An Overview of Mechanisms of Desiccation Tolerance in Selected Angiosperm Resurrection Plants

The vegetative tissues of resurrection plants, like seeds, can tolerate desiccation to 5% relative water content (RWC) for extended periods and yet resume full metabolic activity on re-watering. In this review we will illustrate how this is achieved in a variety of angiosperm resurrection plants, our studies ranging from the ecophysiological to the biochemical level. At the whole plant level, leaf folding and other anatomical changes serve to minimise light and mechanical stress associated with drying and rehydration. The mechanisms of cell wall folding are described for Craterostigma wilmsii and Myrothanmus flabellifolia. Free radicals, radical oxygen species (ROS) usually generated under water-deficit stress by photosynthesis, are minimised by either homoiochlorophylly (e.g. C. wilmsii and M. flabellifolia) or poikilochlorophylly (e.g. Xerophyta sp.). The antioxidant systems of these plants effectively deal with ROS generated by other metabolic processes. In addition to antioxidants common to most plants, resurrection plants also accumulate polyphenols such as 3, 4, 5 tri-O-galloylquinic acid in M. flabellifolia, and seed-associated antioxidants (e.g. 1-cys-peroxiredoxin and metallothionines) as effective ROS scavengers. Sucrose accumulates at low RWC, presumably protecting the sub-cellular milieu against desiccation-induced macromolecular denaturation. _____________________________________________________________________________________________________________