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