Cytoembryological studies on Paeonia peregrina L. - Journal of Cell ...

86 Recep Öztürk and Meral Ünal
Material and Methods
The flower buds were collected from the natural
population at ‹spartakule and were fixed in aceticalcohol
(1:3). Sections were cut at 7-10 µm and stained
with Regaurd’s haematoxylin. The aceto-orsein squash
method was also used in the study of
microsporogenesis. KI+I was applied to the sections to
identify starch grains in the embryo sacs.
Results
The anther wall and the divisions in the tapetal cells
The anther of Paeonia peregrina is tetrasporangiate.
The anther wall consists of epidermis, endothecium,
middle layers and tapetum. The single –layered
epidermal cells become stretched during the
maturation of anther. Endothecial cells do not show
any thickenings. The cells of middle layers are crushed
during the development. The cells of secretory tapetum
are large and have dense cytoplasm. They are
uninucleate in the early stage of development but the
mitotic division is not followed by cytokinesis (Figure
1 a-e). As a result, two-nucleated tapetal cells are
Figure 1: Nuclear divisions in the tapetal cells of Paeonia
peregrina. a. Prophase; b. Metaphase; c. Anaphase; d.
Telophase; e. Binucleate cell; f.-h. Irregular anaphase; i.
Prophase in binucleate cell; j. Metaphase in binucleate cell ;
k,l. Anaphase in binucleate cell; m,n. Fournucleate cell; o,
Nuclear fusion.
produced. Diploid chromosome number is 10 but
tapetal cells with 20 chromosomes were also seen. The
second mitotic division was observed resulting fournucleated
cells (Figure 1 i-n). Very often, due to the
fusion of nuclei become polyploid (Figure 1 o). The
following irregularities in the first and second mitoses
were noticed: lagging chromosomes, chromosome
bridges, fragments, unequal distribution of
chromosomes (Figure 1 f-h, k,l). Nuclear fusions were
frequently occurred resulting to the occurrence of
large, irregular shaped giant nuclei with many
nucleoli. Multinucleate tapetum degenerates at the
time of separation of the microspores from each other.
Microsporogenesis
In the majority of pollen mother cells (PMC) the
meiotic division (microsporogenesis) undergoes
normally (Figure 2 a-p). 5 bivalents were observed at
diakinesis (Figure 2 g). Cytokinesis is of simultaneous
type. The microspore tetrads are of isobilateral and
tetrahedral type. The microspores in tetrad are
surrounded by a thick callose wall.
In some PMCs 10 bivalents were seen at diakinesis
(Figure 3 a). Thus, both diploid and tetraploid
chromosome number were counted. Some meiotic
irregularities such as chromosome bridges, univalents
and multivalents, lagging chromosomes, fragments
were recorded in less number of PMCs of the diploid
and tetraploid forms (Figure 3 b,c ) As a result of
irregularities pentads and hexads were detected.
Megasporogenesis and Megagametogenesis
The ovary has 16 anatropous ovules placed along the
ventral wall. The ovules are bitegmic and
crassinucellate.
The archesporium is multicellular. The 3 or 4
archesporial cells differentiate in nucellus and become
prominent with their dense cytoplasm and large nuclei
(Figure 4 a). One of them functions as a megaspore
mother cell (MMC) and undergoes meiosis
(megasporogenesis). Before meiosis the size of MMC
increases. 5 bivalents were counted at metaphase I
(n=5) (Figure l b). Cytokinesis is of the successive
type. As a result of first meiosis, the two dyad cells are
produced; the chalazal one is larger than the other
(Figure 4 c) The megaspore tetrad is linear or T-shaped
(Figure 4 d)
The chalazal megaspore is functional while the