Partial dehydration and ABA induce tolerance to desiccation-induced ion leakage in the moss Atrichum androgynum

A simple ion leakage assay was used to test if specific hardening treatment s can increase desiccation tolerance in the moss Atrichum androgynum. Reduc ing the relative water content (RWC) of apical stem segments to c. 0.6 for 3 d, followed by storing the material fully hydrated for 1 d typically redu ced the proportion of intracellular K+ lost following desiccation by betwee n 15 and 20% compared with controls kept moist. Reducing the RWC of the pla nts further during hardening by using air of lower humidities during harden ing did not further increase tolerance. An optimal increase in tolerance oc curred after 3 d of hardening; no further increase in tolerance occurred by extending the hardening period to 5 d. While heat shock had no effect, tre ating the moss with abscisic acid (ABA) for 1 h followed by storage for 3 d in the light increased resistance to ion leakage to the same extent as par tial dehydration. The ABA-induced increase in tolerance was much less if pl ants were pre-treated in the dark, and could be abolished by simultaneously treating the moss with the protein synthesis inhibitor cyclohexamide. Resu lts indicated that A. androgynum possesses inducible tolerance mechanisms t hat reduce desiccation-induced damage.