Characterization of Intracellular Glasses in Bean Axes with Relevance to Storage Stability

Abstract

Although evidence indicates that water in seed tissues exhibits glass properties, the physiological role of glasses in storage stability is still conjectural. We believe that this shortcoming is due to our lack of understanding the implications of the glassy state. Using differential scanning calorimetry we studied the thermal behaviours of glass transitions in axes of bean at temperatures between -120°C and +120°C. Three types of thermal behaviours associated with the glass transition were observed in tissues with water contents between 0.03 and 0.45 g H₂O/g DW. The appearance, the temperature and the amount of energy released during these transitions were dependent on the tissue water content. Below 0.03 and above 0.45 g H₂0/g DW, no glass transitions were observed. Because water content influences the glass—liquid transition behaviour, a Tg/water content curve is not entirely satisfactory to describe the glassy state of water in dry seeds. We present evidence that the non-equilibrium nature of glasses, the thermal history during glass formation and the complexity of molecular interactions between the glassforming solutes and water are important parameters to characterize the intracellular glass properties. These parameters are also relevant with seed storage stability.