Transcript of "Bio 130 microsporogenesis gametogenesis 2013"
formation of spores
microspore into the
the pollen grain
containing sperm cells
Ontogeny of the anther
Development and differentiation of sporogenous tissue
Structure of pollen
Events in anther development
name for all stamens
In a flower.
Anther- for pollen
Filament- support, nutrient
transport , pollen dispersal
filaments forms a flexible
swivel joint, causes anther
to flutter and shake out
Longitudinal cutaway view
of a cherry flower
Development of anther
Hypoderm-found beneath protoderm and
becomes archesporial layer. Divides into:
1. Pri parietal cells
(outer)- differentiates into sporangial
outer wall- --endothecium and tapetum
2. Primary sporogenous cells- microsporocytes
restricted to four
corners of the
The cellular events of stamen
•contributions from hypodermal
layer in some
•with accompanying anticlinal
activity from protoderm and a
little from outer corpus.
A. Before emergence.periclinal div. of corpus cells at stamen site
B. An emergent stamen. Periclinal div of corpus cells but not the hypd.
C. Tangential div. of emergent stamen.
D. Emergent stamen with recent anticlinal div. of hypodermal cells and
anticli. and periclinal div of corpus. E. adjacent section in hypodermal
cells, F. predominance of anticl div. in hypodermis-derived cells
Anther divides. Periclinal division takes place in the first
layer called archesporial layer) beneath protoderm.
Archesporial layer gives rise:
1.Outer primary parietal layer: gives rise to 2 or 3 layers
A. future endothecium b. middle layer c. tapetum
2.Inner primary sporogenous cells. Divides by mitosis or directly function as
Wall layers microsporocytes
ANTHER WALL LAYERS
A. Anther primordium
B. Archesporial layer next to
C. Mitotic div. in archesp layer
forms primary parietal
D. Division in the PPL (see
arrow) gives rise to 2
E. Inner PPL differentiates
into outer Tapetum. Outer PPL
differentiates into the sec.
Additional mitotic division of
outer PPL gives rise to
Endothecium and Middle
Stamen growth and
Differentiation- early stages
Sex Plant Reproduction (2011) 24:307-317
Early stages continued
F. Structural organization of
anther wall is complete prior
to microspore mother cell
formation. Ep epidermis, Ed
endothecium, M middle layer,
To outer tapetum, Ti inner
tapetum, S sporogenous cells
G. Microsporocyte begin to
differentiate and enclosed by
tapetal cells. Tapetal cells
divide anticlinally and
periclinally. Most have 2
H. Microsporocyte at pre-
Pair and exchange
up by homologous
Each pair of
cells form, each
consists of two
Leptotene- chromatin condenses, preceded by DNA replication
Zygonema-homologous chromosomes pair form bivalents
Pachytene-physical exchange of chromosome parts occurs bet
Diplotene- partial separation
of each of sister chromatids
from their homologous
Diakinesis- homologs are held
together by chiasmata at their
Summary: ist meiotic prophase- replicated homologous
chromosomes synapse, usually undergo crossing-over, then
condense as tetrads. Held together at the centromeres, pairs of
Sister chromatids in each tetrad are ready to be distributed to
opposite .poles during the remainder of the first meiotic division
plate. Due to
Meiosis I, each
Separate, move to
opposite poles as
Telophase II and
Cytokinesis. Nuclei form.
A Pachytene, D. Metaphase
B. Diplotene E. Anaphase
C. diakinesis F. Telophase
(cell plate not formed yet)
A. Late interphase in the dyad
B. Metaphase II E.tetrads
C. Anaphase II F. Post meiotic
D. Telophase II microspore
Pollen development before
A.Microsporocytes prior to meiosis. Clear
boundary is callose.
B. Pitlike structures within callose wall
C. Karyokinesis prior to cytokinesis..thus
haploid nuclei. Callose remains distinct
D. Primexine (note protrusions) surrounds the
protoplast of each tetrad microspore
E. Tetrad of microspores enveloped in thick
F.Microspores within tetrads round up,
numerous vacuoles present. Future aperture
developed. Nucleus centrally located.
