Morphological and photosynthetic variations in the process of spermatia formation from vegetative cells in Porphyra yezoensis Ueda (Bangiales, Rhodophyta) and their responses to desiccation.

Porphyra yezoensis has a macroscopic foliage gametophyte phase with only a single cell layer, and is ideally suited for the study of the sexual differentiation process, from the vegetative cell to the spermatia. Firstly, we compared variations in the responses of the vegetative and male sectors to desiccation. Later, cell tracking experiments were carried out during the formation of spermatia from vegetative cells. The two sectors showed similar tolerance to desiccation, and the formation of spermatia from vegetative cells was independent of the degree of desiccation. Both light and scanning electron microscopy (SEM) observations of the differentiation process showed that the formation of spermatia could be divided into six phases: the one-cell, two-cell, four-cell, eight-cell, pre-release and spermatia phases. Photomicrographs of Fluorescent Brightener staining showed that the released spermatia had no cell walls. Photosynthetic data showed that there was a significant rise in Y(II) in the four-cell phase, indicating an increase in photosynthetic efficiency of PSII during this phase. We propose that this photosynthetic rise may be substantial and provide the increased energy needed for the formation and release of spermatia in P. yezoensis.