CHARACTERIZATION OF PROTEIN SYNTHETIC CHANGES IN A DESICCATION-TOLERANT FERN, POLYPODIUM-VIRGINIANUM - COMPARISON OF THE EFFECTS OF DRYING,REHYDRATION AND ABSCISIC-ACID

The desiccation-tolerant fem, Polypodium virginianum, was able to lose more than 60% of its fresh weight during periods of prolonged water s tress and fully recover during periods of water availability. Rehydrat ion from the air-dry state occurred rapidly (within 24 h) with a concu rrent initiation of protein synthesis. A low-molecular-weight doublet was synthesized during water stress and was stable for at least 24 h a fter rehydration. These proteins were expressed also when the fully hy drated fronds were subjected to exogenous ABA even though drying resul ted in a 10-fold reduction in ABA content. The large subunit of Rubisc o was synthesized during drying, but despite temporary accumulation, t he de novo synthesized component was degraded during rehydration. Duri ng rehydration from the air-dry state, unique rehydration-specific pol ypeptides were produced. These polypeptides were synthesized at differ ent water contents and times of rehydration, and were transiently expr essed. This transient expression may mean that they are only necessary during the early stages of rehydration when the rapid initiation of p hysiological and repair processes is essential. The response of this f em to desiccation has features which are similar to those reported for desiccation-tolerant mosses, and others which are reminiscent of desi ccation-tolerant angiosperms.