What makes desiccation tolerable?

It is no small feat for an organism, after losing more than 90% of its cellular water, to live and continue growing after rehydration. Many plants, one might argue, perform this trick when seeds develop; the topic here, however, is not seed maturation, dormancy and successful germination, but tolerance to extreme desiccation in the vegetative state. This involves, for example, the often rapid, non-destructive drying of existing leaves and their survival after water is returned. The ability to withstand such water loss is common to many algae and lichens, and is also found in liverworts, mosses, fern-like species and some ferns. The ability is missing entirely from gymnosperms but appears again in a few angiosperms. Oliver, Tuba and Mishler cover extremist strategies for survival under water deficit in a recent article [1] entitled 'The evolution of desiccation tolerance in land plants'. Their discussion offers an evolutionary view, outlines different strategies of tolerance acquisition, introduces emerging molecular genetic components, and finally outlines future work with a focus on genomic analyses. Knowing, it is argued, the genetic and biochemical makeup that brings about tolerance to vegetative desiccation might provide strategies to engineer protection of plants under less severe conditions.When the precursors of higher plants first appeared on land - species without any water-conducting organs - desiccation stress became a possibility and a threat. Descendants of the early colonizers, the liverworts, hornworts and mosses (bryophytes), display implicitly primitive tolerance mechanisms by being 'always prepared'. They constitutively express proteins, which, while not totally protecting existing tissues from damage during drying, minimize damage by a focus on the repair of cell structures during the rehydration phase. Repair capacity is stored in ribonucleoprotein particles (RNPs). Three foundations for survival are brought out by Oliver et al.: the first is to