G. Cell wall continues to thicken.
Outermost portion of wall called exine : has 2
wall layers:1. ectexine
2. endexine-smooth layer surrounds protoplast
H. Walls are more prominent
I. Large vacuoles in microspores before gameto
Pollen development Continued A. Highly vacuolated
microspore,nucleus near wall
B. Ist pollen mitosis shows
generative cell (arrow)
C. veg. cell moves next to gen.
D. Generative cell detaches from
wall and moves into cytoplasm
of veg cell.
E. Cytoplasm of veg cell is
dense with prominent nucleus.
Generative cell enclosed by its
own membrane, cell has
vacuoles. Aperture is a
Pollen development Continued F. Pollen grain has copious
G.DAPI-stained pollen reveals
location of gen cell nucleus at
time of sperm formation
H. DAPI stain reveals elongated
sperm cell nuclei close together
I. Sperm appearing as 1
structure. J. wall is well-defined
A. Sporogenous or archesp cells, after
last mitotic division, each secretes
callose, B.Four sacs of one anther
to show mmc surrounded by callose
C. Before cytokinesis. Coenocytic
tetrads during furrowing
D. Microspores separated but
still retained as tetrad for some
Glandular or secretory tapetum-
cells remain in their
the sac and later disintegrate and
absorbed by pollen
Amoeboid or invasive
Flows amoeba-likeinto the sac
interior after callose dissolves
and engulfs the separated
E. Late vacuolate microspores above degenerating tapetum
F. Partly engorged pollen with nucleus of vegetative and generative cells
G. Mature engorged pollen in sacs. Tapetum is gone. Endothecium has wall bars.
In A tapetum is still intact and microspores embedded in callose,
in B the tapetum intrudes into the sac , c. microspores surrounded by
invasive tapetum. In D. microspores engulfed by tapetum,
In E, invasive tapetum disappears.
Cells lining the anther lumen
– a layer known as the
endothecium – secretes
materials that are essential
for the proper maturation of
the pollen grains.
Roles played by tapetum
1.Nourishment of the developing pollen mother cells
2. Formation of exine
3 . Deposition of tryphine on the pollen wall
4. Secretes enzymes that dissolves the callose surrounding
tetrads . In some species e.g. sweet pepper
Pollen from different
species, variation in exine
Telophase of microspore mitosis in African lily. Most
organelles are unequally segregated. Plastid is dividing
adjacent to the chromatin of the future vegetative cell but no
plastids occur between cell plate and chromatin of the future
Post-meiosis: internal microspore/pollen events
After a microspore enlarges in volume, unequal
partitioning of cytoplasm takes place, it divides
mitotically to form:
small lens to spheroidal shaped generative cell
pressed against the vegetative cell membrane
The generative cell moves away from the wall and into
the interior of the vegetative cell after callose dissolves.
Thus, one cell is completely surrounded by another cell.
Generative cells typically become ovate to elongate
while in the pollen grain. Lack plastids, before
microspore mitosis, the plastids usually migrate to
an area of the vegetative cell away from where the
future generative cell will form.
B. Post-mitotic pollen grain with vegetative cell and
newly-formed generative cell.
C. Large central vacuole and generative cell appressed
D. Pollen grain and generative cell have enlarged.
E. Generative cell in mitosis
F. Binucleate generative cell appressed to pollen wall
G. Two sperm cells still attached to each other but free from
pollen wall; pollen engorging but central vacuole
H. Mature engorged pollen grain with separated lenticular
sperm cells embedded in vegetative cell.
Plastids in generative cell or sperm cells are uncommon.
No plastids in 18 grass species (includes common cereal
None in any of the 7 crucifers (Brassicaceae) tested
among 39 legumes, 9 species had plastids.
Pollen of most species shed from the anther with just
generative and a vegetative cell.
A sample of 2,000 dicots and monocots showed 30%
Cross-section of mature lily anther just before it dehisces
at the stomium
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