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Figure 5.3 : Direct differentiation of somatic embryos from hypocotyl explants

 

The shoot-bud and embryo formation can be distinguished by the distinct morphological features. The shoot-bud is a monopolar structure. It develops from the procambial strands which establish a connection with the pre-existing vascular tissue dispersed within the callus or the cultured explants (Figure 5.4 A-D).

Figure 5.4: Shoot differentiation from callus tissue. A-B, Development of vascular nodules randomly in the callus, note a small shoot-bud originated from vascular tissue in figure B. C-D, Shoot-buds establish a connection with pre-existing vascular tissue developed from the callus

Plant regeneration from isolated cells, protoplasts or unorganized mass of cells (callus) is generally more difficult than that obtained from the intact explants such as, cotyledons, hypocotyl segments and immature embryos. The regeneration obtained through de novo differentiation of shoot buds or somatic embryogenesis directly from explants may also exhibit genetic variability.