1. Faculty of Science, School of Sciences, Natabua Campus Lautoka BIO706 Embryology Lectures 21:Flowering Plant Reproduction - I

2. QUESTIONS WE TRY TO ANSWER:
How does a single cell become a complex organism?
What mechanisms / factors control development?
Cell fate in order to produce a functional plant?
Plant development

3. Angiosperm development alternation of generations
diploid phase = sporophyte
embryogenesis, germination, primary and secondary development
vegetative & reproductive development
juvenile & adult phase, a phase change
haploid phase = gametophyte
megaspore  female gametophyte
microspore  male gametophyte

4. Gametophyte development
female gametophyte = embryo sac
-carpels: ovary, style & stigma
-ovules: nucellus, integuments, micropyle
male gametophyte
-microspore mother cells surrounded by tapetum  meiosis  microspores  pollen grains

5. Sexual life cycle of an angiosperm

6. Flower and its parts

7. Meiosis occurs in sporangia of sporophytes
Angiosperms
Key
Haploid
Diploid
Microsporangium
Microspore
Alternation of Generations
Meiosis
Sporophyte
Meiosis
Meiosis occurs in sporangia of sporophytes
Megasporangium
Gametophytes
Megaspore
Fertilization

8. Spores divide by mitosis and develop into mature gametophytes
Angiosperms
Key
Haploid
Diploid
Microsporangium
Microspore
Alternation of Generations
Meiosis
Pollen
Sporophyte
Spores divide by mitosis and develop into mature gametophytes
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo sac
Fertilization

9. Alternation of Generations
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Pollen
Sporophyte
Specialized gametophyte cells divide by mitosis to form gametes
Meiosis
Megasporangium
Gametophytes
Megaspore
Embryo sac
Egg
2 sperm
Fertilization

10. Alternation of Generations
Angiosperms
Key
Haploid
Diploid
Microsporangium
Alternation of Generations
Microspore
Meiosis
Pollen
Sporophyte
Seedling
Meiosis
Megasporangium
Gametes fuse during fertilization to produce a zygote
Gametophytes
Megaspore
Embryo
Embryo sac
Egg
Zygote
2 sperm
Endosperm
Fertilization

11. A sporophytes’ male reproductive structures:
Stamen
Anther
Filament

12. A sporophytes’
male
reproductive structures:
Each anther contains multiple pollen sacs (microsporangia)

13. A sporophytes’
male
reproductive structures:
Each pollen sac contains mutiple diploid microsporocytes (microspore mother cells)

14. A sporophytes’
male
reproductive structures:
Each microsporocyte divides by meiosis to produce 4 haploid microspores

15. A sporophytes’
male
reproductive structures:
Each microspore divides once by mitosis to form an immature male gametophyte (pollen grain)
A single tube cell encloses a single generative cell

16. reproductive structures:
A sporophytes’
male
reproductive structures:
The pollen grain matures into an adult male gametophyte when its generative cell divides by mitosis to produce two sperm
The adult male gameto-phyte is a fully mature, indepen-dent plant with only 3 cells

17. A sporophytes’ female reproductive structures:
Carpel
Stigma
Style
Ovary
Ovule
Receptacle

18. A sporophytes’ female reproductive structures:
Each ovule contains a megasporangium
Each megasporangium contains a megasporocyte (megaspore mother cell)

19. A sporophytes’ female reproductive structures:
A megasporocyte divides by meiosis to form 4 cells
Only 1 of the 4 cells survives: the megaspore

20. A sporophytes’ female reproductive structures:
The megaspore’s nucleus divides 3 times:
giving 1248 nuclei
Membranes then partition the 8-nucleate immature gametophyte cell into 7 smaller cells (one with 2 nuclei)

21. A sporophytes’ female reproductive structures:
The 7 cells:
1 egg
1 cell with 2 polar nuclei
5 other cells
The 7 cells comprise the mature, completely dependent female gametophyte (embryo sac)

