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 (p oikilochlorophyllous) and Myrothamnus flabellifolius (homoiochlorophyllous) was examined. All species survived slow drying, but only C. wilmsii was ab le to survive rapid drying. C. wilmsii was rapidly able to induce protectio n 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 insuffi cient time for complete induction of protection mechanisms. In X. humilis, there was incomplete replacement of water in vacuoles, the photosynthetic a pparatus was not dismantled, plasma membrane disruption occurred and quantu m efficiency of photosystem II (F-V/F-M) did not recover on rehydration. Ra pidly dried leaves of M. flabellifolius did not fold tightly against the st em and F-V/F-M did not recover. Ultrastructural studies showed that subcell ular damage incurred during drying was exacerbated on rehydration. The thre e species co-occur in environments in which they experience high desiccatio n 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 protect ion is acquired relatively slowly. (C) 1999 Annals of Botany Company.