Plant regeneration from protoplasts: a literature review

Protoplasts can be isolated in large quantities from different plant tissues and organs. They have shown the ability to synthesize new cell walls and to regenerate complete plants when cultured in the appropriate media. Therefore, protoplasts are regarded as totipotent cells, which are well suited for fundamental studies on the one hand, and for genetic manipulation on the other. For crop improvement through genetic manipulation techniques, such as somatic hybridization, micro-injection and electroporation, plant regeneration from protoplasts is of essential significance. As early as 1892, Af Klercker succeeded in the mechanical isolation of relatively low numbers of protoplasts of Stratiotes aloïdes by sectioning plasmolysed tissue. The isolation of protoplasts of Lycopersicon esculentum, using cell wall degrading enzymes (Cocking 1960), was a great break-through in protoplast research. The enzymatic treatment enabled the routine isolation of relatively high numbers of protoplasts from almost every organ and tissue of a diversity of plant species. In the period between 1960 and 1970, due to the combined application of cytokinins and auxins, cultured protoplasts showed the ability to form cell walls and to undergo cell divisions leading to colony formation. In 1971, for the first time, plant regeneration from protoplasts was achieved in tobacco (Nagata & Takebe 1971; Takebe et al. 1971). Subsequently, regeneration has been described from protoplasts of a great diversity of plant species, especially those that belong to the Solanaceae.