Revival of respiration and photosynthesis in dried leaves of Polypodium polypodioides

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Abstract
The leaves of the epiphytic fern Polypodium polypodioides, which lives on the branches of trees, are very similar to those of most higher plants except for the presence of scales on the dorsal side of the leaves. The structure of the cells of the chloroplasts and the mitochondria is the same as that of other higher plants. The only obvious difference found was that the contents of the central vacuole solidified when dehydrated. P. polypodioides was not damaged by loss of 97% of its normal water content and photosynthetic activity was found to be proportional to water content between 20 and 100% water content. When a dried leaf was immersed in liquid water, almost all of the original photosynthetic activity reappeared in the first 30 min of rehydration, provided incisions had been made into the leaf before drying. The rate of water uptake by intact (uncut) leaves was strongly inhibited by anaerobic conditions. This inhibition could be relieved by cutting the leaves, by supplying oxygen, or by removing the scales. Since in P. polypodioides the photosynthetic apparatus is not damaged by severe dehydration its quick revival does not depend on a special repair mechanism. Therefore, P. polypodioides should be a suitable object for a number of studies on the mechanism of photosynthesis.