title: ASYMMETRY OF EYESPOT AND MATING STRUCTURE POSITIONS IN ULVA COMPRESSA (ULVALES, CHLOROPHYTA) REVEALED BY A NEW FIELD EMISSION SCANNING ELECTRON MICROSCOPY METHOD(1).
abstract: Gametes of the marine green alga Ulva compressa L. are biflagellate and pear shaped, with one eyespot at the posterior end of the cell. The species is at an early evolutionary stage between isogamy and anisogamy. In the past, zygote formation of green algae was categorized solely by the relative sizes of gametes produced by two mating types (+ and -). Recently, however, locations of cell fusion sites and/or mating structures of gametes have been observed to differ between mating types in several green algae (asymmetry of cell fusion site and/or mating structure positions). To use this asymmetry for determining gamete mating type, we explored a new method, field emission scanning electron microscopy (FE-SEM), for visualizing the mating structure of U. compressa. When gametes were subjected to drying stress in the process of a conventional critical-point-drying method, a round structure was observed on the cell surfaces. In the mating type MGEC-1 (mt(+) ), this structure was located on the same side of the cell as the eyespot, whereas it was on the side opposite the eyespot in the mating type MGEC-2 (mt(-) ). The gametes fuse at the round structures. TEM showed an alignment of vesicles inside the cytoplasm directly below the round structures, which are indeed the mating structures. Serial sectioning and three-dimensional construction of TEM micrographs confirmed the association of the mating structure with flagellar roots. The mating structure was associated with 1d root in the MGEC-1 gamete but with 2d root in the MGEC-2 gamete.
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Mogi
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Kagami
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Kuwano
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Miyamura
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Nagumo
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, JapanDepartment of Marine Science and Technology, Graduate School of Science and Technology, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, JapanThe Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, JapanDepartment of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Kawano
keywords: Ulva compressa; cell fusion; field emission scanning electron microscopy; flagellar roots; gamete; mating structure; sex