PHASE CHANGE: PHYSIOLOGICAL AND GENETIC ASPECTS

Progression through the life cycle in many organisms involves the gradual acquisition of new combinations of morphological and physiological characteristics which differ only slightly from those of the preceding state.
In some organisms, however, development is characterized by the sudden replacement of one persistent state (juvenile) by another persistent state (adult) which differs greatly in morphology and physiology from the preceding state.
Such sudden developmental transitions are called phase changes.
Defined in this way phase change is a relatively common phenomenon in the development of plants and animals, and includes the transition from production of vegetative organs to production of floral organs by a shoot meristem, the transition from production of submerged leaf type to production of emergent leaf type in aquatic plants, the transitions between gametophyte and sporophyte in apogamous and aposporous ferns and the transition from larva to pupa to adult in holometabolous insects.

If progression through the normal life cycle is regulated by the selective activation of genes specific to each developmental stage, then the questions to be resolved in the case of phase change are the following: How is the large number of genes that must regulate the expression of a specific phase turned on or off coordinately? What are the molecular and cellular mechanisms that underlie coordinate gene activation? How does the organism measure developmental time so that phase transition occurs predictably?

Symposium on Juvenility in Woody Perennials

I. Sussex

https://doi.org/10.17660/ActaHortic.1976.56.32