Megasporogenesis and microsporogenesis
megasporocyte microsporocyte
Generates megaspore and microspores
meiosis
REVIEW
Examples of angiosperm diversity in pollen and stigma structures
A.Hydrated Lilium longiflorum pollen grain. Red stained h...
The exine protects the spore against dessication,
mechanical pressure and ultraviolet radiation. Sometimes
the exine layer...
A. Pollen tetrad from Arabidopsis mutant quartet. Four complete pollen grains connected by
exine bridges
B. Fused pollen g...
The exine protects the spore against dessication,
mechanical pressure and ultraviolet radiation. Sometimes
the exine layer...
Pollen outer surface
Outer exine- multilayered ,
sporopollenin, interrupted
by apertures
Inner intine- sometimes
multilaye...
Pollen tube
Stigma- receptive part of pistil,
bind pollen ,mediate tube
migration into style:
Receptive stigma are of 2
ty...
Stigma papillae
from Arabidopsis
Dry- intact surface cells,
protrusion as papillae and
cells covered with cell wall,
waxy ...
stigma
Pollen-stigma functions
1. Initial adhesion: exine-mediated
May depend on biophysical or
chemical interactions betw...
D. Pollen coat has mobilized to the site of contact between pollen
and the stigma forming a foot between the 2 surfaces
B. Pollen hydration: Activating metabolism.
Pollen highly dessicated: 15 to 35 % water content when released
from anthers....
C. Pollen polarization and germination: preparing for
pollen tube growth
Hydration transforms a pollen from non-polar cell...
Germination of pollen tube
Pollen tubes
extend up to sev.
cm to reach
embryo sac. Cell
wall lacks
cellulose but has
anothe...
Cytoplasmic domain
A Clear zone--------------------devoid of large organelles, no organized
movement
B Subapical domain
C....
A. Tip domain- rich in Golgi vesicles
B. Sub-apical domain- with metabolically active organelles:
mitochondria, dictyosome...
• Secretory vesicles originate from the Golgi network and are
transported over the actin cytoskeleton into the growing tip...
 Cytoplasm continues to move with
the tip as tube elongates
 Cytoskeleton continually transports organelles, the
generat...
• Golgi/dictyosome-derived vesicles containing callose
(not cellulose) transported to tip by microfilaments.
Vesicles fus...
pollination
POLLEN TUBE GUIDANCE ON THE PISTIL
1. THRU PAPILLA
CELL WALL OF DRY
STIGMA OR
INTERCELLULAR
SPACES
2. BETWEEN CELLS
IN SEC...
A. Porogamy (pollen directed to the micropyle by molecular
signal
B. Chalazogamy ( pollen adhere and grow up the surface o...
porogamy
chalazogamy Mesogamy
(thru funiculus)
Entry of pollen tube in the embryo sac is under chemotropic guidance
(synergids have filiform apparatus and secrete some c...
Pollen tube discharge: includes 2 sperms, the veg, nucleus and a
fair amount of cytoplasm. A portion of cytoplasm is retai...
Tube enters at the apex of the filiform apparatus
and after growing, it arrives in the cytoplasm of the
synergid. The pene...
Synergids “ synergos”- working together
Coined by Eduard Strasburger 19th
century botanist (Vesque, 1878)
filiform apparat...
Megaspore mother cell devs. from surrounding nucellar
tissue and undergoes meiotic division to form megaspore.
Nucellus co...
Pollination
Double fertilization
Pollen stigma interaction
Upcoming SlideShare
Loading in...5
×

Pollen stigma interaction

1,930

Published on

Published in: Technology, Business
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
1,930
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
144
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide
  • Where tapetal coatings of pollen
  • rafa
  • Transcript of "Pollen stigma interaction"

