SEM Study on Early Stages of Oil Palm (Elaeis guineensis Jacq.) Somatic Embryos

Oil palm (Elaeis guineensis Jacq.) is a plant with highest productivity of oil among others oil-producing plants with total product per year is 5-6 ton/ha. Micropropagation of oil palm by somatic embryogenesis has several advantages: homogenous plants, higher production of fresh fruit bunches and larger amount of high quality seeds in a relatively shorter time. Oil palm 635 clone (15 years old) from Marihat Research Station, North Sumatra was used in this research. Embryogenic cell suspension was established by inoculating friable callus into suspension initiation medium (SIM) supplemented with 100 ppm 2,4-D and 1 ppm BAP. After four weeks of culture in SIM, the single embryogenic cells differentiated into proembryos and globular somatic embryos. Thereafter, the embryos were fixed and observed by Scanning Electron Microscopy (SEM) to reveal surface structure and morphology of the embryos. Initially, the proembryos cell has smooth surface, then deposition of fibrilar material occurred on the old cell wall surface, which become excessive during its development. The deposition of fibrillar material covered the cell wall surface and new cell wall was established. The rapid growth of proembryos caused degradation of cell wall and triggered the cell wall turnover. Proembryos stage was indicated by the appearance of extracellular matrix called supraembryonic structure (snt). Oil palm embryo underwent first tissue differentiation at globular stage, which was observed through a protoderm covering the cell walls. Deposition of cuticular layer component also occurred at this stage. This component similar to cuticular wax crystal found in Arabidopsis. The globular embryo of oil palm also had a suspensor structure with snt structure on it. This phenomena indicated that the suspensor growth was inhibited on a proembryo-like stage