Molecular Bases of Desiccation Tolerance in Plant Cells and Potential Applications in Food Dehydration

Abstract

Desiccation has many detrimental effects on the structure and function of biological membranes and proteins and this molecular damage decreases the freshness appearance of dehydrated foods. Phospholipid membranes are destabilised upon water stress by insertion of cellular amphiphiles, phase transition into the gel phase and membrane fusion. Proteins are denatured and electron transport chains are perturbed leading to increased formation of reactive oxygen species which cause irreversible damage of cellular structures. Cells respond to water stress by generating defense proteins and metabolites and eventually develop outstanding desiccation tolerance such as in the case of plant seeds and pollen, fungal spores, crustacean cysts, etc. The molecular bases for this remarkable phenomenon are not completely understood but several important principles have been identified. Three biological systems seem to act in concert to achieve desiccation tolerance: enzymes involved in osmolyte synthesis; proteins specialised in desiccation protection of membranes and proteins (LEA proteins), and antioxidant enzymes and molecules. Both osmolytes and LEA proteins contribute to stabilisation of membrane and protein structures by conferring preferential hydration at moderate desiccation and replacing water at extreme desiccation. Osmolytes also contribute to osmotic adjustment and act as hydroxyl radical scavengers. Genetically modified plants with increased production of these defenses could be useful to improve the quality of dried food.