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Characterization of Molecular Mobility in Seed Tissues: An Electron Paramagnetic Resonance Spin Probe Study

By Julia Buitink, Marcus A. Hemminga and Folkert A. Hoekstra

Abstract

AbstractThe relationship between molecular mobility (τR) of the polar spin probe 3-carboxy-proxyl and water content and temperature was established in pea axes by electron paramagnetic resonance (EPR) and saturation transfer EPR. At room temperature, τR increased during drying from 10−11 s at 2.0g water/g dry weight to 10−4 s in the dry state. At water contents below 0.07g water/g dry weight, τR remained constant upon further drying. At the glass transition temperature, τR was constant at ∼10−4 s for all water contents studied. Above Tg, isomobility lines were found that were approximately parallel to the Tg curve. The temperature dependence of τR at all water contents studied followed Arrhenius behavior, with a break at Tg. Above Tg the activation energy for rotational motion was ∼25kJ/mol compared to 10kJ/mol below Tg. The temperature dependence of τR could also be described by the WLF equation, using constants deviating considerably from the universal constants. The temperature effect on τR above Tg was much smaller in pea axes, as found previously for sugar and polymer glasses. Thus, although glasses are present in seeds, the melting of the glass by raising the temperature will cause only a moderate increase in molecular mobility in the cytoplasm as compared to a huge increase in amorphous sugars

Publisher: The Biophysical Society. Published by Elsevier Inc.
Year: 1999
DOI identifier: 10.1016/S0006-3495(99)77484-9
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