Embryogenesis

Once a callus has formed, its component cells can go on to differentiate a second time, this time organising themselves into embryo-like structures called somatic embryos, or embryoids (Figure 5.5). Unlike a normal zygotic embryo, an embryoid arises without any fusion of male and female gametes - it develops directly from the somatic (non-reproductive) cells of the callus. Once formed, embryoids are not left to develop on the same medium; they are sub-cultured, i.e. transferred onto fresh medium, where they go on to develop into independent plantlets. This callus-to-embryoid-to-plantlet sequence is one of the two general regeneration routes covered in more detail as somatic embryo …