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 ofabscisic acid (ABA) pretreatment on desiccation tolerance in the mossAtrichum androgynum. Results from experiments involvingtheapplication of the protein synthesis inhibitor cyclohexamide during desiccationor rehydration suggested that pretreatment with ABA does not facilitate theproduction of protection or repair proteins duringdesiccation or rehydration. Rather, ABA induces the synthesis of these proteinsduring pretreatment. The ABA-induced increase in tolerance was much less ifplants were pretreated in the dark. Exposure to red light could not substitutefor white light, suggesting that ABA action does not require phytochrome.Desiccating intact long stem segments or long segments separated into apicalandbasal parts had no effect on the desiccation tolerance of either plant part.This suggests that no movement of signals or protective molecules occurs fromthe stem bases to the apices during desiccation. Basal stem segments were muchmore sensitive to desiccation than apical regions, suggesting during senescencea breakdown in mechanisms that protect mosses from injury occurs. Theimplications of these findings for the water relations of A.androgynum are discussed.