ABSTRACT
Isolated protoplasts have become most useful for studies in plant physiology, genetics and plant breeding. Three different pathways led to regeneration: moss cells formed protonemata from which gametophores were differentiated; in seed plants, either the formation of adventitious shoots was followed by rooting of cuttings or by grafting, or embryo-like structures were organized which then developed directly into plants. The term "regeneration" already applies to the formation of a cell by synthesis of a new cell wall. It is used here in the sense of reorganization of shoots and plants. Regeneration from protoplasts has been proposed as a useful method for clonal propagation as well as for detection and segregation of somaclonal variation of the donor material. Discrimination between initiation of plant regeneration on the one hand and resumption of regeneration which had already been initiated on the other hand turned out to be difficult in a number of cases.
