Anhydrous Biology & Glass Transitions

Abstract

The physical and chemical mechanisms by which anhydrobiotic organisms, such as plant seeds, pollen, bacteria, fungi, and others, tolerate extreme desiccation for long periods of time are still unknown. In desiccation intolerant organisms, dehydration causes irreversible events, such as disruption of cellular and intracellular membranes, denaturation of enzymes, and increase of solutes concentration, possibly with increased rates of destructive chemical reactions. We can assume that biological tolerance to dehydration will be achieved principally by adaptations in structural organization of cytoplasm and cytoplasmic components. We have examined the hypothesis that the cytoplasm of anhydrobiotic organisms exists in a glassy state even at physiological temperatures. A glassy state could represent an useful mechanism to trap residual water molecules and to prevent damaging interactions between cell components.1 In addition, the resulting highly viscous phase can be easily melted upon addition of water, thus restoring the possibility for metabolic activities. Preliminary evidence for the existence of a hydration-dependent glass-like transition at physiological temperatures occurring in the cytoplasm of maize seeds has been gained by calorimetric studies.2 Here we report on spin-probe electron paramagnetic resonance (EPR) measurements of cytoplasmic microviscosity and on thermal depolarization studies accomplished to detect the onset of a vitrified state in soybean seeds.