Development of oogonia of Sargassum horneri (Fucales, Heterokontophyta) and concomitant variations in PSII photosynthetic activities

Sargassum horneri is one of the most important seaweeds used to restore degraded coastal environments near Nanji Island, China. However, its reproductive characteristics, especially those of oogenesis and the concomitant changes in photosynthetic activities, remained uncertain. Herein we documented the processes of conceptacle and female gamete formation and the photosystem II (PSII) changes that accompanied them. Thalli of S. horneri were dioecious, the oogonial conceptacles maturing acropetally on the axillary receptacles. Conceptacles were originated from the epidermal cells, the cells lining the inner surface of the cavity ultimately differentiating into either sterile unbranched paraphyses or oogonia. The PSII photosynthetic activities of oogonia continuously diminished with increasing maturation. The value of Fv/Fm decreased from 0.55 ± 0.01 for recently initiated oogonia to 0.27 ± 0.05 for mature oogonia. The diameters of the oogonia increased approximately 20 times from initiation to maturity. The possible nutrition sources of oogonia during their development are discussed. © 2014 International Phycological Society.