    1. 1. Megasporogenesis and microsporogenesis megasporocyte microsporocyte Generates megaspore and microspores meiosis REVIEW
    2. 2. Examples of angiosperm diversity in pollen and stigma structures A.Hydrated Lilium longiflorum pollen grain. Red stained has several fissures at the single aperture . Green coating (green) forms droplets on the surfaces of the ornamented exine walls B.Multiapertured pollen of Passiflora fanguinolenta C.Polyad pollen of Acacia retinoides D.Several pollen types E.A portion of stigma of Torenia fourmiere F.Stigma papillae of Arabidopsis D
    3. 3. The exine protects the spore against dessication, mechanical pressure and ultraviolet radiation. Sometimes the exine layer is covered by sticky substances (pollenkitt, tryphine, elastoviscin and sporopollenin viscin threads), which are also produced by the tapetum. Pollenkitt- an adhesive material facilitates the attachment of pollen grains to insects, and in this way also zoophilic pollination. It also plays an important role in the adhesion of pollen grains to the female stigma and in the recognition between pollen and pistil. Also substances responsible for pollen allergy are often products originating from the tapetum. Pollen grains
    4. 4. A. Pollen tetrad from Arabidopsis mutant quartet. Four complete pollen grains connected by exine bridges B. Fused pollen grains of Arabidopsis mutant tes/stud. Cytokinesis does not occur after meiosis resulting in multinucleate cytoplasm c. Natural pollen tetrads from Drocera binata
    5. 5. The exine protects the spore against dessication, mechanical pressure and ultraviolet radiation. Sometimes the exine layer is covered by sticky substances (pollenkitt, tryphine, elastoviscin and sporopollenin viscin threads), which are also produced by the tapetum. Pollenkitt- an adhesive material facilitates the attachment of pollen grains to insects, and in this way also zoophilic pollination. It also plays an important role in the adhesion of pollen grains to the female stigma and in the recognition between pollen and pistil. Also substances responsible for pollen allergy are often products originating from the tapetum. Pollen grains
    6. 6. Pollen outer surface Outer exine- multilayered , sporopollenin, interrupted by apertures Inner intine- sometimes multilayered with cellulose Pollen coat- lipids, proteins pigments, aromatic compounds fill the sculptured cavities of exine., Pollen-stigma interaction 3 strata ( relative amount varying between species C
    7. 7. Pollen tube Stigma- receptive part of pistil, bind pollen ,mediate tube migration into style: Receptive stigma are of 2 types: Wet- covered with surface cells , often lyse & release secretions. Pollen simply sinks in the viscuous fluid.
    8. 8. Stigma papillae from Arabidopsis Dry- intact surface cells, protrusion as papillae and cells covered with cell wall, waxy cuticle and proteinaceous pellicle.. Never has copious surface secretion. Possibilility for pollen attraction and retention is adherence by chemical bonds. Ex. A chemical bond forms where the exine contacts the pellicle or where tapetal coatings on exine flows on the stigma surface.
    9. 9. stigma Pollen-stigma functions 1. Initial adhesion: exine-mediated May depend on biophysical or chemical interactions between stigma surface and exine polymers 2.Mobilization of pollen coat leads to mixing of lipids and proteins and form “foot” of contact on stigma surface. 3. Later stage: Proteins and lipids on pollen coat and proteins on stigma surface contribute to adhesion, requires protein- protein interaction A. Pollen adhesion
    10. 10. D. Pollen coat has mobilized to the site of contact between pollen and the stigma forming a foot between the 2 surfaces
    11. 11. B. Pollen hydration: Activating metabolism. Pollen highly dessicated: 15 to 35 % water content when released from anthers. On wet stigmas water immediately surrounds pollen grains On dry stigmas pollen mobilize their lipid coat to form an interface between the two surfaces. This interface will promote water flow. water nutrients, etc. Transported rapidly into the grain from stigma exudate (wet stigma ) or from stigma papillae from dry stigma Aquaporins expression in the stigma : water channels involved in the rapid but regulated water release from stigma to pollen Aquaporins are transport proteins that facilitate water transport across membranes
    12. 12. C. Pollen polarization and germination: preparing for pollen tube growth Hydration transforms a pollen from non-polar cell to highly polarized cell. Within minutes after hydration pollen organizes its cytoplasm and cytoskeleton structures to support extension of a single tube:  Formation of filamentous cytoskeletal structures that wrap around the nuclei  Actin cytoskeleton polarization toward the site of tube emergence  Reorientation of large vegetative nucleus so that it enters the extending tube before the generative cells  Assembly of mitochondria and polysaccharide particles at the site of elongating tube tip  Selection of pollen plasma membrane for secretory vesicle targeting and deposition of callose at site of tube emergence
