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Biomedical subjects

R L Heath

Publications and source records attributed to R L Heath.

At least 37 records · Page 2Linked to original sources
PubMed1981

Ozone Sensitivity in Sweet Corn (Zea mays L.) Plants: A Possible Relationship to Water Balance.

Stomatal characteristics affecting gas exchange were compared in two sweet corn hybrids (var. Bonanza and Monarch Advance) which differ in foliar ozone sensitivity. No significant differences were observed in stomatal frequencies, guard cell lengths, or conductances to water vapor diffusion.When plant water status was compared, leaf-water potentials for the ozone-resistant cultivar, Bonanza, were lower. A comparison of the relationship between soil- and leaf-water potential indicated that the leaf-water potential of Bonanza was more sensitive to declines in soil-water potential. Additionally, a comparison of stomatal conductance to water vapor diffusion as soil moisture declined and following root detachment indicated that stomata of Bonanza were, likewise, more sensitive to increasing water stress. Data suggest that these differences are attributable to a greater shoot-to-root fresh weight ratio and higher resistance to water movement in the water-conducting tissues for Bonanza.Our observations suggest that root and water delivery system characteristics play a major contributory role in the determination of foliar ozone sensitivity in this species.

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PubMed1979

A Constitutive Enzyme System for Glucose Transport by Chlorella sorokiniana.

It was found that the transport system for glucose (as measured by deoxyglucose uptake) in the high temperature strain of Chlorella (strain 07-11-05 or C. sorokiniana) was constitutive and the rate of uptake did not increase upon incubation of autotrophically grown cells with either deoxyglucose or glucose. The uptake obeyed Michaelis-Menten type kinetics with a concentration of 200 micromolar for half-saturation. The maximum rate of uptake was nearly 10 times faster per cell (at 38 C) than that reported for any other Chlorella. This rapid accumulation of deoxyglucose causes the passive efflux to become significant compared to the pump-driven influx and nonlinear uptake appears even after only 3 to 4 minutes.

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PubMed1979

Ozone alteration of membrane permeability in chlorella: I. Permeability of potassium ion as measured by rubidium tracer.

The addition of ozone to a suspension of Chlorella sorokiniana causes a rapid loss of K(+), as measured by efflux of (86)Rb from prelabeled cells. The efflux of the tracer is stimulated some 15 to 20 times over that of the control. For about 100 microliters per liter ozone, about 25 minutes (6 x 10(-8) moles O(3) delivered per minute) of exposure are required for a 50% depletion of the intracellular K(+). The stimulation of K(+) efflux is nearly linearly dependent upon the amount of ozone delivered into the solution. Following short pulses of ozone (lasting 1 to 5 minutes), efflux rates return to the control level but only after about 15 minutes.While influx of K(+) is ultimately inhibited by ozone, at low concentrations or for short exposure times the tracer influex is stimulated 100 to 200%. Ozone stimulation of an active pump mechanism is unlikely in view of a concomitant decrease in respiration. Thus, this influx may represent movement of K(+) along its electrochemical gradient. Assuming that influx and efflux are in steady-state according to the Goldman equation, it was calculated that the membrane potential for K(+) of -80 to -90 millivolts in control cells drops to -40 millivolts with ozone exposure and is accompanied by a calculated increased permeability to K(+) of 2- to 3-fold.

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PubMed1977

Penetration of Mannitol into the Intracellular Space of Chlorella sorokiniana.

It was found that in the alga, Chlorella sorokiniana, mannitol penetrated the plasmalemma (normally thought to be impermeable to mannitol) into the intracellular space. The rate of penetration is exponential and relatively slow, having a half-time of 6 to 12 minutes and requiring over 60 minutes for complete penetration. This penetration was demonstrated both by the Millipore filtration of cells incubated with (14)C-mannitol and by centrifugation of the cells through a silicon oil layer after incubation with tritiated water and (14)C-mannitol. Further, mannitol caused an inhibition of both autotrophic (on CO(2)) and heterotrophic (on glucose) growth. A low rate of mannitol metabolism was demonstrated, although this rate could not support heterotrophic growth.

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PubMed1975

Two mechanisms of near-ultraviolet lethality in Saccharomyces cerevisiae: a respiratory capacity-dependent and an irreversible inactivation.

Near-ultraviolet irradiation of actively growing yeast cells leads to cell death by two distinct mechanisms. The first type of cell death is evident after low doses of near-ultraviolet light (3 times 10-4 ergs times mm- minus 2) and is due to a reversible inactivation of the respiratory capacity of the cell. In studies with yeast mitochondrial membranes the quinones were identified as the site of inactivation by determining the relative levels of the following oxidase activities after irradiation: exogenous NADH, endogenous NADH (via isocitrate dehydrogenase), succinate, and D-lactate oxidases. A second type of cell death is caused after high doses (1.8 times 10-5 ergs times mm- minus 2) and is irreversible. The mechanism of this inactivation is unknown.

