By following anther culture procedure as stated in the foregoing section, calli were obtained from anthers of maize Dan-Sun 91. Before differentiation (three- to four-week old) some of the calli were fixed with 3% glutaraldehyde and postfixed with 1% buffered OsO4. Then they were further prepared for electron microscopy by embedding in Epon.
Under the electron microscope, it was observed that two types of cells were discernible: one was filled with cytoplasm and the other was occupied mostly by vacuole. The former were in general smaller than the latter. Both were irregular in shape.
The cells with full cytoplasm appeared to be actively growing. Their chloroplasts were well differentiated and starch grains were developed. However, grana thylakoids and stroma thylakoids were unclear. Mitochondria were also present and they were in general much smaller than chloroplasts. In most of the mitochondria, christae or inner membranes were well organized. In addition, these cells also had abundant endoplasmic reticulum with clearly defined ribosomes. The nuclei were located in the center of the cells or nearly so. On the other hand, those cells which had a large vacuole in the center appeared senescent. Their nuclei were apparently pushed to the periphery of the cells. Cytoplasms were dense and more darkly stained than those of the other group of cells described in the above. Organelles such as chloroplasts, mitochondria and endoplasmic reticulum were less developed. No starch grains were observed in the chloroplasts and no grana thylakoid and stroma thylakoid were present. Further studies on the ultrastructure of anther calli at various stages of development are in progress.
Margaret Yu
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