Chapter 31 Plant Reproduction

1. Chapter 31 Plant Reproduction

2. Think Sporophyte and Gametophyte • Plants reproduce sexually, often relying on pollinators to bring sperm and egg together. • The sporophyte (diploid) develops from the zygote by mitosis; it consists of roots, stems, leaves, and flowers • Meiosis of cells within flowers produces the small haploid gametophytes, which in turn produce either sperm or eggs.

3. Alternation of Generations

4. Component of Flowers • The specialized parts of the flower grow from the modified end of the floral shoot – the receptacle. • Sepals: (collectively called the calyx) are the outermost green, leaflike parts. • Petals (collectively called the corolla) are the colored parts of located between the reproductive structures and the sepals.

5. Continue… • Flowers differ from the other tissues of the plant in their fragrance and colors (Carotenoids and anthocyanins), which are attractive to pollinators.

7. Where Pollen and Eggs Develop • Male parts – called stamens are located inside the corolla • Stamen consist of a slender stalk (filament) capped with an anther • Inside the anthers are pollen sacs in which pollen grains develop • Look at the previous picture to see the male parts in a diagram

8. Continue… • Female parts are located in the central part of the flower • Carpel is the vessel-shaped structure with an expanded lower chamber (ovary), slender column (style) and upper surface (stigma) for pollen landing. • In ovary eggs develop, fertilization occurs and seeds mature. • Refer to diagram

9. Continue… • Perfect flowers have both male and female parts (may or may not be on the same plant) • Imperfect flowers is missing one of the sex

10. From Microspores to Pollen Grains • In anthers, each diploid “mother” cell divides by meiosis to form four haploid microspores. • Each microspores will divide to form pollen grains • One cell in each pollen grain will produce the sperm; the other will form the pollen tube

11. From Megaspores to Eggs • In carpel, a mass of tissue forms an ovule (potential seed) enclosed by integuments. • A diploid “mother” cells divides by meiosis to produce haploid megaspores, one of which will undergo mitosis three times to produce a cell with eight nuclei • The nuclei migrate resulting in an embryo sac (female gametophyte) with seven cells; one cell has two nuclei and will become the endoperm (nutrition for embryo); another cell will be the egg

12. From Pollination to Fertilization • Pollination is the transfer of pollen to the surface of the stigma by the actions of insects, birds, or other agents. • In germination, a pollen tube forms producing a path that the two sperm will follow to the ovule.

13. Continue… • When the pollen tube reaches an ovule, it penetrates the embryo sac, and the two sperm are released. • One sperm fuses with the egg nucleus to form a diploid zygote • The other sperm nucleus fuses with the two endoperm nuclei to yield a triploid “Primary endosperm cell” that will nourish the young sporophyte seedling.

15. Pollen Grain

18. Formation of the Embryo Sporophyte • The zygote undergoes repeated divisions to form an embryo sporophyte as a part of an ovule and is accompanied by formation of fruit. • Cotyledons (seed leaves) develop for the purpose of utilizing the endosperms during germination.

20. Seed Formation • From zygote to embyro, the plant supplies nutrition until the time when the connection between the ovule and ovary wall is broken • The mature ovule integuments thicken inot seed coats around the seed (a mature ovule containing embryo and food reserve)

21. Continue… • Embryo is inactive • Seed dehydrates (5 -15% water) • Embryo surrounded by endosperm, enlarged cotyledons or both

22. Fruit Formation • A fruit mature ovary with seeds (ovules) inside; they may be classified as simple aggregate, multiple or accessory. • The pericarp of a fruit consists collectively of endocarp (around the seed), mesocarp (fleshy portion), and exocarp (the skin)

23. Continue… • Immature fruit protects the seed (green, bitter, sour, etc.) • Mature fruit aids in dispersal (colorful and tasty) • Forms from ovary • Does not provide nutrient for seeds

24. Dispersal of Fruits and Seeds • Seeds have coevolved with particular dispersing agents – currents of air or water, or animals passing by • Example: Pericarp of maple seeds extends out like wings to catch the wing and be transported • Some fruits are dispersed by sticking on animal bodies or by passing through the digestive tract to be deposited in the feces • Humans are perhaps the grand dispersing agents by virtue of the long distances to which they carry seeds

25. Seed Germination • Seed frequently undergo a period of dormancy. WHY??? • Requires water, oxygen, and warm temperatures • Root emerges first. WHY AGAIN?

28. Asexual Reproduction of Flowering Plants • Vegetative growth modes includes: runners, rhizomes, corms, tubers, and bulbs. • Parthenogenesis, embryo development from an unfertilized egg, can produce new orange plants.

29. Induced Propagation • Vegetative propagation (“Cuttings”) can result in new plants produced from leaves that form roots. • Tissue Culture propagation can result in whole plants produced from a group of cells.

30. THE END!!