Unifying perspectives of some mechanisms basic to desiccation tolerance across life forms

Desiccation-tolerant organisms, or life-cycle stages of particular taxa, occur among animals, higher and lower plants, terrestrial micro-algae, lichens and bacteria. Recent investigations have revealed that a number of mechanisms conferring desiccation tolerance appear to be common to the diversity of life forms able to survive extreme dehydration. In particular, parallel processes involving late embryogenic abundant (LEA) or LEA-like proteins, accumulation of sugars, aspects of active oxygen species (AOS) and non-enzymic and enzymic antioxidants have been the recent focus of attention, some across a diversity of organisms. The present contribution considers advances made from the study of these processes, particularly in enhancing current understanding of the composition of, and protection afforded by, the glassy state in desiccated organisms. Strong evidence that proteins, particularly LEAs, are implicated in glass formation is reviewed, and behaviour of such proteins upon dehydration is discussed in this context. The question of the ability of cells to survive complete water removal is considered in the context that it is unlikely, and that the basis of the deterioration of very dry seeds results from abstraction of water necessary to maintain the integrity of the intracellular glassy state. Finally, the revelation that desiccated seeds deteriorate with time, even under extremely good genebanking conditions, is discussed.