A few maize anther calli about four weeks old and less than three millimeters in diameter were isolated and fixed in 3% glutaraldehyde for two hours and rinsed and again fixed in 2% osmium tetroxide for one hour. The fixed calli were embedded in Epoxy resin and sectioned with MT-I ultramicrotome. Thin sections were doublestained with uranium and lead. All observations were made with EM Philips 200. The following characteristics of the calli were consistently found:
The nuclei were irregular in shape and varied a great deal in size. Chromatin was condensed and much darkly stained. With a limited amount of material studied, no dividing cells were identified. Hence fine structures of chromosomes were not available for study.
In the nucleoli, fibrous elements, frequently spirally arranged, were apparent. These elements were embedded in a homogeneous granular background which was also heavily stained. No vacuoles were present in the nucleoli.
In the cytoplasm well developed chloroplasts were not observed, but some proplastids. Thylakoids of the proplastids were limited in number, and generally only one or two were found in a single organelle. They were usually appressed to the inner membrane of the proplastids, and left the center devoid of any visible thylakoids. The number and size of proplastids were inconsistent from cell to cell. Mitochondria were abnormal and frequently extended into rod-shape. Some of them were clearly grown out into two or three branches. Cristae or membranes within the mitochondria were plentiful. Occasionally small lipid granules were observed in the matrix. Furthermore endoplasmic reticulum did not have the well-packed membranes. Instead the membranes were dilated and scattered in the cytoplasm. Only a few ribosome granules were attached to the surface of each membrane and most of the other ribosomes were in the hyaloplasm. Elements of microtubules close to the cell periphery were readily identifiable, and most of them were less than 2000 Å in length.
Y. C. Ting and R. McLellan
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