THE MITOTIC APPARATUS DURING UNEQUAL MICROSPORE DIVISION OBSERVED BY A CONFOCAL LASER-SCANNING MICROSCOPE

The structure of the mitotic apparatus during the microspore division of Tradescantia paludosa, which has a distinctively unequal division o f large vegetative and small generative cells, was studied using alpha -tubulin immunofluorescence methods and confocal laser scanning micros copy. Mitotic apparatuses began to develop asynchronously during early prophase at the vegetative pole (VP) and during prometaphase at the g enerative pole (GP). Both, however, reached completion together at the same time during metaphase. At the VP from prophase to prometaphase, microtubules (MTs) did not converge on the pole, and there was a circu lar area containing only a few MTs. The prophase spindles on the VP si de were in the form of domes or cones that lacked the top. In the meta phase, however, the MTs concentrated at the pole to form a representat ive cone-shaped half-spindle. At the GP from prometaphase to metaphase , the MTs did not concentrate, and a circular area existed that lacked MTs. The half-spindles formed truncated cones. When the phragmoplast developed and curved around the generative nucleus during the telophas e, it first grew toward the long axis of the ellipsoidal-shaped micros pore; and after it arrived al the inner membrane of the microspore, it again curved past the generative nucleus toward the short axis. In co nclusion, it was found that the mitotic apparatus of T. paludosa micro spores with its asynchronous growth and asymmetrical spindle structure and with its three dimensional growth of phragmoplasts had a peculiar developmental manner related to unequal division.