Properties of proteins and the glassy matrix in maturation‐defective mutant seeds of Arabidopsis thaliana

SummaryIn situFourier transform infrared microspectroscopy was used to study the heat stability of proteins and hydrogen bonding interactions in dry maturation‐defective mutant seeds ofArabidopsis thaliana. α‐Helical, turn and β‐sheet conformations were the major protein secondary structures in all of these seeds. On heating, intermolecular extended β‐sheet structures, typical of protein denaturation, were formed in abscisic acid‐insensitive (abi3) and leafy cotyledon (lec) mutant seeds. Proteins in dry wild‐type seeds did not denature up to 150°C, but those in dry desiccation‐sensitive,lec1–1,lec1–3andabi3–5seeds did at 68, 89 and 87°C, respectively. In the desiccation‐tolerantabi3–7andabi3–1seeds, denaturation commenced above 120 and 135°C, respectively. Seeds of theaba1–1 abi3–1double mutant showed signs of denaturation already upon drying. The molecular packing in the seeds was studied by observing the shift in the position of the OH‐stretching vibration band with temperature. The maximal rate of change of this band with temperature was much higher in the desiccation‐sensitiveabi3–5,aba1–1 abi3–1,lec1–1, andlec1–3mutant seeds than in the desiccation‐tolerant wild‐type,abi3–1,abi3–7, andlec2–1seeds. We interpret this to mean that the molecular packing density is higher in dry desiccation‐tolerant than in dry desiccation‐sensitive seeds, which is associated with a higher or lower protein denaturation temperature, respectively. The results are discussed in relation to the physiological and biochemical characteristics of these mutant seeds.