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 T m

Rehydration T m –leaky membrane Disaccharides help! – –T m ?

Sucrose and Trehalose [solute] increases osmotic pressure Crowe believes Water replacement theory Vitrification

Ice Stabilize High viscosity T m Reverses with the addition of water T g solid  viscous

What am I?

ActiveDehydrated at high humidity

Low humidityAnesthetized

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.