Electron Transport↗
PubMed1975

Ozone-induced Fatty Acid and Viability Changes in Chlorella.

Ozone-treated cells of the photosynthetic green alga Chlorella sorokiniana var. pacificensis exhibit an exponential decline in viability, as measured by their ability to form colonies on agar plates. Postexposure conditions appear to have little, if any, effect on this rate of decline. Except in young (early exponential phase) cells, culture age did not affect this rate. The decline in cell viability was correlated with the production of malondialdehyde, arising from the oxidative breakdown of an ozonide of unsaturated fatty acid material. The loss of fatty acids is substantiated by gas-liquid chromatography. A loss of 5 x 10(-15) moles of fatty acid per cell corresponds to 75% nonviable cells after 50 minutes of ozone exposure.

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PubMed1975

Carbonic anhydrase of spinach: studies on its location, inhibition, and physiological function.

Carbonic anhydrase activity was determined in spinach (Spinacia oleracea) leaf organelles isolated on sucrose density gradients and was found to be predominantly in the intact chloroplast fraction. The small amount of activity associated with the mitochondrial fractions was probably due to intact chloroplast contamination. No activity could be associated with the broken chloroplast or microbody fractions. Based upon inhibitor studies, carbonic anhydrase was found to be around 2 mm in the chloroplast. Ethoxzolamide, an inhibitor of carbonic anhydrase, reduced CO(2) fixation in intact chloroplasts. The concentration required to inhibit CO(2) fixation 20 to 40% was in excess of that required to inhibit the purified enzyme. The inhibition was partially reversed by CO(2). Ethoxzolamide had no effect on photosynthetic NADP reduction or photophosphorylation measured by methyl viologen reduction. The physiological role of carbonic anhydrase was shown not to be associated with CO(2) diffusion or CO(2) concentration. It is proposed that other functions of carbonic anhydrase could be the protection against denaturation by transient localized changes in pH or the hydration of compounds other than CO(2).

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PubMed1975

Conversion of Signals from Ion-specific Electrodes to Linear Concentrations.

This paper describes the assembly (from commercially available components) of an antilog converter, which transforms the output signals of ion-specific electrodes to ionic concentrations suitable for a linear recorder. It responds linearly to cation concentrations from 10 mum to at least 10 mm and can be used for electrodes kept at any temperatures (0 to 50 C). The leakage of K(+) from a unicellular algae (Chlorella sorokiniana) can be induced by Triton X-100, heating, or suspension in a tris buffer and is used to demonstrate the operation of this device.

Journal Article↗
PubMed1975

Ozone-induced Loss of Intracellular Potassium Ion from Chlorella sorokiniana.

The unicellular algae Chlorella sorokiniana was used as a model system to investigate the interaction of ozone with plant cell membranes. Ozone induces K(+) leakage from Chlorella sorokiniana similar to the electrolytic loss observed from many higher plants under stressful conditions. The kinetics of this leakage indicate that ozone initially interacts reversibly (within sec) with sites on membranes allowing a passive efflux of K(+). This efflux ceases within minutes after the ozone stress is removed. This return to normal efflux is very temperature dependent. High intracellular osmolarity seems to be an important criterion of susceptibility to ozone injury in this model system, since rates of ozone-induced K(+) leakage are less when the external osmotic potential is decreased by suspension of the cells in mannitol. Cell interaction with ozone is further complicated by a saturating-type dependence of the K(+) efflux upon ozone concentration within the medium.

Journal Article↗
PubMed1974

Inhibition of the photosynthetic capacity of isolated chloroplasts by ozone.

Isolated spinach chloroplasts have been used as a model system for studying the interaction of ozone, a component of photochemical smog, with plant membranes. Ozone bubbled into a suspension of isolated chloroplasts inhibits electron transport in both photosystems without uncoupling ATP production. Photosystem I (reduced 2,6-dichlorophenolindolphenol --> NADP(+)) is a little more sensitive than photosystem II (H(2)O --> 2,6-dichlophenolindolphenol). Ozone does not act as an energy transfer inhibitor, since the drop in ATP production and high energy intermediate (measured by amine-induced swelling) is nearly parallel to the decline in electron transport. A reasonable hypothesis is that ozone disrupts the normal pathway of energy flow from light-excited chlorophyll into the photoacts by a disruption of the components of the membrane but not a general disintegration of the membrane. In addition, ozone does not seem to penetrate into the grana region through the outer membrane of intact plastids, since ozone lowers the bicarbonate-supported O(2) evolution but does not affect the rate of ferricyanide reduction in the same plastids after osmotic disruption. This would indicate that the effect of ozone on green plants, at low concentrations, may be due to the interaction of ozone with the first membrane it contacts and not directly with internal metabolic processes.

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