Histological studies of cellular differentiation during somatic embryogenesis of coconut plumule-derived calli

Abstract

Since coconut is   one of the most recalcitrant species to generate in vitro, it is   necessary to study in detail about the cellular changes that occur during   somatic embryogenesis to enhance our knowledge about this phenomenon. In the   present study, coconut plumular tissues, the shoot meristem including leaf   primordia, were used as explants for in vitro regeneration studies.   Histological studies were carried out in different stages of plumule culture.   No noticeable growth was observed in 15 days old cultures. After 30 days,   meristematic cells could be identified. Abundance of meristematic cells,   foremost to the development of callus structures, was observed after 45 days.   After 75 days, globular friable calli were formed and histological studies   revealed the presence of meristematic centers which eventually formed somatic   embryos. The histological study of matured somatic embryos formed after 120   days of callus initiation showed a clear meristematic zone of parenchyma   cells, surrounded by vascular bundles. Histological studies, carried out for   certain abnormalities like compact calli, abnormal somatic embryoids with   rudimentary shoots and multiplied roots, revealed the presence of intact   cotyledonary leaves which seemed to inhibit the apical meristem development   of somatic embryoids. The presence of vascular bundles in the early stages of   callus formation might lead to the direct formation of meristemoids. These   results could aid future studies leading to enhanced control of the somatic   embryogenic process and greater efficiency of somatic embryo and plantlet   formation in coconut.