Introduction to somatic embryogenesis
Biotechnology is considered as one of the most important dynamic tools in the development of sustainable agriculture. Somatic embryogenesis is defined as the development of structures that follow histodifferentiation patterns resembling the events observed in zygotic embryogenesis. This in vitro morphogenetic pattern is a multi-step regeneration process starting with the induction of pro-embryogenic masses, followed by somatic embryo formation, maturation, desiccation and plant regeneration, in response to physical and chemical treatments. Somatic embryogenesis is one of the techniques that emerged in recent years with the potential of providing an efficient clonal propagation system. Somatic embryogenesis can be a very efficient propagation method, if developed with high frequency selections. It has produced up to sixty thousand embryos from a gram of alfalfa leaf tissue. With such advantages, the production of artificial seeds is normally the next step. Furthermore, using this method, somaclonal variation in plants virtually disappears, hence ensuring genetic uniformity in the propagules. There are two different ways of induction of somatic embryogenesis: direct somatic embryogenesis (DSE) and indirect somatic embryogenesis (ISE).
Direct somatic embryogenesis (DSE) and indirect somatic embryogenesis (ISE)
DSE is when a minimal proliferation of unorganized tissue precedes embryo formation while in ISE callus proliferates profusely before embryo formation. It has been suggested that in DSE, proembryogenic competent cells are already present and the expression of the embryogenetic program merely depends on favorable conditions. We believe that a minimal reprogramming is required for DSE expression, whereas in ISE a major cell reprogramming is necessary for de-differentiation to acquire the embryogenic. The main factors involved in each case depend on the nature and...