Ultrastructural studies of gametogenesis in Laminaria angustata (Laminariales, Phaeophyta) regulated by iron concentration in the medium

Abstract

Gametogenesis is induced in female and male gametophytes of L. angustata Kjellman by transferring them to modified ASP-12 NTA medium containing 2 mg l⁻¹ Fe. Ultrastructural changes are described for each of the four successive stages of reproductive maturation. In vegetative gametophytes, the Golgi bodies pinch off characteristic small electron dense vesicles, and heterochromatin occurs at several sites in the nuclei. In early egg development, the Golgi bodies increase in number and actively produce large electron-transparent vesicles and nuclear chromatin disperses. In the mature oogonium, the endoplasmic reticulum becomes well-developed and expands slightly, and a large amount of osmiophilic material occurs. In the liberated egg, these osmiophilic inclusions decrease grapually. In early sperm development, Golgi bodies produce large vesicles but do not increase in number as in egg formation. After nuclear divisions, a sperm is formed in each antheridium and chromatin in the nucleus is generally condensed. Within an antheridium, flagellar basal bodies of a sperm are parallel, but these become arranged perpendicularly after a sperm is liberated. Near the basal bodies, two microtubule bands occur. One band consists of five microtubules and extends forward from the anterior flagellum; the other band consists of 3–4 microtubules. A cap-like structure, which occurs at the tip of wall of the oogonium and the antheridium and consists of granular material, is also described.