into sealed dishes gave maximal inhibition of germination, suggesting that the effectiveness of KCN was due to formation of HCN in KCN solutions. Studies with nine additional crop species generally supported the interpretation that cyanide inhibition of germination has been underestimated in the past due to escape of volatile HCN from open systems.

Journal Article↗