Understanding the Mechanism of Gamete Release in <i>Sargassum vulgare</i> C. Agardh

Abstract

Sargassum vulgare C. Agardh shows androgynous receptacles, each bearing on an average 12 unisexual conceptacles which open outside by ostiole, and wherein gametangia (antheridia or oogonia) lie interspersed with paraphyses. Since out-put of eggs is extremely low, 4 -6 per female conceptacle, Sargassum sp. ensures its survival under all ecophysiological conditions. The released oogonium is "wrapped" in sulphated polysaccharide-rich wall layer known to provide protection against desiccation. Oogonia after being "extruded" out of ostiole, are "incubated" on receptacle, where they grow into eggs that are easily contacted by spermatozoids. Gamete release is synchronous and almost simultaneous ensuring high rates of fertilization. The release occurs on days falling near a full moon or new moon, during low tides when conceptacles lie exposed. Gamete release occurs first from upper conceptacles, which "house" mature gametangia while lower ones are still developing. This results in gamete release over an extended period of time. The zygote dispersal and propagule recruitment also show adaptations selectively advantageous for the alga.

Environmental factors on egg liberation and germling production of Sargassum muticum

“…This could suggest that the eggs are irreparably damaged during this process, and those that are released simply fall off, following reimmersion. Alternatively, many of the released eggs may have actually survived the desiccation and are then extruded normally upon re-immersion, protected within the receptacle and layers of sulphated polysaccharides which are known to prevent desiccation (Kaur and Kumari 2012). The damage may instead occur within the male receptacle which produces less mucilage than the female receptacle (Kaur and Kumari 2012).…”

“…Alternatively, many of the released eggs may have actually survived the desiccation and are then extruded normally upon re-immersion, protected within the receptacle and layers of sulphated polysaccharides which are known to prevent desiccation (Kaur and Kumari 2012). The damage may instead occur within the male receptacle which produces less mucilage than the female receptacle (Kaur and Kumari 2012). This may allow damage to the antheridium preventing the release of viable spermatozoids, which are thought to be the most sensitive stage of their reproductive process (Hales and Fletcher 1990).…”

“…Male and female reproductive structures develop in separate conceptacles on the same receptacle. During reproduction, an egg is produced from each oogonium, which is exuded through the ostiole but remains bound to the adult by a mucilage sheath for several days (Fletcher 1980;Hales and Fletcher 1990;Kaur and Kumari 2012). This incubation period allows fertilization and initial germling development to occur whilst being attached to the adult.…”

Fucoidans of brown algae: Biosynthesis, localization, and physiological role in thallus

“…A similar distribution of fucoidans are observed in the cell wall of the filamentous brown alga Sphacelaria furcigera [31]. In the oogonia of fucoid algae, fucoidans are localized in the inner layer of cell wall adjoining the plasma membrane and in the vesicles of egg cells [58,76,103].…”

“…In generative structures, fucoidans are determined hystochemically as the main component of the extra cellular matrix (ECM) and mucilage "plugs" in the ostioles of conceptacles in fucoid algae [50,58,76,104,105]. The concentration of these polysaccharides in the ECM of conceptacles is several dozens of times higher than that in the ECM of medulla [104,105].…”