PubMed Health⌕ Search

Biomedical subjects

R W Fisher

Publications and source records attributed to R W Fisher.

7 recordsLinked to original sources
PubMed1979

Reversal by Light of Ethylene-induced Inhibition of Spore Germination in the Sensitive Fern Onoclea sensibilis: An Action Spectrum.

Spores of the fern Onoclea sensibilis L. normally germinate to produce two cells of unequal size. The larger cell divides to produce the familiar heart-shaped prothallus. The smaller cell elongates and differentiates into the rhizoid but normally does not divide again. Onoclea spores germinate in complete darkness. Dark germination can be completely inhibited by ethylene gas (10 microliters per liter is saturating). This inhibition can be reversed by light. Broad band colored light studies were designed to determine which area of the spectrum was most effective in overcoming ethylene inhibition. White light treatment resulted in 17% germination. Blue light treatment resulted in 1% germination. Red light treatment resulted in 15% germination. Red light, therefore, was most effective and accounted for most of the effects of white light. A detailed action spectrum was constructed using narrow band interference filters in the wavelength range from 350 to 764 nanometers. The action spectrum has only one major peak at 711 nanometers.

Journal Article↗
PubMed1978

Examination and evaluation of germination and protonemal development for Onoclea sensibilis fern spores treated with aflatoxin B1.

Experiments were designed to test the effects of aflatoxin B1 (AFB1) on germination and subsequent development of the gametophytes of the sensitive fern Onoclea sensibilis. AFB1 concentrations used were 0, 2.5, 5.0, 7.5, 10.0 and 12.5 muM. Preliminary studies indicated that, under all AFB1 concentrations tested, germination was maximum after 144 hrs. Additional studies revealed that during this time period protonemal growth was in the log phase. Percent germination was inhibited by increasing concentrations of AFB1; A 50% inhibition was noted at 12.5 muM. In addition, increasing concentrations of AFB1 caused a reduction in the total number of cells per protonema. Preliminary analysis indicated that this was caused by a reduction of the rate of cell production rather than total inhibition of cell division. A comparison of the dose-response curves for both of the above effects demonstrated that sensitivity to AFB1 starts at 2.5 muM. This may indicate that AFB1 is acting on a process common to both phenomena. The fern spore germination system could be a "simple" model system in which to study the site and mode of action of AFB1.

Aflatoxins↗
PubMed1978

Lateral diffusion of the phospholipid molecule in dipalmitoylphosphatidylcholine bilayers. An investigation using nuclear spin--lattice relaxation in the rotating frame.

Measurements of the proton NMR spin--lattice relaxation time in the rotating frame (T 1rho) have permitted the explicit determination of the lateral diffusion coefficient of phospholipid molecules in the lamellar mesophase of dipalmitoylphosphatidylcholine at temperatures above the phase-transition temperature. The experimentally observed temperature and frequency dependence of T 1rho for the dipalmitoylphosphatidylcholine protons suggest that intermolecular dipole--dipole relaxation contributions are important. Proton T 1rho experiments involving dilution with deuterated dipalmitoylphosphatidylcholine support the premise that intermolecular dipolar interactions are significant and, concomitantly, that lateral diffusion is the motion modulating that interaction. The lateral diffusion coefficient is determined directly from the dependence of the rotating frame spin--lattice relaxation rate (1/T 1rho) on the strength of the applied radiofrequency field in the spin-locking experiment. A series of experiments with varying concentrations of dipalmitoylphosphatidylcholine in the lamellar mesophase indicates that the lateral diffusion coefficient varies as a function of phospholipid concentration.

Chemical Phenomena↗