Abstract
Features, development, and functions of preprophase bands (PPBs) of microtubules (MTs) are reviewed. The PPB is an array of cortical MTs in higher plants that appears in G 2 and prophase and predicts where the cell plate will be inserted (the division site). Experimental obliteration of the PPB causes misplacement of cell plate insertion, suggesting that the PPB is a determinant of the ultimate division site. Its development contains two elementary processes: Broad PPB formation first fixes the axis of division polarity in the cell, and PPB narrowing then defines the precise division site. The PPB disappears at the prophase/prometaphase transition stage, but it leaves information in some yet unidentified form at the division site. This information assists correct insertion of cell plates and maturation of new cell walls after cytokinesis. Several kinds of molecules are reported to occur in PPBs, but their roles are not yet understood. Actin and cyclin-dependent kinase homologs are suggested to be involved in the band narrowing MT, which is essential for PPBs to mature at the division site. Other possible functions of the PPB, such as premitotic nuclear positioning and prophase spindle orientation, are also reviewed.
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