The effect of drying rate on the survival of three desiccation-tolerant angiosperm species

The effect of drying rate on the survival of three angiosperra resurrection plants, Craterostigma wilmsii (homoiochlorophyllous), Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius (homoiochlorophyllous) was examined. All species survived slow drying, but only C. wilmsii was able to survive rapid drying. C. wilmsii was rapidly able to induce protection mechanisms such as folding of cell walls to prevent mechanical stress and curling of leaves to minimize light stress, and thus survived fast drying. Rapid drying of X. humilis and M. flabellifolius appeared to allow insufficient time for complete induction of protection mechanisms. In X. humilis, there was incomplete replacement of water in vacuoles, the photosynthetic apparatus was not dismantled, plasma membrane disruption occurred and quantum efficiency of photosystem II (F-V/F-M) did not recover on rehydration. Rapidly dried leaves of M. flabellifolius did not fold tightly against the stem and F-V/F-M did not recover. Ultrastructural studies showed that subcellular damage incurred during drying was exacerbated on rehydration. The three species co-occur in environments in which they experience high desiccation pressures. C. wilmsii has few features to retard water loss and thus the ability for rapid induction of subcellular protection is vital to survival. X. humilis and M. flabellifolius are able to retard water loss and protection is acquired relatively slowly. (C) 1999 Annals of Botany Company.