Plant Reproduction and Development

1. Chapter 44 Plant Reproduction and Development

2. How do plants reproduce? • Asexually • Existing plant uses mitosis – identical • Lilac bushes that sprout new trunks from the root • Strawberries and runners • Tulips and other bulbs grow new, smaller bulbs • Sexually • Fusion of gametes from parents

3. Alternation of generations • Plant sexual life cycles alternate between two multicellular stages, haploid and diploid

4. Sexual Life Cycle • Sporophyte – multicellular diploid • Garden plants, produce flowers • Produces specialized reproductive cells that undergo meiosis to form haploid spores • Spores undergo mitosis to form multicellular haploid gametophyte • Angiosperms and Gymnosperms produce separate male and female gametophyte stages

5. Sexual Life Cycle of a Flowering Plant Diploid mother cells develop in anthers (male) or ovaries (female) Meiosis produces haploid spores Mitosis of the spores  male & female gametophytes  sperm & egg Pollen carries sperm to flower, sperm travel in tube to female gametophyte Fertilization  diploid zygote Zygote develops into embryo, seedling, mature sporophyte

6. Alternation of Generations mother cell spores MEIOTIC CELL DIVISION flower stigma male gametophyte (pollen grain) anther In the flower, diploid mother cells develop in the reproductive structures: anthers (male) and ovaries (female) 1 Meiotic cell division of mother cells in the sporophyte produces haploid spores 2 Mitotic cell division of the spores forms male gametophytes (pollen), which produce sperm, and female gametophytes, which produce eggs 3 ovule sperm ovary Pollen carries the sperm to the female reproductive structure of a flower; sperm travel within a pollen tube to the female gametophyte 4 A sperm fertilizes an egg within the female gametophyte, producing a diploid zygote 5 mother cell pollen tube MEIOTIC CELL DIVISION ovule sperm nuclei mature sporophyte spores female gametophyte The zygote develops into an embryo, a seedling, and eventually, a new mature sporophyte 6 egg female gametophyte FERTILIZATION seedling seed haploid (n) seed fruit diploid (2n) embryo

7. Sexual Life Cycle Varies between Plants • Size, complexity and lifespan of sporophyte and gametophyte varies • Mosses, liverworts – gametophyte is independent • Resulting sporophyte grows on gametophyte • Ferns – sperm fertilize eggs in independent gametophyte, zygote begins growing on gametophyte but sporophyte develops its own roots and leaves – becomes dominant stage

8. Angiosperms and Gymnosperms • Differ from mosses, liverworts, ferns • Diploid sporophyte is the dominant stage • In angiosperms and gymnosperms, sperm is transported within pollen grain. In mosses, liverwort and fern all require water for fertilization (sperm swim to eggs) • Gametophytes are very, very small

9. Flower Structure • Flower – reproductive structure of angiosperm • Complete flower – has 4 sets of modified leaves • Sepals, petals, stamens, carpels • Petunia, rose, lily

10. Complete Flower Structure • Sepal – at base of flower • In monocots, resemble petals • In dicots – green and leafy • Surround and protect flower bud • Petals – brightly colored, advertise for pollinators • Stamens – attached above petals • Filament with anther, pollen • Carpel – vase shaped, sticky stigma on elongated style, bulbous ovary at base of carpel – one or more ovules where female gametophyte develops • Fertilized ovule becomes seed and dev. into fruit (encloses)

11. A Complete Flower anther petal stamen filament stigma style carpel sepal ovary ovules (a) A representative dicot flower

12. Incomplete Flower Structure • Lack one or more of 4 floral components • Grass (lack petals, sepals) • Also described as imperfect • Produce separate male and female flowers, often on a single plant (zucchini) • American holly, female produces red berries

13. Zucchini Flowers – male and female

14. Animation: Pollen Development

15. Pollen is the Male Gametophyte • Develop within anthers of the sporophyte • Microspore mother cells develop within pollen sacs of the anther • Meiosis produces 4 haploid microspores • Each produces an immature male gametophyte (pollen grain)by mitosis, contains the generative cell • Tube cell + generative cell in the pollen cell • The generative cell undergoes mitosis to form 2 sperm cells.

