Short Communication The Orientation and Localization of Cortical Microtubules in Differentiating Conifer Tracheids during Cell Expansion

Arrays of cortical microtubules (MTs) on radial walls in differentiating tracheids of Taxus cuspidata were ran-domly oriented when primary walls formed. The orienta-tion of MTs changed progressively from longitudinal to transverse as cells expanded. During formation of primary walls, MTs in differentiating tracheids disappeared locally at sites of future intertracheal bordered pits. In further differentiated tracheids, circular bands of MTs were ob-served around the edges of developing bordered pits. Key words: Bordered pit — Confocal laser scanning micros-copy — Cortical microtubule — Primary wall — Taxus cuspidata. The orientation of cellulose microfibrils (MFs) in the cell wall is of major importance in the determination of the direction of cell expansion and, thus, in the morphogenesis of plant cells (Green 1980, Seagull 1991). Cortical microtu-bules (MTs) are generally found lying parallel to newly deposited MFs in a wide variety of plant cells. In addi-tion, MT-depolymerizing agents, such as colchicine, usual-ly disrupt the orientation of MFs. These observations sup-port the hypothesis, originally proposed by Ledbetter and Porter (1963), that MTs control the orientation of newl