Desiccation tolerance.

Desiccation tolerance is the ability to survive loss of 90% of cellular water or dehydration to tissue water concentrations of ≤0.1 g H2O.g-1 dry mass. It is relatively common in reproductive structures such as seeds (termed orthodox), but is rare in vegetative tissues, occurring in some 135 angiosperm species (termed resurrection plants). In this chapter we present an overview of the stresses associated with desiccation and review the current mechanisms proposed to explain how orthodox seeds and resurrection plants tolerate such water loss. Physiological, biochemical and molecular processes involved in protection from mechanical stress, oxidative damage and metabolic disruptions are discussed and similarities between seeds and resurrection plants are drawn. Protective mechanisms unique to vegetative tissues are presented and differences among species are discussed. We review the biogeographical distribution and evolution of angiosperm resurrection plants and propose that the developmentally regulated programme of acquisition of desiccation tolerance in seeds is utilized in the acquisition of tolerance in vegetative tissues of resurrection plants, possibly in response to environmentally regulated rather than developmental cues.