Embryology of zygote and development of germling in Sargassum vachellianum Greville (Fucales,Phaeophyta)

Sargassum vachellianum Greville is one of the most important members in the subtidal seaweed flora along the coasts of the Eastern China Sea. In order to understand the embryology of zygotes and development of germlings in S. vachellianum, we performed artificial ripening, systematically observed the morphological changes and development of the fertilized eggs and germlings, and explored the effects of culture conditions on the growth of the germlings. The receptacles matured, and eggs and sperm were released after 1–5 days of culture at 21–24 °C under 60–90 μmol photons m^?2 s^?1 (14L:10D). Once fertilized, zygotes immediately detached from the female receptacles and began to germinate. Eight nuclei in the released fresh zygote soon begun to fuse, forming a large central nucleus, and underwent two horizontal divisions to produce a small “original rhizoid cell,” which eventually formed rhizoids after several divisions, and three other cells which eventually formed landmine-like germlings after several continuous divisions. The germlings then formed rhizoids and attached onto the bottom of the flask within 12 h of culture. The growth and development of the germlings younger than 20 days were significantly influenced by the culture temperature and light, with the optimal conditions being 21 °C and 40 μmol photons m^?2 s^?1. However, for germlings older than 30 days, the optimal conditions were 24 °C and 60 μmol photons m^?2 s^?1.