ANTIBODY AGAINST PHOSPHORYLATED PROTEINS (MPM-2) RECOGNIZES MITOTIC MICROTUBULES IN ENDOSPERM CELLS OF HIGHER-PLANT HAEMANTHUS

In diverse cell types, monoclonal antibody MPM-2 recognizes a class of phosphorylated proteins related to microtubule organizing centers and abundant during mitosis. We have used this antibody in an attempt to identify the spatial and temporal localization of putative microtubule organizing centers in endosperm cells of the higher plant Haemanthus. Our results show that MPM-2 recognized epitope is present in interpha se cells and enriched in mitotic cells. In interphase the antibody usu ally stains cytoplasmic granules. During the interphase-prophase trans ition immunoreactive material appears in the nucleus, at the nuclear e nvelope, and in association with microtubules. Concomitantly, we obser ved an increase of immunoreactivity of the cytoplasm. During mitosis t he phosphorproteins recognized by MPM-2 are detected in the cytoplasm, in association with microtubules of the spindle, the phragmoplast, an d in the newly-formed cell plate. After completion of mitosis, only th e cell plate and cytoplasmic granules are MPM-2 positive. Extraction o f the cells with Triton X-100 prior to fixation removes staining of th e cytoplasm by MPM-2. The detergent resistant immunoreactive material remains associated with surrounding the nucleus microtubules of the pr ophase spindle, the core of kinetochore fibers, and the phragmoplast. In the phragmoplast, however, segments of microtubules which are dista l to the cell plate are depleted of MPM-2. These data demonstrate that microtubule arrays of endosperm cells are phosphorylated during mitos is. Thus, similar to animal cells, interphase and mitotic microtubules of higher plants have different properties. Additionally, the localiz ation of detergent resistant MPM-2 antigen points to the difference in microtubule nucleation/organization between higher plant and animal c ells. (C) 1995 Wiley-Liss, Inc.