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Biomedical subjects

J Fuhrer

Publications and source records attributed to J Fuhrer.

65 records · Page 4Linked to original sources
PubMed1988

The Regulation of Photosynthesis in Leaves of Field-Grown Spring Wheat (Triticum aestivum L., cv Albis) at Different Levels of Ozone in Ambient Air.

Wheat (Triticum aestivum L. cv Albis) was grown in open-top chambers in the field and fumigated daily with charcoal-filtered air (0.015 microliters per liter O(3)), nonfiltered air (0.03 microliters per liter O(3)), and air enriched with either 0.07 or 0.10 microliters per liter ozone (seasonal 8 hour/day [9 am-5 pm] mean ozone concentration from June 1 until July 10, 1987). Photosynthetic (14)CO(2) uptake was measured in situ. Net photosynthesis, dark respiration, and CO(2) compensation concentration at 2 and 21% O(2) were measured in the laboratory. Leaf segments were freeze-clamped in situ for the determination of the steady state levels of ribulose 1,5-bisphosphate, 3-phosphoglycerate, triose-phosphate, ATP, ADP, AMP, and activity of ribulose, 1,5-bisphosphate carboxylase/oxygenase. Photosynthesis of flag leaves was highest in filtered air and decreased in response to increasing mean ozone concentration. CO(2) compensation concentration and the ratio of dark respiration to net photosynthesis increased with ozone concentration. The decrease in photosynthesis was associated with a decrease in chlorophyll, soluble protein, ribulose bisphosphate carboxylase/oxygenase activity, ribulose bisphosphate, and adenylates. No decrease was found for triose-phosphate and 3-phosphoglycerate. The ratio of ATP to ADP and of triosephosphate to 3-phosphoglycerate were increased suggesting that photosynthesis was limited by pentose phosphate reductive cycle activity. No limitation occurred due to decreased access of CO(2) to photosynthetic cells since the decrease in stomatal conductance with increasing ozone concentration did not account for the decrease in photosynthesis. Ozonestressed leaves showed an increased degree of activation of ribulose bisphosphate carboxylase/oxygenase and a decreased ratio of ribulose bisphosphate to initial activity of ribulose bisphosphate carboxylase/oxygenase. Nevertheless, it is suggested that photosynthesis in ozone stressed leaves is limited by ribulose bisphosphate carboxylation possibly due to an effect of ozone on the catalysis by ribulose bisphosphate carboxylase/oxygenase.

Journal Article↗
PubMed1988

Achromobacter xylosoxidans (Alcaligenes xylosoxidans subsp. xylosoxidans) bacteremia associated with a well-water source: case report and review of the literature.

A case of community-acquired Achromobacter xylosoxidans bacteremia in a patient with metastatic breast carcinoma is described. The patient's home drinking water was identified as the source of her bacteremia. The case represents the first in which a community-acquired infection due to this organism has been attributed to a documented water source.

Aged↗
PubMed1986

Fulminant community-acquired infectious diseases: diagnostic problems.

The processes presented here do not represent an all-inclusive list of fulminant infectious diseases. Some of the more common acute, overwhelming infections of the central nervous system and lungs are covered elsewhere in this issue. We have selected less common, potentially catastrophic syndromes that might be recognized earlier if certain historical clues, physical findings, or laboratory abnormalities are appreciated. Specific and effective therapy is available for most of the diseases we have chosen. Meningitis due to Naegleria fowleri, a free-living ameba that may invade the central nervous system through the cribriform plate in persons swimming in brackish water, and hemorrhagic mediastinitis due to inhalation of Bacillus anthracis, which is acquired in occupational exposure to goat's hair, wool, or an animal with anthrax, are other examples but are lacking in proven effective therapy. Although most physicians quickly consider exotic and overwhelming infections in the severely compromised patient, fewer recognize this risk in the diabetic, cirrhotic, or healthy person with a unique occupational or travel history. During the present epidemic of AIDS, previous exposure to the HTLV-3 virus must be considered in all severely ill patients. The proper use of new diagnostic tests may permit the physician to intercede effectively if these life-threatening diseases are suspected.

