Phase Change in Higher Plants and Somatic Cell Heredity

Publisher Website
Google Scholar
Abstract
Phase change sometimes involves a relatively abrupt switch in potential of apical meristems in higher plants from a juvenile to an adult type of growth. The two growth forms are highly persistent in different parts of the same individual and in clonally propagated offspring. Reversion to the juvenile condition occasionally occurs in buds on adult-type shoots, and invariably takes place in sexual reproduction. It is pointed out that counterparts of phase change, expressed in a wide variety of ways, are common among both plants and animals; structures arise in the development of all organisms with characteristics that are not merely functional adaptations but are innate and selfmaintaining in mitosis. Phase change is to be considered, therefore, as illustrating a general aspect of cell heredity and variation; it is singular only in the distinctness with which the alteration in type of growth may be phenotypically expressed. The mechanism whereby such characteristics are maintained and perpetuated in somatic cells is an unsolved problem. There is now limited evidence, some of it also indirect, suggesting that the chromosomes are the site of such discontinuous and potentially reversible ontogenetic changes. This evidence is briefly reviewed in terms of a hypothesis in which it is assumed that in addition to the genes, which are stable, the chromosomes also contain self-perpetuating accessory materials that undergo paramutation in an orderly way in somatic cells as an essential aspect of a nucleo-cytoplasmic system of morphogenetic determination.