Ecologymechanism

Desiccation tolerance

Drying out does not make a cell thirsty. It makes it collapse — because water was holding the shapes, and something has to take its place.

The danger in drying out is not thirst — it is structural. Water holds membranes and proteins in shape, and when it leaves they collapse. Organisms that survive drying replace water’s structural role with sugars or proteins that set into a glass.

The intuitive picture of drying out is of an organism running out of something it needs, like fuel. That is not what happens, and getting it wrong makes the solutions look arbitrary. Water in a cell is not only a solvent; it is a structural component. A membrane is held in its layered arrangement partly by water at its surface, and a folded protein is held folded partly by water bonding to its outside. Take the water away and the membrane’s packing changes, sometimes irreversibly, and proteins unfold and stick to each other. The organism is not thirsty. It is coming apart. Once that is the problem, the solutions make sense: they are substitutes. Certain sugars, trehalose most famously, can hydrogen-bond to membranes and proteins in the places water was occupying, holding the shapes while the water goes. Tardigrades, which accumulate little or no trehalose, use a family of unusually shapeless proteins instead — proteins with no fixed structure of their own, which is exactly what lets them pack around other molecules and set. In both cases the endpoint is the same: the cell contents become a glass rather than a crystal or a soup, and everything is held still. There is one piece of evidence here that is rarer than it sounds. Most survival mechanisms are supported by correlation — the tolerant animal has the substance. The tardigrade proteins were tested by putting them into yeast and bacteria, which cannot survive drying, and those organisms then could. That is sufficiency, and it is a much stronger form of evidence than presence.

Developed coverage · 55% complete · reviewed 2026-09-03

What this page covers

Found in tardigrades, rotifers, nematodes, brine shrimp, some insects, many mosses and lichens, resurrection plants, nearly all seeds, and numerous yeasts and bacteria. The mechanism is broadly shared even where the protective molecules differ.

Often confused with: Drought resistance in plants, which usually means avoiding water loss rather than surviving it; Being waterproof, which is the opposite strategy; Simply not needing much water, which is a matter of degree and not of kind

The real danger: Structural collapse of membranes and proteins, not lack of water as a supply
The solution: Sugars or disordered proteins that occupy water’s place and vitrify
The strong evidence: Tardigrade proteins transferred into yeast and bacteria confer tolerance they lacked
What still kills a tolerant organism: Drying too fast, or rehydrating too fast

What actually goes wrong when a cell dries

Not a shortage. A collapse.

The danger in drying out is not thirst. Water holds membranes and proteins in shape, and when it leaves they collapse. Organisms that survive it fill the gap with sugars or proteins that set into a glass.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Desiccation tolerance depends on replacing the structural and hydrogen-bonding role of water at membrane and protein surfaces, and on vitrification of the cytoplasm into an amorphous glass that arrests molecular mobility. Protectants include disaccharides such as trehalose and, in tardigrades, intrinsically disordered proteins.

Who this applies to: Documented in desiccation-tolerant animals, plant seeds, resurrection plants, yeasts and bacteria.
Studied in: Tardigrada, Rotifera, Nematoda, Artemia franciscana, Plantae

Why we rate it this way, and what the caveats are

EstablishedHigh confidence

Supported by biophysical measurement, by the correlation between protectant and tolerance, and — unusually — by sufficiency: transferring tardigrade proteins into yeast and bacteria makes them survive drying.

How far it can be extended

The biophysical mechanism has been demonstrated in animals, plants and microbes independently, and protectants transplanted between them confer tolerance.

Caveats

The protectants differ by group: trehalose dominates in brine shrimp and yeast, disordered proteins in tardigrades, and both plus others in plants.
Vitrification is necessary but not sufficient — the drying rate matters, and animals dried too fast die whatever they contain.

Still unanswered

How the disordered proteins are held ready and what triggers their production quickly enough as drying begins.
Why some individuals of a tolerant species survive a drying that kills their neighbours.

