Cell wall structure of the agarophytes Gracilaria tikvahiae and G-cornea (Rhodophyta) and penetration by the epiphyte Ulva lactuca (Chlorophyta)

Use of light, transmission, and scanning electron microscopes revealed that the epidermal cell wall of the red algal agarophytes Gracilaria tikvahiae McLachlan and G. cornea J. Agardh consists of a decklamelle and outer and inner wall layers. The two species differed, with G. cornea having a significantly thicker outer wall and a more diffuse decklamelle. After induction, the zooids of Ulva lactuca would attach to glass slides and the two species of Gracilaria via an adhesion pad. Within a few days, 3-5 celled germlings penetrated the decklamelle and outer wall layer of both basiphytes. By the time the epiphyte germlings reached the 15 celled stage, they had penetrated the inner wall layer. The differences in epidermal cell wall construction between the two basiphytes may play a role in the ability of zooids of U. lactuca to attach in nature where epiphytization of G. cornea is infrequent.