Long-term stability of protein secondary structure in dry seeds

Changes in protein secondary structure during seed aging were studied by in situ Fourier transform infrared microspectroscopy. Seeds of onion, white cabbage and radish, harvested in 1969, were stored at 15-20 degrees C and 30% relative humidity. Fresh control seeds were harvested in 1994 and stored under the same conditions. In 1995, the germination capacity of seeds was,90% for the 1994 hanrest and zero for the 1969 harvest. Inspection of the amide-I bands in Fourier self-deconvolved infrared spectra of thin slices of embryo axes of the various seeds did not reveal major changes in relative peak height and band position of the different protein secondary structures with aging. No protein aggregation and denaturation were found after long-term storage. Heating of dry viable radish seeds up to 145 degrees C did not cause appreciable protein denaturation. In contrast, boiling hydrated radish seeds for 5 min led to decoiling of the alpha-helical structure and the appearance of a band at 1627 cm(-1). This band is characteristic of intermolecular extended beta-sheet structures. We conclude that, despite the loss of viability- and the long postmortem storage period, secondary structure of proteins in desiccation tolerant dry seed is very stable and conserved during several decades of open storage. (C) 1991 Elsevier Science Inc.