INVESTIGADORES
LEONARDI Patricia Ines
congresos y reuniones científicas
Título:
Study of dwarf males of the freshwater alga Oedogonium macrandrium (Oedogoniales, Chlorophyta) with light and transmission electron microscopes.
Autor/es:
PATRICIA LEONARDI; SILVANA D'AMICO; EDUARDO CACERES
Lugar:
Río de Janeiro, Brasil
Reunión:
Congreso; 17 International Microscopy Congress; 2010
Institución organizadora:
Sociedade Brasileira de Microscopia e Microanálise
Resumen:
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Oedogonium macrandrium Wittrok is a dioecious freshwater green alga that presents sexual
dimorphism. The
complete development of the epiphytic dwarf males, from androspore germination to
the liberation of the mature male gametes, was studied. The task was carried out with both light and transmission electron microscopes.
Similar studies have been performed in multicellular dwarf males of Bulbochaete
hiloensis (Nordstedt) Tiffanyand pseudo-unicellular dwarf males of O. pluviale Nordstedt.
The material came from a pond located in the Parque de Mayo, Bahía
Blanca, Argentina. For light microscopy observations, the thalli were fixed
with glacial acetic acid/alcohol absolute (1:3) for 24 hours at room
temperature. The samples were stained with the following dyes: a) a solution of
45% propionic acid, 2% iron hematoxylin and 1% iron citrate b) aceto-iron hematoxylin/chloral
hydrate. For observations with transmission electron microscopy, the samples
were fixed with 1% glutaraldehyde and postfixed with 1% osmium tetroxide. Then,
they were dehydrated with acetone and embedded in Spurr resin. The
sections were contrasted with uranyl acetate and lead citrate.
Light
microscopy. The newly settled
androspore formed a finger-like holdfast and had a nucleus located in a
half-lateral position. Then, the germling developed
an apical division ring to whose level the nucleus migrated. Immediately afterwards,
the nucleus underwent a markedly asymmetric vegetative mitosis, and then 1) a
transverse septum was developed and 2) the division ring was expanded. As a
result, the dwarf male became composed of two uninucleate cells: a basal cell
and an antheridium. Successive similar mitosis and cytokinesis conducted
to the development of 2 (3) new antheridia. Each antheridial nucleus suffered then
a gametic mitosis and two gametes per antheridium were differentiated. The antheridia
maturation was basipetal, so that the first mature gametes were located at the
most apical antheridium, which were released through the opening of an
operculum.
Transmission
electron microscopy. The dwarf males initial nucleus exhibited a large
nucleolus. The cytoplasm showed large vacuoles,
abundant rough endoplasmic reticulum, especially in the holdfast, and
dictyosomes. There was also a reticulate chloroplast with starch grains among
thylakoids and around the pyrenoid. Around the apical division ring under
development smooth endoplasmic reticulum and numerous dictyosomes appeared surrounding
mitochondrial profiles. The cell wall was thick, electron dense and with an
external layer of mucilage. There was a clear fracture zone at the level of the
division ring. During vegetative mitoses the nucleolus disappeared and
numerous perinuclear dictyosomes appeared. After cytokinesis the thin wall
between the basal cell and the contiguous antheridium presented plasmodesmata. The side walls of the antheridia were thinner than the
traverse walls. The antheridial nucleus lacked a nucleolus and the antheridial
cytoplasm showed abundant perinuclear dictyosomes and a reticulate mitochondrion.
During gametogenesis both gametes gradually decreased
their cell volume simultaneously. The antheridial space was filled with
mucilage, which became condensed and electron dense between the two gametes. Mature
gametes had an apical dome with numerous spherical vesicles and a flagellar
apparatus with 8-10 axonemic basal bodies. The cytoplasm showed a large reticulate
mitochondrion and a reduced chloroplast.
The whole process in O. macrandrium is similar to that of Bulbochaete hiloensis with a remarkable difference. In the latter,
a phycoplast and a cell plate occur between the gametic nuclei of each
antheridium and a true wall between gametes is produced. In O. macrandrium and O. pluviale only condensed mucilage appeared
between gametes.