1. Faculty of Science, School of Sciences, Natabua Campus Lautoka
BIO706 Embryology Lectures 14: Micro and mega-sporangium

2. in nonvascular plants gametophyte is dominant, sporophyte is visible
in seedless vascular plants, sporophyte is dominant, gametophyte is visible
in seed plants – gymnosperms and angiosperms, sporophyte is increasingly dominant, gametophyte is enclosed in the sporophyte

3. homosporous plants
one kind of sporangia;
one kind of spore; one kind of gametophyte;
each gametophyte can produce both eggs and sperm

4. megasporangia megaspores mega-gametophytes
Seed Plants are heterosporous plants:
have two kinds of sporangia
megasporangia megaspores mega-gametophytes
microsporangia microspores micro-gametophytes
* megagametophytes produce eggs;
microgametophytes produce sperm

5. Megasporangia, megagametophytes, and eggs
megasporangia are located within larger ovules
- each ovule consists of integuments,
a nucellus (the megasporangium), and a funiculus
micropyle

6. produces megaspores enclosed in the ovule
megasporogenesis - one or more cells in the nucellus (megasporocytes) undergo meiosis;
produces megaspores enclosed in the ovule
megasporocyte (haploid) megaspores (diploid)
nucellus (diploid
integument (diploid)

7. produces a megagametophyte (multicellular, haploid)
- megaspore germinates in the nucellus,
produces a megagametophyte (multicellular, haploid)
- megagametophyte will produce at least one egg (haploid)
(the process = megagametogenesis)
egg
megagametophyte
nucellus
integument

8. Microsporangia, microgametophytes, and sperm
microsporangia consist of
sporogenous tissue (microsporocytes) and a microsporangium wall

9. Sporangium sporangium
microsporocytes (2n) microspores (1n) meiosis
Sporangium sporangium

10. microgametogenesis:
microspore (1n) microgametophyte germination (mitosis)
- the microgametophyte is very small and enclosed in cell wall of a single microspore = a pollen grain

11. cells of the sporangium wall have diploid nuclei
MICROSPORANGIUM
microsporocytes (cells of the sporogenous tissue) have diploid nuclei
microspores each have a haploid nucleus
each pollen grain is made up of a few cells, each with a haploid nucleus
each pollen grain (microgametophyte) produces at least two
sperm and carries them to an ovule for fertilization

12. microsporangium opens to release pollen grains = dehiscence
pollen grains are dispersed, landing near an ovule = pollination
pollen grain germinates, producing a pollen tube

13. pollen tube grows to the egg cell;
sperm travel through pollen tube, are released near egg
egg
megagametophyte
nucellus
integument
** POLLEN TUBE ELIMINATES THE NEED TO SWIM THROUGH EXTERNAL WATER

14. - fertilization of egg zygote (unicellular, diploid)
zygote embryo (multicellular, diploid)
embryo is enclosed in the ovule
embryo (2n)
megagametophyte (1n)
nucellus (2n)
Integument 2n

15. hardening of the integuments produces a seed
- hardened integuments = seed coat
- interior contains:
the embryo (offspring sporophyte), and nutrition (stored in nucellus or other tissue)
seed coat
embryo
nutrition
seed

16. seeds provide many adaptive advantages to plants:
1) protection
2) carries nutrients
3) offspring dispersal

17. STAMEN, MICROSPORANGIUM
AND POLLEN GRAIN
Microspores matures into pollen grains
Pollen grains, which contribute the male gamete, are form within an anther
Anthers may be monothecal (two lobes or sporangia) or mostly bithecal (four lobes or sporangia)

18. Anther type
Bithecal Anther

19. Pollen producing reproductive organ of flower.
STAMEN
Pollen producing reproductive organ of
flower.
They consists of a stalk – filament
and anther which contains
microsporangia.
Most anthers are 2 lobed, attached
to filament at base or to the center.
Sterile tissue between lobes –
connective. Anther has 4 microsporangia

21. Anther has 4 microsporangia.
This forms sacs in anther.
Each microsporangium
lined with nutritive tissue - Tapetum,
it contains diploid pollen mother cells.

22. Flower and its parts

23. These cells undergo meiosis to form haploid spores.
Spores remain attached to each other
or separate
Each microspore divides mitotically
to form immature microgametophyte called as – pollen grain.

24. Pollen released through opening of anther
Pollen released through opening of anther. Pollen is carried by external agent like wind, water, insects etc and are pollinated.
After pollination, pollen continues it's development inside pollen tube. Undergoes mitosis to produce 2 male gametes.

25. REMEMBER - Stamens in flower collectively called – Androecium
REMEMBER - Stamens in flower collectively called – Androecium. It forms whorl around surrounding gynoecium. Column formed by fusion of multiple filaments is called – androphore. Some flowers have both male and female sexual organs. Some don't. Flowers with only stamens – androecious. Flowers with only carpels – gynoecious

27. MICROSPORANGIUM
It's a sporangium that produces spores which give rise to male gametophytes.
Microsporangium produces microsporocytes.
It is also called as microspore mother cell.
This creates 4 microspores through meiosis.
Microspores divide to create pollen grains.

28. POLLEN GRAINS
Pollen is fine to coarse powder containing microgametophytes of seed plants which produce male gametes.
Pollen grains have hard coat – protects the sperms cells.
When pollen is on the pistil, it germinates to produce pollen tube.
Tube transfers sperm to ovule.

29. Pollen not a male gamete.
Each pollen has vegetative and
generative cell.
This contains 2 nuclei -
1) Tube nucleus – produces pollen tube.
2) Generative nucleus – divides to form 2 sperm cells.
Pollen produced in microsporangium.
They come in different sizes.

31. Anther composed of mass of cells – it is undifferentiated.
As flower develops 4 groups of sporogenous cells develop within anther.
Fertile cells surrounded by sterile cells that grow into wall of pollen sac.
Some cells grow into nutritive cells that provide nutrition.
Microsporogenesis – Process by which 4 haploid microspores are produced from each diploid sporangenous cell after meiotic division.

33. After formation of 4 microspores, development of pollen grain wall begins.
Pollen wall protects sperm nucleus.
Pollen grain surface covered with wax and proteins which are held in place by structures called as sculpture elements.
Outer pollen wall prevents pollen from shrinking and crushing the genetic material.

34. Pollen germination

35. Questions are welcome