Deglutition Disorders↗
PubMed1982

Ethylene Biosynthesis and Cadmium Toxicity in Leaf Tissue of Beans (Phaseolus vulgaris L.).

Stress ethylene production in bean (Phaseolus vulgaris L., cv. Taylor's Horticultural) leaf tissue was stimulated by Cd(2+) at concentrations above 1 micromolar. Cd(2+)-induced ethylene biosynthesis was dependent upon synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase. Activity of ACC synthase and ethylene production rate peaked at 8 h of treatment. The subsequent decline in enzyme activity was most likely due to inactivation of the enzyme by Cd(2+), which inhibited ACC synthase activity in vitro at concentrations as low as 0.1 micromolar. Decrease in ethylene production rate was accompanied by leakage of solutes and increasing inhibition of ACC-dependent ethylene production. Ca(2+), present during a 2-hour preincubation, reduced the effect of Cd(2+) on leakage and ACC conversion. This suggests that Cd(2+) exerts its toxicity through membrane damage and inactivation of enzymes. The possibility of an indirect stimulation of ethylene biosynthesis through a wound signal from injured cells is discussed.

Journal Article↗
PubMed1982

Effects of exogenous 1,3-diaminopropane and spermidine on senescence of oat leaves : I. Inhibition of protease activity, ethylene production, and chlorophyll loss as related to polyamine content.

Excision and dark incubation of oat (Avena sativa L., var. Victory) leaves cause a sharp increase in protease activity, which precedes Chl loss. Both these senescence processes are inhibited by exogenously applied 1,3-diaminopropane (Dap), which occurs naturally in leaf segments. The inhibition of protease activity is much greater in vivo than in vitro, suggesting inhibition of protease synthesis as well as protease action by Dap. Chl breakdown in leaves of radish and broccoli, which also senesce rapidly in the dark, is only slightly inhibited by DaP. These differences between cereal and dicotyledonous plants are correlated with the natural occurrence of Dap in cereals. In the light, Dap promotes, rather than retards, the loss of Chl in oat leaves. This resembles previously described effects of other polyamines. Addition of Mg(2+) to the medium does not antagonize this effect. In the dark, the accumulated Dap also inhibits ethylene production and decreases titer of other polyamines. Addition of Ca(2+) to the incubation medium containing Dap competitively reduces the effects of Dap. Thus, Dap, like other polyamines, seems to require an initial attachment to a membrane site shared with Ca(2+) before exerting its antisenescence action.

Journal Article↗
PubMed1982

Effects of Exogenous 1,3-Diaminopropane and Spermidine on Senescence of Oat Leaves : II. Inhibition of Ethylene Biosynthesis and Possible Mode of Action.

The effects of the polyamines spermidine and 1,3-diaminopropane on ethylene biosynthesis and chlorophyll (Chl) loss were studied in peeled leaves of oat (Avena sativa L., var. Victory) incubated in the dark. Peeling off the epidermal cells induces an increase in 1-aminocyclopropane-1-carboxylate (ACC) synthase activity, resulting in an enhanced ACC and ethylene formation. Both polyamines inhibit ethylene biosynthesis from methionine by inhibiting ACC synthase activity and, more effectively, the conversion of ACC to ethylene. They also inhibit Chl loss occurring between 24 and 48 h of dark incubation; but, as shown by inhibitor experiments, inhibition of Chl loss does not result from inhibition of ethylene formation. Ethylene production and Chl loss, both associated with senescence, require membrane integrity; thus, treatments which promote deterioration of membranes inhibit both processes. Ca(2+) in the incubation medium competitively reduces the polyamine-mediated inhibition of ACC conversion and Chl loss. The data suggest that polyamines initially attach to membranes, thereby inducing changes which, in turn, lead to inhibition of ethylene biosynthesis and retardation of senescence.

Journal Article↗
PubMed1980

Uptake of NO2 by plants grown at different salinity levels.

It is demonstrated that the uptake of nitrogen dioxide (NO2) by Phaseolus vulgaris L. is decreased by the addition of sodium chloride (NaCl) to the root medium, as a result of increased diffusive resistance of the leaves. The NO2-uptake rate constant measured kinetically was in agreement with the nitrite content of the leaves after the fumigation.

Biological Transport↗