    13. 13. Germination of pollen tube Pollen tubes extend up to sev. cm to reach embryo sac. Cell wall lacks cellulose but has another polysaccharide- callose- , a glucan Callose –synthesized by Golgi and transported to the extreme tip of pollen tube by Golgi-derived vesicles .Fusion of vesicles with plasma membrane expand the cell membrane of elongating tube Content of vesicles expand the wall of elongating tube
    14. 14. Cytoplasmic domain A Clear zone--------------------devoid of large organelles, no organized movement B Subapical domain C. Nuclear domain D. vacuolar domain Pollen tube elongation up to many cm thru female tissues Pollen tubes are polarized cells. Internal differentiation with distinct intracellular zones
    15. 15. A. Tip domain- rich in Golgi vesicles B. Sub-apical domain- with metabolically active organelles: mitochondria, dictyosomes, ER, vesicles C. Nuclear domain: large organelles and male germ unit D. Vacuolar domain. Enlarges as the tube grows.
    16. 16. • Secretory vesicles originate from the Golgi network and are transported over the actin cytoskeleton into the growing tip where they fuse with the tip membrane expanding the wall and the plasma membrane. • Besides pollen tube wall proteins, these transport vesicles contain pectins as part of the primary tube tip wall. • Total cytoplasmic vol. does not increase as pollen tube grows; bulk of cytoplasm is in close proximity to growing tip Germinating pollen
    17. 17.  Cytoplasm continues to move with the tip as tube elongates  Cytoskeleton continually transports organelles, the generative or sperm cells and vegetative nucleus toward growing tip  Shows “reverse fountain” cytoplasmic streaming-forward movement of organelles thru cortical region of the tube, undergoes a turnover in the subapical domain moving back centrally, away from the tip of the tube.
    18. 18. • Golgi/dictyosome-derived vesicles containing callose (not cellulose) transported to tip by microfilaments. Vesicles fuse with plasma membrane at tip of tube so expands the wall contents of vesicles expand the plasma membrane as the tube grows vesicles
    19. 19. pollination
    20. 20. POLLEN TUBE GUIDANCE ON THE PISTIL 1. THRU PAPILLA CELL WALL OF DRY STIGMA OR INTERCELLULAR SPACES 2. BETWEEN CELLS IN SECRETORY REGIONS OF WET STIGMAS. 12hrs 24 hrs 6d
    21. 21. A. Porogamy (pollen directed to the micropyle by molecular signal B. Chalazogamy ( pollen adhere and grow up the surface of chalazal region. C. Mesogamy (pollen directed to the micropyle by molecular signals from synergids)
    22. 22. porogamy chalazogamy Mesogamy (thru funiculus)
    23. 23. Entry of pollen tube in the embryo sac is under chemotropic guidance (synergids have filiform apparatus and secrete some chemicals). Once inside the cytoplasm of the synergid, pollen tube growth stops, tip ruptures, release the 2 sperm. One of the synergid cells begin to degenerate as pollen tube enters it. Release of pollen tube contents into the synergid : A. Showing two male gametes and a degenerating vegetative nucleus near the filiform apparatus, B. Release of male gametes inside the synergid, C. Movement of male gametes towards the egg nucleus and into the central cell.
    24. 24. Pollen tube discharge: includes 2 sperms, the veg, nucleus and a fair amount of cytoplasm. A portion of cytoplasm is retained in the pollen tube. No mixing between cytoplasm released by the pollen tube and that of the synergid. They remain as two separate entities.
    25. 25. Tube enters at the apex of the filiform apparatus and after growing, it arrives in the cytoplasm of the synergid. The penetrated synergid starts degenerating before the arrival of the pollen tube, but after pollination. The process of discharge takes place in seconds. Degenerating synergid filiform- specialized region of the synergid cell wall
    26. 26. Synergids “ synergos”- working together Coined by Eduard Strasburger 19th century botanist (Vesque, 1878) filiform apparatus Increases surface area of plasma membrane in the region, also associated with elaborate ER Synergids begin to degenerate as pollen tube enters it or shortly Pollen tube guidance (shown by laser ablation techniques to selectively remove different cells within the female gametophyte) Mediates transport of molecules into and out of synergids Necessary for the cessation of pollen tube growth and release of sperm cells. MYB98 protein- functions as regulator of genes expressed in synergids required for formation of filiform apparatus, Mutants myb98 show defects in pollen tube guidance and dev of filiform apparatus
    27. 27. Megaspore mother cell devs. from surrounding nucellar tissue and undergoes meiotic division to form megaspore. Nucellus considered as a megasporangium funiculus chalaza- region where integuments fuse with funiculus
    28. 28. Pollination Double fertilization
    1. A particular slide catching your eye?

      Clipping is a handy way to collect important slides you want to go back to later.

    ×