COORDINATIVE NUCLEAR AND CHLOROPLAST DIVISION IN UNILOCULAR SPORANGIAOF LAMINARIA-ANGUSTATA (LAMINARIALES, PHAEOPHYCEAE)

Changes in the number of nuclei and chloroplasts were examined during the process of unispore formation in unilocular sporangia of Laminaria angustata. Just before meiosis, eight chloroplasts were always presen t in unilocular sporangial mother cells. The number of chloroplasts re mained constant through meiosis. After the resulting four nuclei divid ed again (third nuclear division), a close association between a nucle us and a chloroplast developed among each of the eight nuclei and eigh t chloroplasts. The eight chloroplasts divided almost synchronously be fore the synchronous division of the eight nuclei. Following the 16 nu cleate stage with 16 chloroplasts and the final 32 nucleate stage with 32 chloroplasts, 32 unispores, each with a nucleus and a chloroplast, were formed in unilocular sporangia of L. augustata. Immunofluorescen ce microscopy using an anti-cent-in antibody showed that two anti-cent rin-stained structures (as future mitotic poles) occurred adjacent to each of the premitotic four nuclei, and each spot was located near a c hloroplast. Therefore, after the third division, each of the eight nuc lei established close contact with a chloroplast presumably mediated b y the centrosomes.