SEM and TEM characterization of embryogenic calli

--K. V. Rao, P. Suprasanna and G. M. Reddy

Within a week of culturing of immature embryos, embryogenic cells were formed as few sectors, after which the callus proliferated from the embryos. Numerous torpedo shaped embryoids could be seen on the embryogenic calli, under a dissecting microscope. At this stage, the embryogenic calli were separated and grown on MS medium supplemented with 2,4-D. The level of 2,4-D in the medium was crucial in maintaining the embryogenic competence of the calli. The embryogenic cells appeared small, and rich in cytoplasm, compared to non-embryogenic cells.

One-month-old subcultured embryogenic and non-embryogenic calli (originally separated from the primary calli that were initiated from the embryos), were characterized by scanning and transmission electron microscopy, to see the differences in cell types and organization between these calli. SEM studies revealed the presence of numerous globular structures besides exhibiting characteristic features of scutellum and coleoptile. The TEM studies revealed clear differences between embryogenic and non-embryogenic calli. Embryogenic cells were characterized by thin cell walls with uniformly distributed cytoplasmic material. On the other hand, the non-embryogenic calli showed thick cell walls with meagre cytoplasm along the cell wall.

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