Last reviewed 2026-09-03

The evidence (3 studies)

Supports · primary
Anhydrobiosis
Crowe et al., 1992 · Annual Review of Physiology
The biophysics of water replacement and vitrification.
Supports · primary
Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation
Boothby et al., 2017 · Molecular Cell
Sufficiency, not correlation: expressing the proteins in organisms that lack them confers tolerance.
Supports · supporting
The biology of tardigrade disordered proteins in extreme stress tolerance
Hesgrove and Boothby, 2020 · Cell Communication and Signaling
Establishes that several protein families contribute and no single molecule accounts for tolerance.

The short answer

Why does drying out kill a cell?

Because water is holding structures in shape. Membranes are kept in their layered packing and proteins in their folds partly by water at their surfaces, and removing it lets both come apart — often irreversibly.

This is why the solutions are substitutes rather than reservoirs. Nothing about desiccation tolerance involves storing extra water; the organisms that do it best lose almost all of theirs. What they have instead are molecules that can sit where water sat and make the same bonds. The reframing also explains a detail that otherwise looks arbitrary: why drying too fast is lethal to an organism that would survive drying slowly. The protective molecules have to be made and distributed, and the glass has to form, and both of those take time the fast-dried organism does not get.

Check it for yourself

Diagram

What drying does to a membrane, with and without protection

The danger is structural collapse, not a shortage.

The same explanation in words

Three panels of the same membrane. Wet: two straight parallel layers with water molecules between them holding the spacing. Dried and unprotected: the layers have buckled into irregular waves, the packing collapsed, often irreversibly. Dried and protected: the layers are straight again, with sugar or protein molecules occupying the positions water held, and the whole cell content set into a glass. In that glass molecules cannot move, so nothing degrades — which is why the state lasts years, and why drying too fast still kills, because the glass has no time to form.

Presence, correlation, sufficiency

Most survival mechanisms are supported by the weakest of these. This one has the strongest.

There is a hierarchy of evidence in mechanism biology that is worth naming, because extreme-survival writing rarely distinguishes its levels. The weakest is presence: the tolerant organism contains the substance. Better is correlation: organisms or stages with more of it survive better. Better still is necessity: remove it and tolerance goes. Strongest is sufficiency: put it into something that lacks the ability, and the ability appears. Desiccation tolerance is one of the few places in this whole subject where the top of that hierarchy has been reached.

How strong the evidence is, and what each level does and does not show

Level of evidence	What was done	What it establishes
Presence	The substance is found in a tolerant organism	Very little — tolerant organisms contain thousands of substances
Correlation	More of it goes with better survival	It is involved, or tracks something that is
Necessity	Removing it removes tolerance	It is required, though not that it is the whole story
Sufficiency	Adding it to a non-tolerant organism confers tolerance	It can do the job on its own, in that context

Expressing tardigrade disordered proteins in yeast and in bacteria — neither of which survives drying — makes them survive it. That is sufficiency, which almost nothing else in extreme-survival biology has demonstrated.

Based on The danger in drying out is not thirst. Water holds membranes and proteins in shape, and when it leaves they collapse. Organisms that survive it fill the gap with sugars or proteins that set into a glass.

Sufficiency in yeast still does not mean these proteins are the whole story in the tardigrade. Several protein families contribute, they are not interchangeable, and the full account is not written. The strength of the evidence is about what the proteins can do, not about how much of the animal’s tolerance they explain.

How we know

Moving the mechanism into an organism that lacked it

Tardigrades contain unusual proteins when they dry. Are those proteins doing the protecting, or merely present in an animal that protects itself some other way?

Genes upregulated in tardigrades during drying were identified, and the intrinsically disordered proteins they encode were expressed in yeast and in bacteria — organisms that do not survive desiccation. The recipients were then dried and their survival compared against the same organisms without the transferred proteins.

What happened

Yeast and bacteria expressing the tardigrade proteins survived drying that they otherwise do not survive. The proteins were shown to vitrify — to set into a glass — on drying.

What it shows

Sufficiency, which is rare in this field. Almost every survival mechanism in extreme-survival biology is supported by presence or correlation: the tolerant animal contains the substance. Putting the substance into something that lacks the ability and watching the ability appear is a categorically stronger result.

