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 stress and fully recover during periods of water availability. Rehydration from the air-dry state occurred rapidly (within 24 h) with a concurrent initiation of protein synthesis. A low-molecular-weight doublet was synthesized during water stress and was stable for at least 24 h after rehydration. These proteins were expressed also when the fully hydrated fronds were subjected to exogenous ABA even though drying resulted in a 10-fold reduction in ABA content. The large subunit of Rubisco was synthesized during drying, but despite temporary accumulation, the de novo synthesized component was degraded during rehydration. During rehydration from the air-dry state, unique rehydration-specific polypeptides were produced. These polypeptides were synthesized at different water contents and times of rehydration, and were transiently expressed. This transient expression may mean that they are only necessary during the early stages of rehydration when the rapid initiation of physiological and repair processes is essential. The response of this fem to desiccation has features which are similar to those reported for desiccation-tolerant mosses, and others which are reminiscent of desiccation-tolerant angiosperms.