The mechanism of adhesion and germination in the carpospores of Porphyra spiralis var. amplifolia (Rhodophyta, Bangiales)

Spore release is the primary means of dispersion employed by red algae, and it provides insight into the elements linking the stages of their life history. In most red algae, spores are released within a sheath-like envelope of mucilage, which is responsible for their primary attachment. However, few studies have characterized the polysaccharides involved in the adhesion of seaweed spores. Therefore, in this paper, the process of spore germination and adhesion in Porphyra spiralis var. amplifolia is described, as representative of the germination pattern of the Naccaria type. Using FITC-labeled lectins, we discovered high concentrations of α-d-mannose, α-d-glucose and β-d-galactose in the mucilage. The germ tube reacted with RCA-FITC, indicating the presence β-d-galactose, and the rhizoidal cells showed the presence of α-d-mannose, α-d-glucose and β-d-galactose, indicating their importance to substrate adhesion. Using light and transmission electron microscopy, we also conducted an analysis of spore ultrastructure. We found that the differentiation of a vacuole in the spore is one of the most important processes marking the initial stage of germination. Thus, as the degree of vacuolation increases, whole cell contents move towards the germ tube, which undergoes several successive divisions forming the sporophytic phase. Therefore, we can conclude that germination in Porphyra spiralis var. amplifolia is characterized by (1) the fixation of carpospores in the substrate by sugars present in the mucilage and (2) the polarization of cell contents by the processes of vacuolization and germ tube formation.

► The carpospores of Porphyra are released without a cell wall.
► The principal carbohydrate residues in the mucilage of Porphyra is β-d-galactose.
► The differentiation of a vacuole is one of important processes marking the carpospore.