HISTOLOGY OF EMBRYOGENIC FORMATIONS DURING INVITRO CULTURE OF OIL PALM ELAEIS-GUINEENSIS JACQ

Histological analysis was carried out to investigate the formation and evolution of embryogenic cells and nodules during in vitro vegetative propagation of oil palm. Primary calli isolated from explants proliferated on a medium with 2,4-D, cytokinine and activated charcoal. When culture conditions were favorable the cambium-like zone which assumed the proliferation of nodular calli became embryogenic. This histological modification was described. Embryogenic cells became isolated specially towards the edges of the calli, undergoing few internal divisions but the proembryos formed did not develop further. The stoppage of this unicellular process was discussed. Evolution of the calli continued from the numerous meristematic centres which then formed. These centres were made of very active cells displaying special characteristics which were described. The activity of these centres resulted in the emergence of small whitish nodules. These became isolated with the formation of an epidermis, polarized and gave rise to somatic embryos. At this stage, they were transferred to a hormone-free medium where adventitious budding took place. This multicellular process in oil palm somatic embryogenesis is discussed in relation to histological work on other palms.