Dehydrins in Orthodox and Recalcitrant Seeds

Dehydrins is a complex family of hydrophilic heat-stable proteins. Their properties and functions are inadequately studied. They are accumulated in plant tissues in response to any external stimulus causing dehydration of the cells. These stimuli may result from drought, salt stress, cooling, treatments with hormones, and seed maturation. Dehydrins are identified in cyanobacteria, tissues of gymnospermous and angiospermous plants, herbaceous and woody species, vegetative organs, and various embryonic tissues of seeds. They are thought to be essential elements in plants' resistance or tolerance to dehydration. Plant seeds are of special interest for investigating this group of proteins. In the resistant to dehydration orthodox seeds, dehydrins are synthesized and accumulated at the final stages of maturation associated with seed desiccation. Recalcitrant seeds that are sensitive to dehydration do not dry out upon maturation and retain high moisture content and active metabolism. These seeds are capable of dehydrin production but remain sensitive to water loss and cannot cope with a profound desiccation, unlike orthodox-type seeds. The review considers main properties and functions of dehydrins, their structure, classification, spread, and intracellular localization. Roles of dehydrins in recalcitrant seeds are discussed.