On the toxic effects of tetraethyl lead and its derivatives on the chrysophyte Poterioochromonas malhamensis. VI. Effects on lorica formation, mitosis, and cytokinesis.
Effects of tetraethyl lead (TEL) and derivatives triethyl lead (TriEL), diethyl lead (DiEL), and inorganic lead (Pb) on lorica formation of the unicellular alga Poterioochromonas malhamensis were investigated by light and electron microscopy. Lorica formation is microtubule (MT)--mediated and disturbed by agents interfering with MTs. TEL, largely ineffective as such, inhibited lorica formation of P. malhamensis when the lead compound was illuminated during or before the experiment. TriEL inhibited most; DiEL produced qualitatively effects similar to those of TriEL at about 10 times higher concentrations. Inorganic lead was even less toxic and did not selectively inhibit lorica formation of the algae. Low concentrations of TriEL (5 to 7.5 microM) selectively disturbed lorica formation, causing formation of numerous stalk-less loricae which exhibited gross and ultrastructural alterations like those induced by the antimitotic drug colchicine. The effects of TriEL on mitosis and cytokinesis of P. malhamensis were also investigated. The most sensitive mitotic phase was metaphase, which, however, accumulated only up to 5% after treatment of the cells with toxic concentrations (10 microM) of TriEL for 24 hr (control, 2%). On the other hand, up to 15% telophases (including binucleated cells) and even multinucleated cells with up to eight nuclei per cell were found, indicating that cytokinesis was considerably more effectively disturbed by TriEL than mitosis. In giant multinucleated algae, mitoses normally proceeded synchronously; some asynchronous mitoses were found. Beside normal-looking mitotic spindles in giant algae, multipolar spindles, disoriented spindles, and metaphase-like chromosome arrays completely lacking MTs were observed by electron microscopy. The effects of TriEL on cytokinesis of the algae were largely reversible. Giant cells spontaneously recovered and underwent cytokinesis after transferred into TriEL-free growth medium. Colchicine acted qualitatively identical to TriEL (accumulation of metaphases and telophases: 5 and 19%, respectively), but TriEL was about 600 times more toxic than colchicine. Unlike colchicine, its derivative, colchicine, which is known not to interfere with MTs, remained without any selective inhibitory influence on mitosis and cytokinesis of the algae, although much more toxic than the parent compound. From the inhibitory effects of TriEL and the close qualitative similarities to the effects of colchicine, it is concluded that TriEL selectively interferes with cytoplasmic and mitotic MTs of the algae, thereby causing the observed inhibitory effects on lorica formation, mitosis, and cytokinesis.
D002455:Cell Division / Q000187:drug effects*; D003078:Colchicine / Q000633:toxicity; D003903:Deuterium / Q000633:toxicity; D017666:Deuterium Oxide; D056890:Eukaryota / Q000187:drug effects / Q000254:growth & development / Q000648:ultrastructure; D008854:Microscopy, Electron; D008938:Mitosis / Q000187:drug effects*; D009942:Organometallic Compounds / Q000633:toxicity*; D013756:Tetraethyl Lead / Q000633:toxicity*; D014869:Water Intoxication
D009942:Organometallic Compounds; D013756:Tetraethyl Lead; D003903:Deuterium; D017666:Deuterium Oxide; D003078:Colchicine