16. Male Gametophyte Development pollen sacs microspore mother cell anther 1 Microspore mother cells develop within the pollen sacs of the anther of a flower MEIOTIC CELL DIVISION sporophyte microspores 2 Meiotic cell division produces four haploid microspores tube cell nucleus mature pollen grain Immature pollen grain tube cell cytoplasm sperm cells stigma generative cell 4 The generative cell produces two sperm cells by mitotic cell division; the male gametophyte is now mature tube cell nucleus 3 Each microspore produces an immature male gametophyte (a pollen grain) by mitotic cell division haploid (n) diploid (2n)

17. Pollen Tough, waterproof outercoat Characteristic of the plant species Used to identify climate in fossils

18. Wind-Pollinated Flowers Anther, pollen

19. Female Gametophyte Forms in ovule Species vary – one to several dozen ovules Megapore mother cell develops within ovule Meiosis produces 4 haploid megaspores, 3 degenerate Remaining megaspore form 8 nuclei by mitosis (3X mitosis) Plasma membranes form, 7 cells – 3 at one end (1 N each), one is the egg

20. Female Gametophyte Development ovule megaspore mother cell A megaspore mother celldevelops within each ovule of the ovaries of a flower 1 ovary integuments MEIOTIC CELL DIVISION Cytoplasmic division produces the seven cells of the mature female gametophyte 4 Meiotic cell division produces four haploid megaspores; three degenerate 2 megaspores central cell with two nuclei female gametophyte egg cell The single remaining megaspore forms eight nuclei by mitosis 3 haploid (n) diploid (2n)

21. Animation: Ovule Development

22. Pollination and Fertilization • Pollen grain lands on stigma • Absorbs water, breaks out of coat and elongates through stigma • Pollen tube reaches ovule • Double fertilization – both sperm fuse with cells of the female gametophyte • One sperm fertilizes egg  zygote • One sperm fertilizes central cell, mitosis produces endosperm

23. Pollination and Fertilization of a Flower pollen grain 2 A pollen tube grows down through the style of the carpel to the ovary; the tube cell nucleus travels at the tip of the tube, and the two sperm follow close behind tube cell nucleus sperm pollen tube 1 Pollination occurs when a pollen grain lands on the stigma of a carpel sperm tube cell nucleus Double fertilization: 3 One sperm fuses with the central cell ovule central cell ovary One sperm fuses with the egg cell egg

24. Animation: Pollination and Fertilization

25. Fruit and Seed Development Female gametophyte and integuments become seeds Ovary becomes fruit Petals, pollen, stamens dry up and fall off

26. Development of Fruit and Seeds in a Pepper ripening sepal ovary wall “flesh” of pepper ovary pepper fruit ovule seed petal pepper flower pepper fruits

27. Seed Development • Three processes transform ovule into seed • Integuments become seed coat • Triploid central cell divides to form endosperm • Zygote develops into the embryo • As seed matures, embryo differentiates into shoot and root • Shoot includes 1 or 2 cotyledons – absorb food from endosperm • Monocot – most of endosperm stays in seed until germination • Dicot – cotyledons absorb most of the endosperm, so the mature seed is full of embryo

28. Seed Structures • Monocot • Shoot • Coleoptile – sheath that surrounds embryonic leaves • Dicot • Shoot • Hypocotyl • Epicotyl

29. Seed Development integuments (diploid) seed coat central cell (triploid) endosperm zygote (diploid) embryo fertilized ovule seed (a) Early development of the seed seed coat embryonic root endosperm embryonic leaves cotyledon shoot coleoptile hypocotyl shoot embryonic leaves seed coat embryonic root cotyledons (c) Bean seed (dicot) (b) Corn seed (monocot)

