role of microtubules and cell-wall deposition in elongation of regenerating protoplasts of Mougeotia

Protoplasts of the filamentous green alga Mougeotia sp. are spherical when isolated and revert to their normal cylindrical cell shape during regeneration of a cell wall. Sections of protoplasts show that cortical microtubules are present at all times but examination of osmotically ruptured protoplasts by negative staining shows that the microtubules are initially free and become progressively cross-bridged to the plasma membrane during the first 3 h of protoplast culture. Cell-wall microfibrils are observed within 60 min when protoplasts are returned to growth medium; deposition of microfibrils that is predominantly transverse to the future axis of elongation is detectable after about 6 h of culture. When regenerating protoplasts are treated with either colchicine or isopropyl-N-phenyl carbamate, drugs which interfere with microtubule polymerization, they remain spherical and develop cell walls in which the microfibrils are randomly oriented.