What it does not show

It does not show that these proteins are the whole story in the tardigrade itself. Several protein families contribute, they are not interchangeable, and tolerance in the animal is multi-mechanism and only partly understood. Sufficiency in yeast establishes what the proteins can do, not how much of the animal’s tolerance they account for.

The controls — what makes this evidence rather than a story

The same yeast and bacterial strains without the tardigrade proteins, dried identically.
Comparison against trehalose, the sugar that other desiccation-tolerant organisms rely on and that tardigrades accumulate at low levels or not at all.
Multiple protein families tested rather than one, so that a single fortunate candidate would be distinguishable from a general effect.

From Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation

Who does it, and what they have in common

Independently evolved in animals, plants, fungi and bacteria — with different molecules and the same endpoint.

Tardigrades, rotifers and nematodes — small animals of films of water, which dry out whenever their habitat does, which is often.
Brine shrimp cysts, which are among the most studied desiccation-tolerant objects in biology and rely heavily on trehalose.
Seeds, where the tolerance is so routine that it is easy to forget it is remarkable: most seeds are dried organisms waiting.
Mosses, lichens and resurrection plants, which dry to apparent death and green within hours of rain.
Yeasts and many bacteria, which is why the tardigrade protein transfer experiment had somewhere to go.

The pattern across that list is habitat rather than kinship. These organisms are not related; they share the situation of living in places that dry out predictably and unavoidably, and being too small or too fixed to leave. Where an animal can walk away from a drying puddle, it does. Where it cannot, this is the alternative.

Cryptobiosis
The state drying produces, and what can be said about it
Tardigrades
The animal where the mechanism is best understood
Lichen
Drying and reviving as an ordinary weekly event

The research behind this page

8 studies, newest first. Each one has a page explaining what it found and what it could not show.

2020Cell Communication and Signaling

The biology of tardigrade disordered proteins in extreme stress tolerance

Several distinct protein families contribute, they are not interchangeable, and no single one accounts for tardigrade tolerance; the mechanisms are only partly understood.

2017Molecular Cell

Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation

Tardigrade-specific intrinsically disordered proteins are strongly induced by drying.

2011Current Opinion in Plant Biology

Programming desiccation-tolerance: from plants to seeds to resurrection plants

Resurrection plants use the same protective repertoire as seeds — sugars, late embryogenesis abundant proteins, antioxidant systems — with the additional problem, unique to green tissue, of shutting down photosynthesis safely so that a drying leaf in sunlight does not destroy itself.

2001Comparative Biochemistry and Physiology Part B

Cryptobiosis — a peculiar state of biological organization

In the deepest cryptobiotic states no metabolism can be measured by available methods, and the organism’s survival depends on the physical preservation of its structures rather than on any ongoing repair.

2000Plant Ecology

The evolution of vegetative desiccation tolerance in land plants

Vegetative desiccation tolerance was probably present in the earliest land plants and retained in mosses, but in flowering plants it appears to have been re-evolved independently several times, most likely by redeploying the tolerance programme that seeds already use.

1992Annual Review of Physiology

Anhydrobiosis

Organisms that survive drying accumulate protective sugars that substitute for water at membrane and protein surfaces and hold the cell contents in a glass, preventing the structural collapse that otherwise occurs as water leaves.

1971Science

Desiccation-tolerant flowering plants in southern Africa

A substantial number of flowering plant species survive the drying of their leaves to air-dryness and recover full function within hours to days of rewetting — a capacity previously thought largely confined to mosses and lichens.

1959Proceedings of the Royal Society of London B

The problem of anabiosis or latent life: history and current concept

There exists a genuine state in which no metabolic activity can be measured and the organism nonetheless revives, and it is distinct from a merely very low metabolic rate.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 55% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 5 claims and answers 0 mapped search questions.

no popular claim about this subject has been checked yet
Plant desiccation tolerance — seeds and resurrection plants — is listed rather than treated in its own right.
How organisms sense that drying has begun, early enough to prepare, is not covered.
The damage that accumulates during long dry storage is unresolved and only raised as a question.