22. A pollen grain disperses to a stigma
Double fertilization of angiosperms (and independently derived in a few gymnosperms)
A pollen grain disperses to a stigma
(pollination)
The tube cell grows into a pollen tube

23. The 2 sperm cells travel down the pollen tube to the embryo sac
Double fertilization of angiosperms (and independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to the embryo sac

24. The 2 sperm cells travel down the pollen tube to the embryo sac
Double fertilization of angiosperms (and independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to the embryo sac

25. The 2 sperm cells travel down the pollen tube to the embryo sac
Double fertilization of angiosperms (and independently derived in a few gymnosperms)
The 2 sperm cells travel down the pollen tube to the embryo sac

26. 1 sperm fuses with the egg (fertilization)
Double fertilization of angiosperms (and independently derived in a few gymnosperms)
1 sperm fuses with the egg (fertilization)
1 sperm fuses with the polar nuclei to form the first cell of the endosperm (triploid)

27. Structural barriers to pollination, e.g., pin vs. thrum flowers
bisexual flowers
Structural barriers to pollination, e.g., pin vs. thrum flowers

28. Genetic self-incompatibility, gauged by S-genes
Other mechanisms used by bisexual flowers to avoid self-fertilization:
Genetic self-incompatibility, gauged by S-genes

29. Other mechanisms used by bisexual flowers to avoid self-fertilization:
Genetic self-incompatibility, gauged by S-genes

30. Other mechanisms used by bisexual flowers to avoid self-fertilization:
Genetic self-incompatibility, gauged by S-genes

31. Development of the seed and fruit
The first mitotic division of the zygote is asymmetric
This asymmetry provides the first environmental difference experienced by the differentiating cells and establishes the root-shoot axis
Ovary
Receptacle

32. Development of the seed and fruit
The sporophyte embryo develops from the zygote
The endosperm develops from the triploid endosperm nucleus
Ovary
Receptacle

33. Development of the seed and fruit
The ovule integuments become the seed coat
Tissues of the ovary (and sometimes the receptacle) become the fruit
Ovary
Receptacle

34. Development of the seed and fruit
The ovule integuments become the seed coat
Tissues of the ovary (and sometimes the receptacle) become the fruit

35. Development of the seed and fruit There are many kinds of fruits
Carpels
Flower
Stigma
Stamen
Ovule
Carpel
(fruitlet)
Each
segment
develops
from the
carpel of
one flower
Stigma
Seed
Stamen
Pea
Raspberry
Pineapple
Simple fruit - single carpel of one flower
Aggregate fruit - many separate
carpels of one flower
Multiple fruit - many carpels
of many flowers

36. Development of the seed and fruit
Eudicot embryos develop two cotyledons

37. Development of the seed and fruit
Eudicot embryos develop two cotyledons
Monocot embryos develop a single cotyledon

38. Development of the seed and fruit
Cotyledons may absorb endosperm throughout their functional lives (e.g., castor bean)
Cotyledons may alternatively function as storage organs that absorb the endosperm prior to a seed’s germination (e.g., common bean)

39. Development of the seed and fruit
The radicle is the first structure out of the seed coat
In some eudicots the hypocotyl (embryonic axis below cotyledons) pushes up through the soil

40. Development of the seed and fruit
The radicle is the first structure out of the seed coat
In some eudicots the epicotyl (embryonic axis above cotyledons) pushes up through the soil

41. Development of the seed and fruit
In many monocots, the cotyledon remains in the seed coat, and the coleoptile pushes up through the soil

42. Gymnosperms rely on wind to move pollen from male to female cones
The ovule exudes sap to trap pollen

43. Around 150 m.y.a. some insects fed on both protein-rich pollen of male cones and sugar-rich secretions of female cones…
This may have led evolutionarily to the origin of Angiosperms and animal-mediated pollination

44. Angiosperms have formed many partnerships with animals to move their pollen

45. Questions are welcome