1. Introduction

Adventitious shoot proliferation in plant cell and tissue culture, in response to hormonal manipulation of the culture medium, require de novo differentiation of meristematic region, randomly, all over the tissue other than the pre-existing meristem. It is a multistep process and a series of intracellular events, collectively called induction that occurs before the appearance of morphologically recognizable organs. Micropropagation via adventitious shoot regeneration may occur directly or indirectly via an intervening callus phase (Figure 5.1A, B). Indirect regeneration often results in somaclonal variations, making this strategy less desirable for large-scale clonal multiplication (Marcotrigiano and Jagannathan 1988; Thorpe et al. 1991). Therefore, regeneration of shoots directly from the explants is regarded as the most reliable method for clonal propagation. Various explants like leaf, cotyledon, embryo and root have been tried with different media combinations by the scientists to obtain adventitious shoot proliferation.

Figure 5.1.: Organogenesis from leaf explants indirectly via callusing
A. Shoot differentiation B. Root differentiation

 

2.  Organogenic differentiation

Regeneration of plant from the cultured explant may occur either through differentiation of shoot-buds or somatic embryogenesis (Figure 5.2 A-E, and Figure 5.3).

Figure 5.2 : Direct shoot proliferation from leaf-disc culture