Participation of plant hormones in determination and progression of somatic embryogenesis

In vitro culture protocols have been developed for many species, mainly using empirical approaches, to induce somatic embryogenesis from various explant types. However, the underlying biochemical mechanisms governing induction, expression and maturation during somatic embryogenesis are still poorly understood. Among the signals that participate directly in the regulation of the different phases of this process, plant hormones emerged as candidates of choice. In this chapter, studies concerning the role of exogenously added plant growth regulators in somatic embryogenesis are reviewed. In addition, we discuss possible relationships between hormonal contents in starting explants and in cultures derived from them with their embryogenic competence. Moreover, information on evolution of endogenous plant hormone levels during induction and progression of somatic embryogenesis is presented. Finally, an overview of interactions between exogenous plant growth regulators and endogenous hormones in embryogenic systems is also included.