Biomedical subjects

F T Lichtner

Publications and source records attributed to F T Lichtner.

4 recordsLinked to original sources

PubMed1983

Amitrole Absorption by Bean (Phaseolus vulgaris L. cv ;Red Kidney') Roots : Mechanism of Absorption.

The mechanism of transport of the herbicide 3-amino-1,2,4-triazole (amitrole) into Phaseolus vulgaris roots appears to be passive, as judged by the effect of temperature (Q(10) = 1.3 between 15 and 25 degrees C) and the lack of sensitivity to metabolic inhibition afforded by 2,4-dinitrophenol and NaN(3). Amitrole absorption is a linear function of external concentration over several orders of magnitude and, thus, is not facilitated by a carrier mechanism. The absorption of amitrole is sensitive to external pH, being stimulated under acid conditions. This stimulation of amitrole absorption is seen at low (</=1 millimolar) amitrole concentrations, but not at high (50 millimolar) amitrole levels. While the apparent octanol-water partition coefficient varies with the pH of the aqueous phase, there is no clear correspondence between absorption and the apparent partition coefficient. Roots do not accumulate amitrole above concentration equilibrium; however, at a time when the net amitrole content of the root tissue begins to saturate, amitrole can be detected in the xylem stream. On a fresh-weight basis, amitrole absorption by roots is equal to that accomplished by trifoliate-leaf tissue. An estimate of the permeability coefficient (according to the analysis of Tyree et al. 1979 Plant Physiol 63: 367-374) suggests that amitrole possesses near-optimal permeability for an ambimobile solute, on the order of 2.12 (+/- 0.47) x 10(-9) meters per second.

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PubMed1981

Electrogenic sucrose transport in developing soybean cotyledons.

Addition of sucrose to a solution bathing an excised developing soybean cotyledon causes a transient depolarization of the membrane potential, as measured using standard electrophysiological techniques. The magnitude of the depolarization is dependent on the concentration of both sucrose and protons in a manner which suggests carrier mediation; this process has an apparent K(m) for sucrose of about 10 millimolar. Agents interfering with the generation or maintenance of a proton electrochemical gradient eliminate these depolarizations. Electrogenic sugar transport is sensitive to sulfhydryl-modifying reagents; their effect appears to be through a direct interaction with the carrier protein and/or with the process establishing the proton electrochemical gradient across the plasma membrane. p-Chloromercuribenzene sulfonate appears to be a selective inhibitor of the carrier-mediated process itself.

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PubMed1981

Sucrose uptake by developing soybean cotyledons.

Sucrose uptake by excised developing soybean cotyledons shows a biphasic dependence on sucrose concentration. At concentrations less than about 50 millimolar external sucrose, uptake can be described as a carrier-mediated process, with a K(m) of 8 millimolar. At higher external sucrose concentrations, a linear dependence becomes apparent, which suggests the participation of a nonsaturable component in total uptake. Sucrose absorption is dependent on the presence of an electrochemical potential gradient for protons since agents interfering with the generation or maintenance of this gradient (NaN(3) or carbonylcyanide-m-chlorophenyl hydrazone) decrease sucrose transport to a level at or below that predicted from the operation of the noncarrier-mediated process alone. The saturable component of sucrose uptake is also sensitive to the sulfhydryl-modifying compounds N-ethylmaleimide and p-chloro-mercuribenzenesulfonate. The thiol-reducing agent diethioerythritol reverses fully the p-chloro-mercuri-benzenesulfonate inhibition, but not that of N-ethyl maleim de. Sucrose transport is sensitive to external pH, being decreased at high pH(0). Since sucrose-induced depolarization of the membrane potential and carrier-mediated sucrose influx show similar pH-dependence, inhibitor sensitivity, and values of K(m) for sucrose, a sucrose/proton contransport process appears to operate in developing soybean cotyledon cells. Measurement of free space and intracellular sucrose concentrations in vivo suggests that the carrier-mediated process is fully saturated and that sucrose transport may be limiting for sucrose accumulation by the developing seed.

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PubMed1981

Effect of Sulfhydryl Reagents on the Biophysical Properties of the Plasmalemma of Chara corallina.

The administration of the sulfhydryl reagent N-ethyl-maleimide (NEM) to internodal cells of Chara corallina caused alterations in the biophysical properties of the plasmalemma, as measured with electrophysiological and radioactive tracer techniques. The membrane potential depolarized to, or near, the calculated Nernst potential for potassium (E(K)) after 30 seconds' exposure to 0.1 millimolar NEM. During this time, the ATP level did not decrease below the control value, and the specific membrane resistance did not increase; only upon further exposure to NEM did the resistance approach the value observed in the dark. In the depolarized state, the membrane potential responded to changes in the external potassium concentration in the manner of a K(+)-electrode, but it retained it's relative insensitivity to external sodium.THESE RESULTS ARE INTERPRETED IN THE FOLLOWING MANNER: NEM causes a) an increase in the membrane permeability to K(+) (i.e. an increase in K(+) conductance); and b) perturbation of the electrogenic transport system(s) of the plasma membrane. The latter effect is manifested in a manner that is not consistent with an inhibition of ATP catalysis by a voltage-dependent ATPase possessing conductance. The nonpermeant sulfhydryl modifier, p-chloromercuribenzenesulfonic acid, appeared to affect membrane properties in a similar, but reversible, way.

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