John H. Crowe

Anhydrobiosis: the water replacement hypothesis

Both the association of amphiphiles to form phospholipid bilayers and the folding of proteins that results in their tertiary structure are profoundly influenced by the low solubility of hydrocarbons in water (e.g. Tanford, 1978). These molecular arrangements, which are thought to be entropically driven, are lost when the water in which they are formed is removed. For instance, when a biological membrane is dehydrated, irreversible changes occur in its structural (Crowe and Crowe, 1982) and functional (Crowe, Crowe and Jackson, 1983) integrity. Similarly, many labile proteins lose their functional (reviewed in Carpenter, 1994) and probably structural (Prestrelski, Arakawa and Carpenter, 1993) integrity when they are desiccated. However, since the mid-1970s evidence has been accumulating that certain sugars may replace the water around polar residues in membrane phospholipids and proteins, maintaining their integrity in the absence of water. In this review we provide a current summary of what is known about the mechanism of these effects.

Uptake of amino acids by juveniles of Carcinonemertes errans (nemertea)

Abstract 1. 1. Juveniles of the nemertean Carcinonemertes errans are capable of removing amino acids from dilute solution. 2. 2. Decay constants for removal of amino acids from solution ranged from 3.6 (glycine) to 0.43 (aspartate) μmol/g-hr. 3. 3. Seawater from areas on the crab Cancer magister inhabited by the worms contained concentrations of primary amines ranging from 36 to 180 μM glycine equivalents. 4. 4. Seawater from areas of the crabs formerly occupied by worms or from similar areas on crabs lightly infected with worms contained 650–715 μM glycine equivalents. 5. 5. The nemerteans were shown to be capable of removing these naturally occurring primary amines from solution.

Membrane Behaviour and Stress Tolerance in Pollen

Temperature and water stress are the most important of stresses imposed on pollen during maturation in the anther and after shedding. During dehydration, osmotic and salt stress become important, and enormous mechanical forces are exerted during the shrinking of the cell. Tolerance to desiccation, which is common among pollen species, requires the proper tactics of the cells towards both dehydration and rehydration. For long term survival in the dry condition a special biochemical composition may be required, which curtails free radical damage. Dry pollen usually ages slowly, particularly in the cold. In contrast, both high temperatures and elevated water contents considerably accelerate ageing. Because reduced vigour due to the above mentioned stresses usually coincides with increased solute leakage during imbibition, we focus on the conformational and compositional status of the membrane phospholipids.