LIFTING THE CURTAIN - THE MICROTUBULAR CYTOSKELETON OF OXYRRHIS MARINA (DINOPHYCEAE) AND ITS REARRANGEMENT DURING PHAGOCYTOSIS

The cortical microtubular cytoskeleton of the colorless, phagotrophic dinoflagellate Oxyrrhis marina has been investigated by immunofluoresc ence and transmission electron microscopy. It consists of two systems, an anterior system comprising microtubular bands (of 2-4 microtubules each) which extend from a focal point at the cell apex to about three -quarters of the cell length where they either become transversely ori ented (on the ventral right surface of the cell) or abut transversely oriented microtubules (on the dorsal and ventral left cell surface); a nd a posterior system in which microtubular bands extend from a focal point near the basal apparatus posteriorly around the antapex of the c ell to become transversely oriented in the region where they meet the abutting anterior microtubular bands. The peripheral cytoskeleton of O xyrrhis contains no continuous pole-to-pole microtubules and is thus b asically similar to that of other dinoflagellates. Upon phagotrophic f eeding the peripheral microtubular cytoskeleton undergoes reversible r earrangements. The non-permanent cytostome is located at the right ven tral surface of the cell between the ventral ridge microtubules (vrm) and the groove of the longitudinal flagellum. During phagocytosis the anteriorly focused microtubular bands of the peripheral cytoskeleton n ear the right ventral surface of the cell are 'lifted' or 'pushed' tow ards the vrm to enable uptake of food organisms of diverse size and sh ape. Within minutes after phagocytosis the microtubular bands are relo cated to their former position. We conclude that the organization of a peripheral microtubular cytoskeleton from two opposite focal points p rovided the dinoflagellates with the flexibility needed to evolve the multitude of phagocytotic mechanisms that characterize this group of p rotists today.