Dormancy and storage of geophytes

Dormancy is the temporary suspension of visible growth of meristematic structures. This phenomenon is widespread in the plant kingdom, and examples can be found in seeds, apical and lateral vegetative buds, floral buds, bulb, corms and tubers. Dormancy is an integral part of the annual life cycle of most geophytes, characterizing perennial plants that exhibit seasonal growth. In addition, evergreen geophytes of tropical origin are forced into a dormancy period in horticultural practice. Contrary to dormancy in tree buds and seeds, that of geophytes incorporates all types of dormancy: endodormancy, paradormancy and ecodormancy. The understanding of the mechanisms involved in the regulation of dormancy is very important since dormant geophytes are more resistant to environmental stresses, but only non-dormant planting material is expected to resume growth following planting. Studies of the hormonal regulation of dormancy are abundant. Clear roles for abscisic acid, as a dormancy inducing/maintaining hormone, and for gibberellins as dormancy breaking hormones have been revealed. Several reports support a similar role for ethylene. Although dormancy breaking involves modifications in overall cellular metabolism, no clear association between hormonal action and activated metabolism of geophylic organs has been described so far. Also, the molecular regulation of geophyte dormancy is very poorly understood. Results from our work with liatris and caladium tubers will be presented and discussed.