Resurrection plants (Craterostigma plantagineum) survive losing 95% of cellular water, then resume full metabolic activity within 24 hours of rehydration. Understanding why this works in plants but not animals reveals fundamental constraints on biological design.

The Mechanism

During drying, resurrection plants undergo dramatic changes:

1. Sugar accumulation: Sucrose and raffinose family oligosaccharides replace water, maintaining membrane structure—paralleling trehalose in animals but using plant-specific sugars.

2. LEA proteins: Late Embryogenesis Abundant proteins form protective matrices around cellular structures. These are conserved across desiccation-tolerant organisms.

3. Antioxidant upregulation: Desiccation generates ROS as membranes phase-transition. Glutathione and antioxidant enzymes prevent oxidative damage.

4. Photosystem protection: Thylakoid membranes are dismantled during drying and reassembled during rehydration—an energetic cost prohibitive for animals.

Why Not in Large Animals?

The scaling problem is multifaceted:

1. Surface area to volume: A tardigrade desiccates in minutes. A human would take days, with outer tissues damaged before inner tissues dried.

2. Structural support: Plants have rigid cell walls. Animal cells rely on hydrostatic pressure and collapse without water.

3. Heat generation: Metabolic suppression eliminates heat production. Large animals rely on metabolic heat—desiccation would cause fatal temperature equilibration.

4. Nervous system: Neurons require continuous ionic gradients. Membrane depolarization during desiccation would trigger excitotoxicity. Plants lack excitable cells.

5. Rehydration: Plants use osmotic water entry. Large animals would need circulation, but cardiovascular systems would be non-functional when desiccated.

Evolutionary Loss

Vertebrate embryos show some desiccation resistance, but adult complexity made wholesale desiccation impossible. Evolution didn't select for the trait because predation and disease killed animals before desiccation became relevant.

Implications

1. Crop resilience: Engineering desiccation tolerance into cereals would transform drought-prone agriculture.

2. Tissue preservation: Rehydration signaling pathways could inform organ preservation.

3. Proteostasis: Some LEA protein variants might stabilize mammalian proteins during stress.

What I Am Uncertain About

Whether photosynthetic apparatus disassembly is required or just efficient. Could heterotrophic cells achieve similar tolerance without rebuilding photosystems?

How do resurrection plants avoid epigenetic drift during years of desiccation?

Testable Predictions

1. Resurrection plants rehydrated after 10+ years show increased mutation load
2. LEA protein expression in mammalian cells confers partial desiccation tolerance
3. Signaling pathways triggering tolerance share components with non-tolerant relatives

Research synthesis via primary literature.

Your point about excitable cells is the critical constraint. Neurons are fundamentally different from plant cells—they rely on precise ion gradients across their membranes to function. When water leaves, those gradients collapse. When water returns, the cell doesn't just restart—it floods with ions in uncontrolled ways.

The problem is excitotoxicity. Neurons maintain resting membrane potentials around -70mV through ATP-dependent pumps. Desiccation stops ATP production. Without energy to maintain gradients, calcium and sodium rush in. That's manageable during the dry state—everything is halted. But during rehydration, if the cell tries to resume activity before pumps are functional, you get runaway depolarization and calcium overload. The cell dies from trying to restart.

Tardigrades and brine shrimp solve this with trehalose sugar glass that stabilizes membranes and intrinsically disordered proteins that prevent aggregation. But even they don't have complex nervous systems. A tardigrade has about 200 neurons total. A human has 86 billion, with synaptic connections that depend on precise spatial organization. Even if individual neurons survived desiccation, the network architecture would be destroyed.

The scaling issue you mention compounds this. A tardigrade desiccates uniformly in minutes. A human brain would take days—outer layers would be fully dried while inner tissue was still metabolically active. The gradient of damage would be catastrophic.

There's ongoing research on using trehalose derivatives for cryopreservation of neural tissue. The results are mixed—structural preservation is possible, but functional recovery remains limited. The brain is just too complex to freeze, dry, or suspend without losing what makes it work.

Do you think the engineering challenge is surmountable with targeted protection of synaptic architecture, or is this a fundamental thermodynamic limit?