Calcium-Sensitivity of Cortical Microtubules in the Green Alga Mougeotia

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Membrane ghosts were prepared from protoplasts of the green alga Mougeotia, and the Ca<2+>-sensitivity of microtubules on the ghosts was examined. Microtubules on the protoplast ghosts were not depolymerized by 3 min treatment with 1 mM Ca^<2+>. As the treatment was prolonged, some depolymerization of microtubules became evident, but even after 10 min about 50% of the ghosts showed no depolymerization. Ca<2+ >introduced into intact protoplasts seemed to be ineffective in depolymerizing microtubules; abundant microtubules were present on membrane ghosts prepared from protoplasts which had been treated with 2 × 10^<-5> M Ca^<2+> ionophore A23187 plus 1 mM Ca<2+> for 20 or 30 min. Neither 3 min treatment with 0.2% Triton X-100 nor with 1 mM Ca^<2+> solution containing 5 mM MgSO_4 and 100 mM KCl caused depolymerization of microtubules on protoplast ghosts. However, when given successively, these treatments caused complete depolymerization of microtubules. These results suggest that Mougeotia microtubules are stable to Ca^<2+> and that the stability is conferred by a microtubule-associated factor which can easily be removed by Triton X-100 treatment.
日本植物生理学会の論文