A Calorimetric Study of the Glass Transition Behaviors in Axes of Bean Seeds with Relevance to Storage Stability

Abstract

Although the presence of intracellular aqueous glasses has been established in seeds, their physiological role in storage stability is s t i l l conjectural. Therefore, we examined, using differential scanning calorimetry, the thermal behavior of glass transitions in axes of bean (Phaseolus vulgaris 1.) with water contents (WC) between O and 1 g H,O/g dry weight (g/g) and temperatures between -120 and +120°C. Three types of thermal behaviors associated with the glass transition were observed. The appearance, the glass + liquid transition temperature, and the amount of energy released during these transitions were dependent on the tissue WC. No glass transitions were observed at WC lower than 0.03 and higher than 0.45 g/g. A brief exposure to 100°C altered the glass properties of tissues with WC between 0.03 and 0.08 g/g but did not affect the thermal behavior of glasses with higher WC, demonstrating that thermal history is important t o the intracellular glass behavior at lower WC. Correspondence of data from bean to models predicting the effects of glass components on the glass --z liquid transition temperature suggests that the intracellular glasses are composed of a highly complex sugar matrix, in which sugar and water molecules interact together and influence the glass properties. Our data provide evidente that additional glass properties must be characterized to understand the implications of a glassy state in storage stability of seeds.Water and temperature play a significant and fundamental role in determining the storage longevity of orthodox seeds. Early models developed from storage experiments suggested that water and temperature were independent variables (Justice and Bass, 1978; Roberts and Ellis, 1989). However, theoretical considerations (Vertucci, 1992;Vertucci and Roos, 1993) and experimental data (Vertucci and Roos, 1993;Vertucci et al., 1994aVertucci et al., , 1994b have demonstrated that the effects of water and temperature on seed aging are interdependent. Conceptual models have been introduced to describe the interdependencies of WC and temperature on seed longevity. They rely on the findings that the nature and kinetics of degradative reactions in seeds change according to the physical properties of water

Conformation of a Group 2 Late Embryogenesis Abundant Protein from Soybean. Evidence of Poly (l-Proline)-type II Structure

“…BSA undergoes an irreversible thermal denaturation around 78°C as indicated by a high-temperature peak in the first scan and its disappearance in the second (Leprince and Vertucci, 1995). In contrast, DSC scans of rGmDHN1, purified with or without boiling treatment, showed no detectable high-temperature peak up to 100°C (Fig.…”

“…Thermal events were measured from 0°C to 100°C at a rate of 10°C min Ϫ1 using a differential scanning calorimeter (DSC-4 and DSC-7, PerkinElmer Instruments, Norwalk, CT) calibrated for temperature using methylene chloride (Ϫ95°C) and indium (156°C) standards and for energy with indium (28.54 J g Ϫ1 ) as previously described (Leprince and Vertucci, 1995). Helium gas was used for purging at a rate of 20 mL min Ϫ1 .…”

Temperature-Induced Extended Helix/Random Coil Transitions in a Group 1 Late Embryogenesis-Abundant Protein from Soybean

“…Thermal events were measured from 0°C to 100°C at a rate of 10°C min Ϫ1 using a Differential Scanning Calorimeter DSC-4 and DSC-7 (Perkin-Elmer, Norwalk, CT) calibrated for temperature using methylene chloride (Ϫ95°C) and indium (156°C) standards and for energy with indium (28.54 Jg Ϫ1 ) as previously described (Leprince and Vertucci, 1995). Helium gas was used for purging at a rate of 20 mL min Ϫ1 .…”

The Responses of Cytochrome Redox State and Energy Metabolism to Dehydration Support a Role for Cytoplasmic Viscosity in Desiccation Tolerance

“…Glass transitions were determined using Pyris-1 differential scanning calorimetry (PerkinElmer) using the settings described by Leprince and Walters-Vertucci (1995). The Tg was determined by the onset of the temperature range at which changes in specific heat, characteristic of a glass transition, occurred (Leprince and Walters-Vertucci, 1995).…”

“…These observations prompted us to examine further the interaction between O 2 diffusion as a function of WC and redox states of Cyts. Because of the physiological significance of glasses in seeds and pollen Leprince and Walters-Vertucci, 1995), we further assessed the relation between loss of water and increase in viscosity during drying. For this purpose, ESR spectroscopy was used to study the rotational motion of nitroxide spin-probes that were inserted into the cytoplasm.…”