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-I) cult ured aseptically in defined synthetic media. Generally, the filamentous tha lli (sporophyte; conchocelis phase) of P. yezoensis were densely tufted wit h uniseriate filaments. The foliose thalli (gametophyte) were monolayered. In this study, axenic filamentous thalli retained their characteristic morp hogenesis; there were no obvious differences between morphogenetic traits i n unialgal and axenic conditions. However, conchosphores, which might have developed into the foliose form undel unialgal conditions, germinated into calluslike masses under axenic conditions. Most of the gametophytes gradual ly lost their typical morphogenesis after the first longitudinal cell divis ion. Some of the calluslike masses developed rhizoidlike structures in seve ral places or along the entire mass. Therefore, we concluded that P. yezoen sis, in axenic cultures, loses its typical morphogenesis only during the ga metophytic phase. The axenic tissue culture of Porphyra established in this study is a promising assay system for the identification of growth and mor phogenetic factors.