HOEKSTRA, F.A.; Wageningen University: Differential longevities in desiccated anhydrobiotic plant systems

Desiccation tolerance is a wide-spread phenomenon in the plant kingdom, particularly in small propagules lacking an own root or rhizome system, such as seeds, pollen, spores of spore plants, and whole Bryophytes, but rare in whole, vascular plants. However, longevities in the desiccated state vary considerably – from a few days in some pollen types to many decades in some seeds and moss spores, vegetative tissues being intermediate in that respect. Particularly moss spores are long-lived, which indicates that small size does not appear to be a factor limiting life span. The formation of a glassy state in the cytoplasm upon water loss considerably increases viscosity and slows deteriorative chemical reactions. Therefore, ageing is relatively faster above the glass transition temperature (Tg) than below. However, the presence of a glassy state cannot explain the large differences in life span among desiccation-tolerant systems. Fourier transform infrared spectroscopy can give insight in the hydrogen bonding strength of the glass forming compounds. Small sugars have a relatively low Tg and strong hydrogen bonding interactions, whereas large sugars have a relatively high Tg and weak hydrogen bonding interactions. Proteins and some small metabolites increase both hydrogen bonding strength and Tg of sugar glasses. The correlation between hydrogen bonding strength in the cytoplasmic glass and life span will be exemplified in developmentally defective mutant seeds of Arabidopsis and in propagules from different phyla. We propose that the formation of a molecularly dense glassy state of high Tg may be paramount for an extended life span at low water content.