| Summary: | 碩士 === 國立臺灣大學 === 植物學系 === 86 === Abstract
The changes of staminate flower and pollen during
different developmental stages of Luffa cylindrica (L.) Roem
were studied with light microscope, scanning and transmission
electron microscope.
Floral primodium initiated from infloresence primodium in
a spiral order. Five sepal primodia intiated from the edge of a
floral primodium in a spiral order, too. Then five petal
primodia arised simultaneously in a whorl arrangement, followed
by five stamen primodia. Consequently, the stamen grew up and
developed a curved anther.
The anther wall layers occurred as dicotyledonous type and
were composed of epidermis, endothecium, middle layers (2 ~ 3
layers) and tapetum. Sporogenous tissue was derived from the
inner layer, which was resulted from periclinal division of the
hypodermal layer.
Callose wall was deposited between the plasma membrane and
cell wall of microspore mother cells before meiosis. The
cytokinesis after meiosis occurred simultaneously by the
centripetal invasion of callose wall, then a tetrahedral tetrad
enclosed in the callose wall was produced.
After callose wall was dissolved, four microspores were
released into anther loculus. At the same time, tapetal cell
wall was disintegrated, and deposition of lipid droplets
started in tapetal cytoplasm. Deposition of lipid droplets also
occurred in the cytosol of microspores during the middle and
late microspore stage.
Haploidal mitosis of microspore took place, which resulted
in a big vegetative cell and a small generative cell. Mature
pollen grains contained two kinds of reserves, lipid droplet
and starch grain; the former was produced in the cytosol and
the latter was deposited inside the amyloplasts.
The secretory tapetum reached its optimal activity from the
late tetrad to early microspore stage. Two organelles involved
in production of lipid droplets were smooth endoplasmic
reticulum (SER) and elaioplast. As tapetal cytoplasm
degenerated, clusters of lipid droplets that were deposited
within the cytosol and elaioplast moved towards the pollen
grain. At anthesis, pollenkitt derived from tapetum were coated
on the surface of the mature pollen grain.
Development of pollen wall started during the early tetrad
stage. At the beginning, a fibrillar material was deposited
between the callose wall and plasma membrane of microspores.
The primexine was then accumulated on the position where
fibrillar material possessed. Subsequently, exine material
secreted by microspore itself was accumulated on the same
position to replace primexine. The tectum and bacule had been
formed before the discontinuous foot layer was visible. There
were two distinguishable laye
in endexine. The outer one seemed to be formed after the
appearance of white lines which was just beneath the foot layer
at the late tetrad stage, and the inner one was formed after
dissolution of callose wall and composed of a number of
sporopollenin-like granules. At the late microspore stage that
was just before the haploidal mitosis of microspore, the intine
was formed under the endexine at aperatural zone. After
mitosis, the formation of intine finished around the pollen
grain beneath the inner endexi
. There were three layers in the intine of aperatural zone.
Fibrillar material between the bacules and intine showed
PAS positive reaction. Besides PAS, the intine of aperatural
zone also showed Coomassie blue positive reaction.
The results of this study present a detailed information
about the microsporogenesis and pollen wall development of
Luffa cylindrica (L.) Roem, and ascertained that exine was
derived from a combined contribution from tapetum and
microspore, rather than from either of them. We presumed that
the control of exine pattern has been determined in the
microspore mother cell.
IV
|
|---|
