Plant Reproduction

1. Plant Reproduction Chapter 41

2. Flower Initiation

3. Flowering Response to Daylength

4. Plants Can “Remember”

5. Flowering Model

6. Evolution of the Flower • Pollen matures within the anthers and is transported to the stigma of another flower. • When pollen reaches the stigma, it germinates, and a pollen tube grows down, carrying sperm nuclei to the embryo sac. • seed matures within ripening fruit

7. Floral Evolution • Characteristics • A complete flower has four whorls, while an incomplete flower lacks at least one. • calyx, composed of sepals, makes up outermost whorl • petals collectively make up the corolla • stamens collectively compose androecium • stamens made up of filament and anther

8. Floral Evolution • Gynoecium refers to the collection of female parts in a flower. • single or fused carpels also referred to as simple or compound pistils • ovules produced in pistil’s swollen ovary • style - slender neck • stigma – pollen receptive structure

9. Angiosperm Flower

10. Formation of Angiosperm Gametes • Plant sexual life cycles are characterized by an alternation of generations. • Diploid sporophyte gives rise to haploid gametophyte generation. • Male gametophytes (microgametophytes) - Pollen grains • Female gametophyte (megagametophyte) - Embryo sac

11. Pollen Grain and Embryo Sac Formation

12. Fertilization • Double Fertilization results in two key developments: • Fertilization of the egg. • Formation of endosperm. • Pollen grains adhere to the stigma and grow a pollen tube that pierces the style. • Grows until it reaches the ovule in the ovary.

13. Pollen Tube Formation and Fertilization

14. Pollination • Pollination - Pollen is placed on the stigma. • Early seed plants pollinated passively. • Pollination by Animals • Bees - Initially locate food sources by odor, and then orient on a flower by its shape, color, and texture. • May drive coevolution.

15. Pollination • Other Insects • Butterflies • Moths • Birds • Many plants produce large amount of nectar to attract birds. • Hummingbirds • Red colors tend to attract birds, while carotenoids tend to attract insects because they are visible in the UV range.

16. Pollination • Other Animals • Bats • Rodents • Monkeys • Wind-Pollinated Angiosperms • Typically have small, greenish, odorless flowers with reduced or absent corollas. • Often grouped in large numbers and hang down in tassels.

17. Self-Pollination • Two basic reasons for self-pollination. • Ecologically advantageous as they do not need to be visited by animals, and thus do not have to expend energy producing attractants. • Produces more uniform progeny than outcrossing. • Well-adapted to particular habitats.

18. Self-Pollination • Factors Promoting Outcrossing • Dioecious plants produce only ovules or only pollen on a single individual. • Monoecious produce both on same plant. • Dichogamous - Functional stamens and pistils present on same plant, but reach maturity at different times.

19. Self-Pollination • Self-incompatibility results when pollen and stigma recognize each other as genetically related and pollen tube growth is blocked.

20. Asexual Reproduction • Vegetative Reproduction - New plants are cloned from adult parts. • Runners • Rhizomes • Suckers • Adventitious Plantlets • Apomixis - Embryos in seeds produced asexually from the parent plant. • New individuals are genetically identical to parents.

21. Life Span of Plants • Annual Plants • Annual plants grow, flower, and form fruits and seeds within one growing season, and then die when the process is complete. • Grow rapidly under favorable conditions. • Developing flowers or embryos use hormones signaling nutrient reallocation.

22. Life Span of Plants • Biennial Plants • Biennial plants have life cycles that take two years to complete. • Photosynthate stored in underground storage organs during the first year. • Flowering stems are produced during the second year.

23. Life Span of Plants • Perennial Plants • Perennial plants grow year after year. • Majority of vascular plants are perennial. • Food is often stored in roots or underground stems which can become relatively large. • Trees and shrubs generally flower repeatedly. • Deciduous or Evergreen.