Somatic embryo production in bioreactors

Abstract

Within the past ten years much progress has been made with various aspects of plant tissue culture and the outlook for in vitro genetic manipulation is considerably more encouraging. One of the more significant developments has been the demonstration of plant regeneration by somatic organogenesis and embryogenesis from various explants (Williams and Maheswaran, 1986; Tisserat et al., 1979; Sharp et al., 1980; Ammirato, 1989). Two different pathways for morphogenesis in vitro have been recognised, direct and indirect where plants can be obtained from the explant indirectly or directly via organogenesis or embryogenesis (Fig. 1). These pathways differ in the necessity of dedifferentiating the initial explant and differences in identifying the in vitro progeny when compared to the parent plant. Organogenesis is characterized by the production of a unipolar bud primordium with subsequent development of the primordium into a leafy vegetative shoot. The developing shoot induces procambial strands to establish a conducting connection between the young shoot and the maternal tissue. The shoot then becomes rooted via root primordia formation and subsequent root organogenesis. Organogenesis is considered as one of the most widely used commercial method of regeneration (Litz, 1986). The procedures are however, labour-intensive due to the number of manual manipulations involved and the low multiplication rates. Gradual acclimatization of plants to the greenhouse and then to the field is also needed. These numerous steps are accompanied by extensive costs and commercialization has been limited to high unit-value crops. The cost of tissue culture propagation using