ABA-induced tolerance to ion leakage during rehydration following desiccation in the moss Atrichum androgynum

A simple ion leakage assay was used to investigate the effect of abscisic acid (ABA) pretreatment on desiccation tolerance in the moss Atrichum androgynum. Results from experiments involving the application of the protein synthesis inhibitor cyclohexamide during desiccation or rehydration suggested that pretreatment with ABA does not facilitate the production of "protection" or "repair" proteins during desiccation or rehydration. Rather, ABA induces the synthesis of these proteins during pretreatment. The ABA-induced increase in tolerance was much less if plants were pretreated in the dark. Exposure to red light could not substitute for white light, suggesting that ABA action does not require phytochrome. Desiccating intact long stem segments or long segments separated into apical and basal parts had no effect on the desiccation tolerance of either plant part. This suggests that no movement of signals or protective molecules occurs from the stem bases to the apices during desiccation. Basal stem segments were much more sensitive to desiccation than apical regions, suggesting during senescence a breakdown in mechanisms that protect mosses from injury occurs. The implications of these findings for the water relations of A. androgynum are discussed.