30. Animation: Embryo and Endosperm Development

31. Germination • Germination – sprouting of seed • Embryo grows and breaks out of seed • Forms seedling • Warmth and moisture are necessary

32. Dormancy • Some seeds have a period of dormancy • Resist adverse environmental conditions • Dormancy solves 2 problems • Prevents seeds from germinating within moist fruit • Environmental conditions optimal for germination may not coincide with conditions that will allow seedling to survive and mature • Seeds mature in fall – in temperate climate, it isn’t a good time to germinate • In moist, tropical regions dormancy is less common

33. Additional Requirements for Germination • Necessary to break dormancy • Drying – often dispersed by fruit eating animals, excreted and dry our • Cold – prolonged sub freezing temp. – ensures that seeds released in temperate weather do not germinate • Seed coat disruption – weathered or partially digested before germination can occur • Desert plants have seeds that are water soluble

34. Cotyledons Nourish the Developing Plant

35. Germination Embryo absorbs water, seed coat bursts Root emerges first and grows, absorbing water and minerals Shoot cells elongate and push upward Monocots - energy comes from endosperm, digested by cotyledons and transferred to embryo Dicots – cotyledons have already absorbed endosperm so they transfer energy to embryo

36. Germination, part 2 • Seeds are buried in soil and must be protected • Root tip protected by root cap • Monocot – coleoptile encloses shoot tip to protect • Dicot – shoot forms a hook, as grows clears a path for downward pointing apical meristem • Cotyledons are carried out of the soil, become green and photosynthetic, transfer stored and new food to shoot • True leaves take over photosynthesis, cotelydons die back

37. Seed Germination true leaves coleoptile root (a) Corn (monocot) true leaves cotyledon epicotyl cotyledons hypocotyl hook seed coat withered cotyledons hypocotyl root (b) Bean (dicot)

38. Plants and their Pollinators • Coevolution – each as acted as an agent of natural selection on the other • Some flowers provide food • Beetles, moths, butterflies, hummingbirds • Animals distribute pollen • Flower colors have coevolved to match the color vision of the animal • Bees see UV light so flowers are white, blue, yellow, orange • Marking s that point to the center of the flower • Structural adaptations - nectar containing tubes, stamens, smell, etc.

39. UV Patterns Guide Bees to Nectar far- red near UV red orange yellow green blue violet human bee 700 600 500 400 wavelength (nm) (a ) A comparison of color vision in humans and bees human vision bee vision (b ) Flower color patterns seen by humans and bees

40. “Pollinating” a Pollinator

41. Vertebrate Pollinators Hummingbirds need a lot of energy so the flowers they pollinate produce more nectar than flowers that are pollinated by insects.

42. Mating Decoys Particularly orchids Mimic female wasps, bees or flies in smell and shape. Males attempt to copulate but only pick up pollen packet which transfers to the next flower

43. Nurseries for Pollinators • Some insects pollinate the flower, then lay their eggs in the flower’s ovary • Milkweed and milkweed bugs • Yucca and yucca moth • Visit – collect – visit and drill hole, lay eggs – pollinate stigma with pollen • Neither can reproduce without the other

44. Fruit helps disperse seeds Disperse seeds far away so there is no competition Adult plants can withstand more damage than seedlings Species will be more successful if they disperse their seeds a distance Many different types of dispersal Seed dispersion methods

45. Water-Dispersed Fruit

46. Wind-Dispersed Fruits

47. Clingy Fruits

48. Colored fruit attracts animals • Blackberries, raspberries, strawberries, tomatoes, peppers - small seeds that animals swallow • Eventually excreted unharmed • Some seed coats must be scraped or weakened by an animal’s digestive tract before germination • Transported away from its parent plant and ends up with is own fertilizer! • Seed dispersal video