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Megasporogenesis, Microsporogenesis and Development of Gametophytes in Eleutherococcus senticosus (Araliaceae)

LIU Lin-De, WANG Zhong-Li, TIAN Guo-Wei, SHEN Jia-Heng   

  • Received:1900-01-01 Revised:1900-01-01 Online:1998-07-10 Published:1998-07-10
  • Contact: LIU Lin-De

Abstract:

This paper describes megasporogenesis, microsporogenesis, and development of
female and male gametophytes in Eleutherococcus senticosus. The main results are as fol-
lows: Flowers of E.  senticosus are epigynous, pentamerous. Anthers are 4 -microsporan-
giate. An ovary has 5 loculi. Each ovary loculus has 2 ovules: the upper ovule and the lower
ovule. The upper one is orthotropous and degenerates after the formation of archesporial cell,
while the lower one is anatropous, unitegmic and crassinucellar, and able to continue devel-
oping. In male plants, microsporogenesis and development of male gametophytes took place
in regular way, but a series of abnormal phenomena were found in megasporogenesis and de-
velopment of female gametophytes. The microspore mother cells gave rise to tetrahedral te-
trads by meiosis. Cytokinesis was of the simultaneous type. The mature pollen was 3-celled
and shed singly. The anther wall formation belonged to the dicotyledonous type. At the
stage of microspore mother cell, the anther wall consisted of four layers, i.e. epidermis, en-
dothecium, middle layer, and tapetum. The tapetum was of glandular type and its most cells
were binucleate. When microspores were at the uninucleate stage, the tapetum began to de-
generate in situ. When microspores developed into 3-celled pollen grains, the tapetum had
fully degenerates. In the lower ovule of male flower, the megaspore mother cell gave rise to
a linear or “T” -shaped tetrad. In some cases, a new archesporial cell over the tetrad or two
tetrads parallel or in a series were observed. Furthermore, the position of functional megas-
pore was variable; any one or two megaspores might be functional, or one megaspore gave
rise to a uninucleate embryo sac, but two other megaspores also had a potentiality of develop-
ing into the embryo sac. In generally, on the day when flowers opened, female gameto-
phytes contained only 4 cells: a central cell, two irregular synergids and one unusual egg cell.
In female plants, microspore mother cells and secondary sporogenous cells were observed.
But at the stage of secondary sporogenous cell, the newly differentiated tapetum took the ap-
pearance of degeneration. Later, during the whole stage of meiosis, the trace of degenerative
tapetum could be seen. At last, the microsporangium degenerated and no tetrad formed. On
the blossom day, all anthers shriveled without pollen grains. In female flowers, megasporo-
genesis and development of female gametophytes were normal: the tetrad of megaspores was
linear or “T”-shaped; the chalazal megaspore was usually functional; the development of em-
bryo sac was of the Polygonum type. On the blossom day, most embryo sacs consisted of 7
cells with 8 nuclei or 7 cells with 7 nuclei; but the egg apparatus was not fully developed. In
hermaphroditic plants, microsporogenesis was normal but the development of male gameto-
phytes was partially abnormal. When the hermaphroditic flowers blossomed, there were more
or less empty pollen grains in the microsporangium and these pollen grains were quite differ-
ent in size. The development of most gynoecia was normal but numerous abnormal embryo
sacs could be seen. On the blossom day, female gametophytes were mainly 7-celled with 8-
nuclei or with 7-nuclei or 4-celled with antipodal cells degenerated; the egg apparatus was
not fully developed either.

Key words: Eleutherococcus senticosus, Megasporogenesis, Microsporogenesis, Male and fe-male gametophytes, Gametophyte development

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