Re-Formation and Ordering of Wall Microtubules in Spirogyra Cells

Abstract

Processes of re-formation and ordering of wall microtubules (wall MTs) in Spirogyra cells were examined using immunofluorescence microscopy. Wall MTs were usually arranged nearly transversely to the cell axis at all stages of the cell cycle. Two-hour treatment with amiprophosmethyl (APM) completely disrupted wall MTs, but removal of the APM led to re-formation of randomly oriented wall MTs at many sites over the cell. The re-formed wall MTs gradually assumed a transversely oriented order without any specific MT-ordering centers, indicating that initiation and ordering of MTs are different processes. Removal of APM after 24-h treatment caused reformation of randomly oriented wall MTs, followed in some cells by gradual ordering to obliquely oriented instead of transversely oriented wall MTs. This ordering occurred with the same sign of obliquity as that of chloroplast spirals. When cells were centrifuged along the cell axis, chloroplasts sedimented on the cross wall, but the transverse wall MTs did not. In centrifuged cells, wall MTs were re-formed and ordered transversely after MT depolymerization by APM for 2 h as in non-centrifuged cells. When cells were centrifuged for the final 30 min in 2-h treatment with APM, wall MTs that re-formed after removal of APM were sometimes ordered transversely over that part of the cell which contained sedimented chloroplasts, but remained at random over the other part, as though the MT-ordering factor was sedimented by the centrifugation. The mechanism determining the wall MT orientation is discussed.