ULTRASTRUCTURF OF FERTILIZATION IN <i>LAMINARIA ANGUSTATA</i> (PHAEOPHYTA, LAMINARIALES) WITH EMPHASIS ON THE BEHAVIOR OF CENTRIOLES, MITOCHONDRIA AND CHLOROPLASTS OF THE SPERM<sup>1</sup>

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<jats:title>ABSTRACT</jats:title><jats:p>Fertilization and zygote development in <jats:italic>Laminaria angustata</jats:italic> Kjellman were observed ultrastructurally. Cell wall formation of the zygote is initiated immediately after plasmogamy. The zygote begins to elongate, chloroplasts move from the renter to the periphery, and the sperm nucleus moves toward the egg nucleus. Karyogamy occurs with both euchromatin‐rich female nucleus and hetero‐chromatin‐rich male nucleus in interphase. Cytoplasmic inheritance of centrioles, mitochondria and chloroplasts was examined, especially during zygote development of <jats:italic>L. angustata.</jats:italic> Two pairs of centrioles originating from the egg and sperm exist in the early zygote. Later, egg centrioles disappear and only sperm centrioles remain resulting in one pair of centrioles in the zygote. When mitosis of the zygote is initiated, the centrioles of the pair separate and are duplicated as they migrate to the poles, in a manner similar to that in brown algal mitosis. Sperm mitochondria are enclosed with endoplasmic reticulum (ER) and Golgi vesicles. The vesicles finally become single‐membrane vesicles, and enclosed mitochondria are digested. Small sperm chloroplasts do not fuse with egg chloroplasts, increase in size, or divide and can be detected even at the stage of two‐celled sporophytes. Therefore, almost all chloroplasts of the zygote and sporophyte originate from the egg.</jats:p>

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