THE CYCLIC REORIENTATION OF CORTICAL MICROTUBULES IN EPIDERMAL-CELLS OF AZUKI-BEAN EPICOTYLS - THE ROLE OF ACTIN-FILAMENTS IN THE PROGRESSION OF THE CYCLE

The orientation of microtubules (MTs) was examined in epidermal cells of azuki bean (Vigna angular is Ohwi et Ohashi) epicotyls. The orienta tion of MTs adjacent to the outer tangential wall of the cells, which has a crossed polylamellate structure with lamellae of longitudinal ce llulose microfibrils alternating with lamellae of transverse cellulose microfibrils, differed from one cell to another. Treatment with an au xin-free solution caused the accumulation of cells with longitudinal M Ts and subsequent treatment with a solution that contained auxin resul ted in the accumulation of cells with transverse MTs, showing that seq uential treatments with auxin-free and auxin-containing solutions can synchronize the reorientation of MTs. The MTs, once reoriented from lo ngitudinal to transverse, returned to longitudinal and then back to tr ansverse once again, the duration of the cycle being about 6 h. Gibber ellic acid, known to increase the percentage of cells with transverse MTs, promoted reorientation of MTs from longitudinal to transverse and inhibited that from transverse to longitudinal. Cytochalasin D, an ag ent that disrupts actin filaments, speeded up the reorientation from t ransverse to longitudinal and slowed down that from longitudinal to tr ansverse. It caused an increase in the percentage of cells with MTs in mixed orientation, and the percentage of such cells was highest when the percentage of cells with longitudinal MTs was decreasing and that of cells with transverse MTs was increasing.