Plants and animals that can survive
dehydration accumulate high concentrations of
disaccharides in their cells and tissues during desiccation. These
sugars are necessary both for the depression of the membrane phase transition temperature of the dry
lipid and for the formation of a
carbohydrate glass. In the past decade, however, it has become clear that certain types of adventitious enzymatic reactions are possible at low water contents, which along with
free-radical mediated damage, can cause hydrolysis of
lipids and loss of membrane barrier function.
Disaccharides do not necessarily prevent these types of reactions, which suggests that other compounds might also be necessary for protecting organisms from this type of degradation during anhydrobiosis.
Arbutin, one possible example, accumulates in large quantities in certain resurrection plants and has been shown to inhibit
phospholipase A(2) activity at low water contents. The direct effect of
arbutin on membranes under stress conditions depends on the
membrane lipid composition. It can serve a protective function during desiccation- or freeze/thaw-induced stress in the presence of nonbilayer-forming
lipids or a disruptive function in their absence. Other possible amphiphiles, including certain naturally occurring
flavonols, may serve as
anti-oxidants and some might have similar
lipid composition-dependent effects. Such compounds, therefore, are likely to be localized near specific membranes, where they might provide the greatest benefit at the least liability to the organism.