Summary
Tissue of one-year-old leaves ofWelwitschia mirabilis was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. Mature sieve cells contain nuclei composed of peripherally-distributed chromatin material and an intact envelope with pores. During sieve-cell development many mitochondria become closely associated spatially with the nucleus. In addition to a nucleus and mitochondria, the mature, plasmalemma-lined sieve cell contains plastids and abundant smooth endoplasmic reticulum, which generally occurs in massive aggregates at the sieve areas. Dictyosomes and ribosomes are lacking and a tonoplast is not discernible in mature sieve cells. P-protein is not present at any stage of development.
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This work was supported in part by a grant from the South African Council for Scientific and Industrial Research and in part by the U.S. National Science Foundation (GB 31417).
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Evert, R.F., Bornman, C.H., Butler, V. et al. Structure and development of the sieve-cell protoplast in leaf veins ofWelwitschia . Protoplasma 76, 1–21 (1973). https://doi.org/10.1007/BF01279669
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DOI: https://doi.org/10.1007/BF01279669