Ch. 38: Plant Reproduction and Biotechnology

1. Ch. 38: Plant Reproduction and Biotechnology

2. Review: Alternation of generations in moss Gametophyte (n): Produces gametes which fertilize to form a sporophyte Sporophyte (2n): produces haploid spores which divide by mitosis to form plants called gametophytes.

3. Sexual Reproduction in plants: • A. Alternation of generations in angiosperms:

4. Flowers are specialized shoots bearing • reproductive organs of the angiosperm • sporophyte. 1.Stamen = male Carpel = female 2.Pollen grain = sperm producing male gameto- phytes 3.Embryo sac = egg producing female gameto- phytes

5. Complete flowers: all four organs • (sepal, petals, stamen, and carpel) • 5.Incomplete flowers: loacking one or more • of the floral parts (ex. Grasses lack petals) • Bisexual flower: possesses both stamen • and carpel. • Unisexual flower: possesses one one • sexual part • -Monoecious: stamen and carpel are on • the same plant but on different flowers. • -Dioecious: stamen and carpel are found • on different plants.

6. Sagittaria: Dioecious Corn: Monoecious

7. Development of the male gametophyte: • Microsporocyte (in pollen sac of anther) • undergoes meiosis, forming • four haploid cells called • microspores. • Microspores divide once by • mitosis and produces two • cells, one a generative cell, • the other a tube cell. • Generative  Sperm • Tube cell  enclose the • generative cell and • produce the pollen tube • (for sperm delivery)

8. The two-celled structure • is enclosed in a thick • wall that has an • elaborate pattern. • Pollen grain • Pollen becomes a mature male gametophyte when the generative cell divides to form two sperm.

9. Development of female gametophyte: 1.Megasporocyte divides by meiosis to form four haploid cells. 2.Only 1 survives to form the megaspore. 3.Megaspore undergoes mitosis 3 times, forming one large cell with 8 haploid nuclei. 4.The 8 haploid cells are enclosed in the embryo sac. 5.The 8 haploid cells become 4 types of cells: Antipodal, polar, egg, and synergids.

10. -Antipodal: unknown function -Synergids: flank the egg cell and assist in attracting and guiding the pollen tube. -Polar: in cytoplasm; fuses with sperm to form endosperm -Egg: fuses with sperm

11. Plants can prevent self-fertilization by: • 1.Dioecious plants • 2.Bisexual plants can have carpel and stamen • maturing at different times • 3.Self-incompatibility: plant rejects its own • pollen and the pollen of closely related • plants. If a pollen contains an S1 allele that matches the S1 allele in the stigma, the pollen grain will not form a pollen tube  No fertilization.

12. S genes code for a receptor protein (R) in the ECM of the stigma. Another product of the S genes are protein kinases (K) embedded in the plasma membrane. Similar or same S genes  self-incompatibility

13. Double fertilization gives rise to the zygote • and endosperm. Double fertilization = 1.One sperm fuses with egg (2n) 2.Another sperm fuses with polar cells to form the endosperm (3n)

14. After fertilization, the ovule develops into a • seed and the ovary develops into a fruit • enclosing the seed(s). • Endosperm develops from the triploid • nucleus, forming a milky liquid mass. The • endosperm provides nutrients for the • developing embryo and germinating seed. • Embryo development: • -Transverse split: Terminal and basal •  Terminal becomes most of the embryo •  See p. 791, fig. 38.10 for details

15. Structure of the mature seed: • Seed coat: protective • Hypocotyl: point • where cotyledons • attach. • Radicle: where the • hypocotyl terminates; • the embryonic root. • Epicotyl: shoot tip • Monocots: Single cotyledon called scutellum Coleorhiza: covers young root Coleoptile: covers young shoot

16. Ovary develops into fruit: • Fruit: protects the seeds and aids in their • dispersal by wind or animals. • Pollination triggers hormonal changes that • causes the ovary to begin its transformation • into a fruit. •  no pollination, no fruit •  Exceptions: Parthenocarpy (seedless) • Pericarp: thickening wall of the fruit

17. Evolutionary adaptations of seed germination • contribute to seedling survival. • Seeds mature and then enter dormancy; • low metabolic rate and suspension of growth • and development. •  Seeds germinate when conditions are • favorable. • Seed dormancy increases the chances of seedling survival by germinating only when conditions are favorable. • Favorable cues = water, light, animal’s digestive tract

18. Germination from seed to seedling depends • on “imbibition,” the uptake of water. •  Imbibing causes the seed to expand and • rupture its coat and also triggers • metabolic changes in the embryo that • enable it to resume growth. • Enzymes begin digesting the storage • materials in the endosperm and cotyledons • and transfer the nutrients to the embryo. • First to emerge from seed is the radicle. • Next, the shoot. • The hypocotyl, stimulated by light, • straightens, raising the cotyledons and • epicotyl.

19. -Imbibing causes GA (Gibberellins) to be released. -Enzymes from aleurone are released. -Enzymes hydrolyze the food storage for embryo. -Light must be available for leaves to green and plant to develop.

21. Asexual Reproduction in plants: • A. Cloning: “vegetative reproduction” • -Meristematic tissue = undifferentiated cells • -Parenchyma cells can divide and • differentiate into specialized cells • -Fragmentation: tissue from parent plant • can develop into a new plant • -Apomixis: Formation of seeds without • flowers being fertilized. A diploid cell within • the ovule matures into seeds. • Some plants can reproduce both asexually • and sexually. • 1.Advantage of sexual: variety for success, • seed dispersal and seed dormancy • 2.Advantage of asexual: clone rapidly, • offspring are mature fragments, not frail.

22. Vegetative propagation is used extensively • in crop, orchard, and ornamental plant • farming. •  Cutting of shoots/stems •  Grafting: stock is the plant that provides • root system; scion is the twig that is • grafted in.

23. Plant Biotechnology in use of plants and their • products and how humans have altered plants • to suit their purposes. • History: Neolithic (stone age) humans • artificially selected for the best corn (maize). • Pig farmers feed pigs with opaque-2 maize, • a type of corn that is more nutritious.

24. Transgenic plants: Plants that contain genes • from a plant of a different species. • 1.Disease resistant genes • 2.Pest resistant genes • Plant biotechnology has caused great public • debate: • 1.Unknown health risks associated with • genetically modified foods. • 2.Possible damage to other organisms that • rely on foods not previously modified. • 3.Potential for a genetically modified crop • to hybridize with a weed, producing a • “superweed.”