Influence of inorganic and triethyl lead on nuclear migration and ultrastructure of Micrasterias

Abstract

Developing cells of three strains of the desmidiacean alga Micrasterias were treated with inorganic and triethyl lead and examined by light and electron microscopy. In the concentration range 12 to 30 μ M, triethyl lead disturbed normal development of the algae, caused changed dictyosomal ultrastructure, disturbed the formation of the secondary cell wall, and caused accumulation of lipid material. Cell multiplication was strongly inhibited between 5 and 30 μ M TriEL in Micrasterias denticulata, showing complete inhibition at 15 μ M and above. In addition, nuclear migration of developing Micrasterias cells was selectively disturbed by growth-inhibiting concentrations of TriEL, resulting in unusual positioning of the post-telophase nucleus. Although inorganic lead proved to be much more poisonous to Micrasterias cells than TriEL and caused bursting of the cells even at the low concentration of 3 μ M it did not affect nuclear migration. Electron microscopic observations revealed a complete disassembly of the post-telophase system of microtubules which is involved in nuclear migration by TriEL, but no detectable effect on the isthmus system of microtubules which anchors the nucleus in the isthmus. It is concluded that the disturbance of nuclear migration in Micrasterias by TriEL was due to the selective disassembly of the involved microtubule system.