Author
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Vaughn, Kevin |
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Bowling, Andrew |
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Submitted to: Protoplasma
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/13/2008 Publication Date: 7/30/2008 Citation: Vaughn, K.C., Bowling, A.J. 2008. Recovery of Microtubules on the Blepharoplast of Ceratopteris Spermatogenous Cells after Oryzalin Treatment. Protoplasma 233:231-240. Interpretive Summary: About one quarter of all herbicides interact direct with a cellular structure called a microtubule, but recognition of the sites where these microtubules are formed is still unknown. In this study, scientists in the Southern Weed Science Research Unit in Stoneville MS, studied the recovery of microtubules after recovery from the herbicide oryzalin in a special cell type in a fern plant where microtubules are formed from one structure. After herbicide treatment, this structure was studded with little holes that represent the nucleating site for the microtubule. After the herbicide was washed out the microtubules all grow from these sites and nowhere else. These data show that microtubules are formed at recognized sites, similar to those observed in mammalian cells. Technical Abstract: Most land plants have ill-defined microtubule-organizing centers (MTOC’s), consisting of sites on the nuclear envelope or even along microtubules. In contrast, spermatogenous cells of the pteridophyte Ceratopteris richardii have a well-defined MTOC, the blepharoplast, which organizes microtubules through the last two division cycles. This allows a rare opportunity to study the organization and workings of a structurally well-defined plant MTOC. In this study, antheridial plants were treated with levels of oryzalin that cause complete microtubule loss from the cells containing blepharoplasts and then washed out and allowed to recover for varying amounts of time. If the spermatogenous cells are fixed prior to any washing out the blepharoplasts have an unusual appearance. In the matrix (pericentriolar) material where MT ends are normally found, clear areas about the diameter of MT’s are seen embedded in a much deeper matrix, made more obvious in stereo pairs. Occasionally, the matrix material is highly distended although the basal body template cylinder morphology appears to be unaltered. Often the blepharoplasts occur as clusters of 2-4, indicating that blepharoplast reproduction is not affected by the lack of microtubules, but that their movement is. Gamma (') tubulin antibodies label the edge of the blepharoplast in areas where the pits are located, indicating that these might be sites for microtubule nucleation. After wash out, the new microtubules always re-occur on the blepharoplast and the recovery occurs within an hour of washout. Microtubule lengths increase with increasing time of the washout and after 24h of recovery are indistinguishable from untreated blepharoplasts. After washout, arrays in the sperm cells such as the spline and basal bodies were often malformed or present in multiple copies, as were the blepharoplasts in these cells prior to wash out. These data indicate that the blepharoplast serves as the site of microtubule nucleation and organization even after complete microtubule de-polymerization. Furthermore, the size of the pits on the microtubule-less blepharoplast and the reaction of these areas with tubulin antibodies indicate that these may represent the tubulin ring complexes of land plants, analogous to those known in mammalian systems. |
