Abstract
An ontogenetic study of the sieve element protoplast of Nicotiana tabacum L. by light and electron microscopy has shown that the P-protein component (slime) arises as small groups of tubules in the cytoplasm. These subsequently enlarge to form comparatively large compact masses of 231 ± 2.5 (SE)A (n = 121) tubules, the P-protein bodies. During subsequent differentiation of the sieve element, the P-protein body disaggregates and the tubules become dispersed throughout the cell. This disaggregation occurs at about the same stage of differentiation of the sieve elements as the breakdown of the tonoplast and nucleus. Later, the tubules of P-protein are reorganized into smaller striated 149 ± 4.5 (SE)A (n = 43) fibrils which are characteristic of the mature sieve elements. The tubular P-protein component has been designated P1-protein and the striated fibrillar component P2-protein. In fixed material, the sieve-plate pores of mature sieve elements are filled with proteinaceous material which frays out into the cytoplasm as striated fibrils of P2-protein. Our observations are compatible with the view that the contents of contiguous mature sieve elements, including the P-protein, are continuous through the sieve-plate pores and that fixing solutions denature the proteins in the pores. They are converted into the electron-opaque material filling the pores.
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Selected References
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- Esau K., Cronshaw J., Hoefert L. L. Relation of beet yellows virus to the phloem and to movement in the sieve tube. J Cell Biol. 1967 Jan;32(1):71–87. doi: 10.1083/jcb.32.1.71. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gall J. G. Microtubule fine structure. J Cell Biol. 1966 Dec;31(3):639–643. doi: 10.1083/jcb.31.3.639. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kallman F., Wessells N. K. Periodic repeat units of epithelial cell tonofilaments. J Cell Biol. 1967 Jan;32(1):227–231. doi: 10.1083/jcb.32.1.227. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ledbetter M. C., Porter K. R. Morphology of Microtubules of Plant Cell. Science. 1964 May 15;144(3620):872–874. doi: 10.1126/science.144.3620.872. [DOI] [PubMed] [Google Scholar]
- MILLONIG G. A modified procedure for lead staining of thin sections. J Biophys Biochem Cytol. 1961 Dec;11:736–739. doi: 10.1083/jcb.11.3.736. [DOI] [PMC free article] [PubMed] [Google Scholar]
- O'Brien T. P., Thimann K. V. Intracellular fibers in oat coleoptile cells and their possible significance in cytoplasmic streaming. Proc Natl Acad Sci U S A. 1966 Sep;56(3):888–894. doi: 10.1073/pnas.56.3.888. [DOI] [PMC free article] [PubMed] [Google Scholar]
- PEASE D. C. THE ULTRASTRUCTURE OF FLAGELLAR FIBRILS. J Cell Biol. 1963 Aug;18:313–326. doi: 10.1083/jcb.18.2.313. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Peters A., Vaughn J. E. Microtubules and filaments in the axons and astrocytes of early postnatal rat optic nerves. J Cell Biol. 1967 Jan;32(1):113–119. doi: 10.1083/jcb.32.1.113. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Phillips D. M. Substructure of flagellar tubules. J Cell Biol. 1966 Dec;31(3):635–638. doi: 10.1083/jcb.31.3.635. [DOI] [PMC free article] [PubMed] [Google Scholar]
- SLAUTTERBACK D. B. CYTOPLASMIC MICROTUBULES. I. HYDRA. J Cell Biol. 1963 Aug;18:367–388. doi: 10.1083/jcb.18.2.367. [DOI] [PMC free article] [PubMed] [Google Scholar]