AXENIC TISSUE CULTURE AND MORPHOGENESIS IN PORPHYRA YEZOENSIS (BANGIALES, RHODOPHYTA)

To better understand developmental phenomena in macroalgal tissue culture, we examined the morphogenesis of Porphyra yezoensis Ueda (strain TU-1) cultured aseptically in defined synthetic media . Generally, the filamentous thalli (sporophyte; conchocelis phase) of P. yezoensis were densely tufted with uniseriate filaments. The foliose thalli (gametophyte) were monolayered. In this study, axenic filamentous thalli retained their characteristic morphogenesis; there were no obvious differences between morphogenetic traits in unialgal and axenic conditions. However, conchospores, which might have developed into the foliose form under unialgal conditions, germinated into calluslike masses under axenic conditions. Most of the gametophytes gradually lost their typical morphogenesis after the first longitudinal cell division. Some of the calluslike masses developed rhizoidlike structures in several places or along the entire mass. Therefore, we concluded that P. yezoensis, in axenic cultures, loses its typical morphogenesis only during the gametophytic phase. The axenic tissue culture of Porphyra established in this study is a promising assay system for the identification of growth and morphogenetic factors.