Friday Fabulous Fern - A botanical resurrection

Any tourist to Florence Italy will get their fill of resurrection because of the abundance of religious-themed art.  But there’s another kind of resurrection that is very common in these parts; so called “resurrection” plants or desiccation tolerant plants.  Many ferns, clubmosses, mosses, and leafy liverworts are capable of desiccation and rehydration, sometimes quite rapidly.  In this part of Tuscany, the agricultural and urban landscape is composed of wall after wall after wall of mostly rough limestone blocks. There’s a lot of surface area there for tough plants who can hang onto the wall by rooting into the cracks and crevasses between or in the rocks. Such environments are pretty harsh, very hot and dry, intermittently hospitable after rains or during a rainy season. Quite a number of these desiccation tolerant plants can be found on the walls of this estate.  The primary fern is Asplenium ceterach, the rusty-backed fern, so called because the backs of the leaves are covered with brown, scaly hairs that hide the sori. As the fern dries out the pinnae (leaflets) and fronds curl such that the brown back side of the leaves is exposed, and the fronds curl almost into a reverse fiddlehead. The hairiness helps reduce water loss, perhaps reflects sunlight, and may speed rehydration by trapping water in capillary spaces. When dehydrated these ferns seem like real crispy critters.  Right now a little demonstration is underway to see how fast some of these desiccated ferns can rehydrate.  As expected some of the mosses are very fast at this indeed. But within minutes the fronds begin to uncurl. 12 hours later the fern was rehydrated looking green and fresh. The non-botanists were quite impressed partly because the transformation is so striking, and partly because people have this idea that ferns are delicate little things.

A real resurrection (fern)

Is there a plant grower anywhere who has never accidentally let a plant dry out and die? Doh! Dehydration is such an annoyance. Yet there are a number of organisms that can dry out and survive quite well. Slime molds and yeasts can be dehydrated and survive for months. Some mosses and leafy liverworts can dehydrate, and rehydrate, on a daily basis, and sometimes for even longer periods of time. But when you get to vascular plants the ability to survive dehydration becomes rare perhaps because the whole idea of vascular tissue, cuticle, and stomata is to maintain a hydrated state, as long as the roots can replace the water being continually lost through transpiration. Of course comparing vascular plants to mosses and liverworts is not fair because the former are diploids and the latter haploids (explanatory link). But the point is that among vascular plants the ability to dehydrate and survive is rare, and no matter what, no one really seems to understand how even a slime mold can dehydrate into a brittle piece of yellow cytoplasm and then blob itself back to life when water is added.
One exception among vascular plants is the resurrection fern, Polypodium polypodioides. Sometimes they are sold as novelty items; just add water and the brittle fern rehydrates and greens up (see image). Cool. A recent report suggests that this ability is linked to appropriately named proteins called dehydrins, which appear to prevent cell wall damage from the “wrinkling up” that occurs when cells dry out. Could such a gene be used to engineer drought resistant crops? Maybe. And this is another example of why the powers that be, and that includes all of the people holding the purse strings, should encourage, rather than discourage, biologists to study a diversity of organisms. You can just imagine the derision a grant proposal would get from the USDA if you said you were going to study a cute little fern. Sure kid, how nice, now if you want money from us study corn, which never, ever suffers from droughts.