Quiescence and Dormancy in Somatic Embryos

Abstract

Certain organisms avoid stress by entering a state of deep rest or dormancy; an adaptive mechanism that allows colonization of otherwise unfavorable environments. During dormancy, need for nutrients is greatly reduced as is sensitivity to environmental changes, thereby ensuring survival through hostile periods, such as dry or cold seasons. The adaptive range of organisms that possess this ability is greatly increased. For example, in the animal kingdom, a number of different taxa, notably phylum Tardigrada (tardigrades), can become dormant upon dehydration, which allows them to survive dry periods. Others, such as the fairy shrimp (Eubranchipus) produce eggs that withstand severe drying (Hickman et al. 1974). They become active and reproduce upon rehydration during moist periods. Such animals can, thus, survive and thrive in areas that are subjected to periodic cycles of drying and wetting. Plants such as Selaginelle lepidophylla (Hook, and Grev.) Spring behave similarly (Adams et al. 1990); they stop growth and shrivel during unfavorable dry seasons but resume a normal appearance and growth habit upon rehydration. Both of these diverse types of organisms can remain dormant and survive prolonged periods of dehydration.