Flowering Plant Reproduction

1. Flowering Plant Reproduction Chapter 38

2. Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Meiosis occurs in sporangia of sporophytes Sporophyte Meiosis Megasporangium Gametophytes Megaspore Fertilization Fig. 30.10

3. Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Pollen Spores divide by mitosis and develop into mature gametophytes Sporophyte Meiosis Megasporangium Gametophytes Megaspore Embryo sac Fertilization Fig. 30.10

4. Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Pollen Specialized gametophyte cells divide by mitosis to form gametes Sporophyte Meiosis Megasporangium Gametophytes Megaspore Embryo sac Egg 2 sperm Fertilization Fig. 30.10

5. Angiosperms Key Haploid Diploid Microsporangium Alternation of Generations Microspore Meiosis Pollen Gametes fuse during fertilization to produce a zygote Sporophyte Seedling Meiosis Megasporangium Gametophytes Megaspore Embryo Embryo sac Egg Zygote 2 sperm Endosperm Fertilization Fig. 30.10

6. A sporophytes’ male reproductive structures: Stamen Anther Filament Figs. 30.7 & 38.2

7. A sporophytes’ male reproductive structures: Each anther contains multiple pollen sacs (microsporangia) Fig. 38.4

8. A sporophytes’ male reproductive structures: Each pollen sac contains mutiple diploid microsporocytes (microspore mother cells) Fig. 38.4

9. A sporophytes’ male reproductive structures: Each microsporocyte divides by meiosis to produce 4 haploid microspores Fig. 38.4

10. A sporophytes’ male reproductive structures: Each microspore divides once by mitosis to form an immature male gametophyte (pollen grain) Fig. 38.4 A single tube cell encloses a single generative cell

11. 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 Fig. 38.4 The adult male gameto-phyte is a fully mature, indepen-dent plant with only 3 cells

12. A sporophytes’ female reproductive structures: Carpel Stigma Style Ovary Ovule Receptacle Figs. 30.7 & 38.2

13. A sporophytes’ female reproductive structures: Each ovule contains a megasporangium Fig. 38.4 Each megasporangium contains a megasporocyte (megaspore mother cell)

14. A sporophytes’ female reproductive structures: A megasporocyte divides by meiosis to form 4 cells Fig. 38.4 Only 1 of the 4 cells survives: the megaspore

15. A sporophytes’ female reproductive structures: The megaspore’s nucleus divides 3 times: giving 1248 nuclei Fig. 38.4 Membranes then partition the 8-nucleate immature gametophyte cell into 7 smaller cells (one with 2 nuclei)

16. A sporophytes’ female reproductive structures: The 7 cells: 1 egg 1 cell with 2 polar nuclei 5 other cells Fig. 38.4 The 7 cells comprise the mature, completely dependent female gametophyte (embryo sac)

17. 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 Fig. 38.6

18. Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac Fig. 38.6

19. Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac Fig. 38.6

20. Double fertilization of angiosperms (and independently derived in a few gymnosperms) The 2 sperm cells travel down the pollen tube to the embryo sac Fig. 38.6

21. 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) Fig. 38.6

22. In chapter 30 we saw some mechanisms used by plants to avoid self-fertilization; bisexual flowers also use: Structural barriers to pollination, e.g., pin vs. thrum flowers Fig. 38.5

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

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

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

26. 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 Fig. 38.7

27. Development of the seed and fruit The sporophyte embryo develops from the zygote The endosperm develops from the triploid endosperm nucleus Ovary Receptacle Fig. 38.7

28. 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 Fig. 38.7

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

30. 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 Multiple fruit - many carpels of many flowers Aggregate fruit - many separate carpels of one flower Simple fruit - single carpel of one flower Fig. 38.9

31. Development of the seed and fruit Fruits aid seed dispersal The ovary wall becomes either a dry or fleshy fruit

32. Development of the seed and fruit Fruits aid seed dispersal Many dry fruits are wind dispersed

33. Development of the seed and fruit Fruits aid seed dispersal Some dry fruits are animal dispersed

34. Development of the seed and fruit Fruits aid seed dispersal Many fleshy fruits are animal dispersed

35. Development of the seed and fruit Fruits aid seed dispersal Unless the dispersers become extinct!

36. Development of the seed and fruit Fruits aid seed dispersal Some fruits disperse seeds explosively (e.g., some mistletoes)

37. Development of the seed and fruit Fruits aid seed dispersal Some fruits make seeds buoyant, to aid dispersal by water

38. Development of the seed and fruit Eudicot embryos develop two cotyledons Fig. 38.8

39. Development of the seed and fruit Eudicot embryos develop two cotyledons Monocot embryos develop a single cotyledon Fig. 38.8

40. 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) Fig. 38.8

41. 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 Fig. 38.10

42. 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 Fig. 38.10

43. Development of the seed and fruit In many monocots, the cotyledon remains in the seed coat, and the coleoptile pushes up through the soil Fig. 38.10

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

45. 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

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

47. Some of these partnerships are the best known cases of co-evolution: mutual evolutionary influence Figs and fig wasps

48. Some flowers provide nurseries for their pollinators’ offspring Figs and fig wasps

49. Some flowers provide food (e.g., nectar or pollen) to their pollinators Honey bee collecting pollen and nectar

50. Some flowers provide food (e.g., nectar or pollen) to their pollinators Kigelia africana “sausage tree”