Dehydration

Christina Ramirez

Erek Dyskant

Why we need water?

• More than 2/3 of our weight

• Joints

• Temp regulation

• Regulates metabolic reactions

• Protein stability/folding and kinetics

How we lose water?

• Urine• Sweat• Vomiting• Diarrhea• Respiration

*How much urine do we output a day?*

*How much water do we take in? (in any form)

Water and electrolytes are lost

Our responses to dehydration

Plant Responses to Dehydration

Structural Plant Adaptations• Cacti

– Wide surface root systems• Many roots, towards surface of soil• Absorbs rain water very quickly, so it

can capture water from storms

– Accordion structure• Allows cacti to expand during wet

season, and contract droughts, preventing collapse and reducing exposed surface area.

– Thorns channel water to base of plant

Mesquite• Less water storage than cactus• Single very deep root.• Seasonal variation

– During hot/dry season• Loses leaves to conserve water• Chlorophyll concentration decreases,

slowing metabolism.

Cell Membrane

• Two bilayer phases– Liquid crystalline phase

– Gel Phase

Problems in membrane

• Low water potential

• Polar head group

no longer hydrated

• Van der Waals

• Tm

Rehydration

• Tm

– leaky membrane

• Disaccharides help!–

– Tm ?

Sucrose and Trehalose

• [solute] increases osmotic pressure

Crowe believes

• Water replacement theory

• Vitrification

Vitrification

• Ice

• Stabilize

• High viscosity

• Tm

• Reverses with the addition of water

• Tg solidviscous

What am I?

Active Dehydrated at high humidity

Low humidity Anesthetized

• Australian frogs borrow into mud as temporary ponds dry up, and can stay dormant for up to a year.

• Doesn’t remove waste• Urea content in muscles is 8 times that of

hydrated frogs– They may have hormones which are not

interrupted by urea, allowing them to maintain a higher urea concentration

– The urea buildup may serve as a mechanism to slow their metabolism

• Muscles don’t atrophy, as they do if the frog is anesthetized for the same amount of time

Frog Aestivation

Desiccation

• Complete loss of water, to equilibrium with the air.

• Seeds, and very select group of plants/animals are able to do this.

• In seeds, the proteins necessary for desiccation are already present

• In grown plants, the proteins are expressed when they’re needed

Resurrection Plant• Small number of plants can desiccate themselves virtually completely• In callus tissue, it only becomes desiccation-resistant when ABA is administered first.• In full plants, ABA level goes up as the plant is deprived of water. Several hundred

genes are expressed, mostly late embryogenesis abundant proteins.• When the plant is deprived of water, it produces ABA.• However, if a plant is mutated so that CDT-1 gene is constitutive, ABA is not required

for desiccation tolerance in callus tissue.• Several hundred genes are expressed. A large number of them are hydrophilic

proteins.• Hydrated leaves have high

Carbohydrate Metabolism

• Octulose is an intermediary sugar in photosynthesis. Resurrection plants horde it.

• As a plant dehydrates, it’s converted to sucrose, and then during rehydration, converted back to octulose.

• In C3 plants, octulose concentration goes up during day, and at night is converted to sucrose.

• It’s like that the same enzymes that are responsible for octulose conversion in all C3 plants are also used during dehydration/rehydration.

• Crowe finds that sucrose prevents protein denaturation.