Dep. Invertebrate Zoology, Biological Faculty, M.V.Lomonosov Moscow State University, Vorob'evy Gory, Moscow 119899, Russia

Abstract

Cell migration in ectoderm of stolons (and at less degree - in the shoots) during the growth of intact colonies of hydroid Gonothyraea loveni (Allm.) was studied by means of video-taping and vital staining. There are at least two main types of cell migration during colony growth: a) individual cell migration; b)entire tissue layer migration. The cells that migrate individually are nematoblasts (or nematocytes) and the morular cells with granulated cytoplasm. They move in the ectoderm layer along the basal membrane with speed up to 7-10 micrometers per minute in both direction - towards the growing tip and away from it. The individually migration cells can be found everywhere in the colony, but are more numerous in the younger parts. In stolons the tissue layer migration is observed in 2-3 distal internodes. Just behind the growing tip the tissue moves with the same speed as the growing tip. But at the base of the most distal shoot the speed of tissue layer migration on the side and base of the stolon tube can be two times higher than that of the growing tip. Within the last completely formed internode tissue layer migrates along its sides faster than movement of the tip, however it quickly comes down within the previous internode. On the upper surface of the stolon tube in the central part of the internode the speed of tissue layer migration insignificantly differs from those on its sides. But at the base of the shoots the speed of tissue layer decreases, and from vicinity of the shoot the tissue moves into its base. And the tissue on the sides of the stolon tube beside the migration towards the growing tip moves up on the upper surface of the tube. The same picture is observed in the shoots. Interesting is that during replacement of the dedifferentiated hydranth at any position within the shoot the cell material for it formation comes mostly from the lower parts of the shoot. The tissue layer migration is an active process and is not directly connected with the movement of the growing tip. On the other hand the tissue layer migration can play role in patterning processes due to the different speed of tissue layer migration on different sides of the coenosarc tube.