2022 Volume 87 Issue 1 Pages 17-22
Multicellular marine algae have a simple body structure composed of just a small number of basic cell types. However, the mechanism of their cellular differentiation and multicellular morphogenesis remains mostly unknown. The multicellular leafy seaweed Gayralia oxysperma is composed of blade cells and rhizoid cells. In axenic culture, this species loses its typical multicellular morphology because, upon shaking, the two cell types separate to form a loose mass composed of the two cell types. This fragile cell mass was used to isolate each cell type for culture experiments and examination of their growth properties. Artificially synthesized thallusin, a morphogenesis-promoting factor, was also tested for its effect on the cells. The isolated blade cells are divided to generate daughter cells displaying various differentiation patterns, whether in the presence or absence of thallusin. None of the tested rhizoid cells divided but they elongated greatly to over 1 mm in length during 10 d of culture. These observations indicate that blade cells maintain their totipotency, while the rhizoid cells lose their abilities to divide and differentiate into other cell types. This result is in contrast to findings with the previously well-studied Ulva, which shares similarities with Gayralia in leafy morphology and early development but its rhizoid and stem cells retain their totipotency, while its blade cells do not. Therefore, the morphogenesis system in Gayralia seems to be fundamentally different from that of Ulva and requires further investigation.