INFLUENCE OF WATER-CONTENT AND TEMPERATURE ON MOLECULAR MOBILITY AND INTRACELLULAR GLASSES IN SEEDS AND POLLEN

Although the occurrence of intracellular glasses in seeds and pollen h as been established, physical properties such as rotational correlatio n times and viscosity have not been studied extensively. Using electro n paramagnetic resonance spectroscopy, we examined changes in the mole cular mobility of the hydrophilic nitroxide spin probe 3-carboxy-proxy l during melting of intracellular glasses in axes of pea (Pisum sativu m L.) seeds and cattail (Typha latifolia L.) pollen. The rotational co rrelation time of the spin probe in intracellular glasses of both orga nisms was approximately 10(-3) s. Using the distance between the outer extrema of the electron paramagnetic resonance spectrum (2A(ZZ)) as a measure of molecular mobility, we found a sharp increase in mobility at a definite temperature during heating. This temperature increased w ith decreasing water content of the samples. Differential scanning cal orimetry data on these samples indicated that this sharp increase corr esponded to melting of the glassy matrix. Molecular mobility was found to be inversely correlated with storage stability. With decreasing wa ter content, the molecular mobility reached a minimum, and increased a gain at very low water content. Minimum mobility and maximum storage s tability occurred at a similar water content. This correlation suggest s that storage stability might be at least partially controlled by mol ecular mobility. At low temperatures, when storage longevity cannot be determined on a realistic time scale, 2A(ZZ) measurements can provide an estimate of the optimum storage conditions.