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 mic rotubule (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 meri dional arrangement within 6 h after protoplast formation. At 6-9 h suc h MTs become highly concentrated and parallel to each other in certain areas. At 12 h the concentration is uniformly high throughout the cel l, indicating the completion of high density meridional arrangement of cortical MTs. Cortical MTs exhibiting a high density, meridional arra ngement show characteristics disassembly by treatment with 10 mu M ami prophos-methyl (APM) or cold treatment (0 degrees C). Disassembly occu rs by each MT unit at positions skipping 30-40 mu m in the transverse direction. and neighboring MTs subsequently disassemble to form MT gro ups. Each group becomes slender and then disappears completely within the following 24 h. The meridional arrangement of cortical MTs is disr upted 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 disruptio n and density return to normal levels following removal of NEM. It app ears that there are meridionally oriented channels, anchor-rich and an chor-poor, in the plasma membrane. The channels could be distributed a lternately and anchors could be deposited in a cross-linking manner wi th cortical MTs to form a stable cortical MT-cytoskeleton. MTs compris ing the cortical MT cytoskeleton could be oriented by meridionally ori ented channels of anchors which are distributed following establishmen t of cell polarity.