STRUCTURE AND ASSEMBLY OF THE CORTICAL MICROTUBULE CYTOSKELETON IN THE GREEN-ALGA, BOODLEA-COACTA

Examination was made of the structure and assembly of the cortical microtubule (MT) cytoskeleton in the coenocytic green alga Boodlea coacta (Dickie) Murray et De Toni by immunofluorescence microscopy. Cortical MTs in Boodlea protoplasts are arranged randomly bur some show a meridional arrangement within 6 h after protoplast formation. At 6-9 h such MTs become highly concentrated and parallel to each other in certain areas. At 12 h the concentration is uniformly high throughout the cell, indicating the completion of high density meridional arrangement of cortical MTs. Cortical MTs exhibiting a high density, meridional arrangement show characteristics disassembly by treatment with 10 mu M amiprophos-methyl (APM) or cold treatment (0 degrees C). Disassembly occurs by each MT unit at positions skipping 30-40 mu m in the transverse direction. and neighboring MTs subsequently disassemble to form MT groups. Each group becomes slender and then disappears completely within the following 24 h. The meridional arrangement of cortical MTs is disrupted by N-ethylmaleimide (NEM) accompanied by a remarkable reduction in density. The remaining MTs form groups at 30-40 mu m intervals from each other, as also occurs with drug or cold treatment, but disruption and density return to normal levels following removal of NEM. It appears that there are meridionally oriented channels, anchor-rich and anchor-poor, in the plasma membrane. The channels could be distributed alternately and anchors could be deposited in a cross-linking manner with cortical MTs to form a stable cortical MT-cytoskeleton. MTs comprising the cortical MT cytoskeleton could be oriented by meridionally oriented channels of anchors which are distributed following establishment of cell polarity.