Plant Reproduction and Development

1. Plant Reproduction and Development Chapter 27

2. Flowers – Basic Concepts • reproductive structures of angiosperms • monoeciousvs. dioecious • monoecious: each flower has both male and female structures • dioecious: some individuals have “male flowers”, others “female” • multipurpose structures • production of sexual spores and gametes • site of fertilization and embryo, seed, and fruit development • facilitate pollination • transfer of pollen from one plant to another of same species • functions and methods of pollination

3. Various Animal Pollinators

4. Flower Structure • pedicel (peduncle): short stem that attaches flower to plant • receptacle: base of flower from which all other parts emerge • sepals (calyx) • green leaves  produce sugars (photosynthesis)  nourish flower • help protect rest of flower • petals (corolla) • do not photosynthesize • attract pollinators, if colorful and/or elaborate in shape • stamens • male reproductive structures (many) • filament • anther • cells divide by meiosis microsporespollen grains • male gametophytes will produce two sperm cells each • chemical substances to attract pollinators • carpel (pistil) • female reproductive structures (usually one or a few) • stigma • style • ovary:contains one or more ovules • cells in ovules divide by meiosis megasporesembryo sacs • female gametophytes • each contains one egg cell + a few other cells

5. Fig. 27.2 Anatomy of a flower

6. Flower structure

7. nectaries • glands producing sugary “nectar” • diversity among flowers and pollen • pollen is species-specific (why?) • complete vs. incomplete flowers • perfect vs. imperfect flowers Fig. 27.6 Pollen grains from (a) grass, (b) goldenrod, and (c) willow

8. The Formation of Gametes • production of male gametes (sperm) • diploid microsporocytes in anthers of stamens undergo meiosis • forms four haploid microspores each • each microspore then divides by mitosis • this produces a haploid, 2-cell male gametophyte • microgametophyte • pollen grains • pollen grains • each consists of two cells • generative cell • produces twosperm cells • tube cell • forms the pollen tube • encloses the generative cell • surrounded by a tough outer membrane

9. production of female gametes (eggs) • eggs are produced within ovules • ovules are contained within ovary of carpel • integuments • tough layers that surround each ovule • micropyle • single opening through integuments • process • diploid megasporocytes in each ovule undergo meiosis • forms 4 haploid megaspores each • three of these then degenerate • the surviving one divides 3 times by mitosis • produces a haploid, 7-cell female gametophyte • megagametopyte • embryo sac • embryo sacs • each consists of 7 cells • 6 have a single nucleus and are haploid • 1 has 2 nuclei and is diploid • only cell nearest micropylewill become the egg • cell with 2 nuclei is endosperm mother cell • polar nuclei

10. Fig. 27.5 Life cycle of flowering plants

11. Fertilization • pollen from one flower lands on stigma of another flower • must be of same species • stages of fertilization • tube cell of pollen grain forms a pollen tube • pollen tube grows down through carpel • tube penetrates micropyle of an ovule • generative cell of pollen grain divides to form 2 sperm cells • the sperm travel down pollen tube • one fuses with the egg • fertilization forms a diploid zygote • now back to sporophyte (diploid, 2n) stage • 2ndfuses with the 2 polar nuclei of endosperm mother cell • “double fertilization” • forms a triploid (3n) primary endosperm cell

12. Fig. 27.5 Life cycle of flowering plants

13. Close-up of fertilization in flowering plants

14. Fig. 27.5 Life cycle of flowering plants

15. events following fertilization • dramatic transformations in the flower • zygote grows into an embryo • primary endosperm cell develops into endosperm • surrounds and nourishes embryo while in seed • ovule develops into a seed • entire ovary develops into a fruit • remember that each ovule can be fertilized • why most fruits have many seeds Pea flower and pea pod

16. Fruit and Seed Dispersal • necessity and functions of dispersal • reduces competition by separating seeds • scatters seed to new areas and habitats • fruits function to disperse a plant’s seeds • burstingapart, wind, water, animal species Fig. 27.10 Methods of fruit and seed dispersal

17. Other methods of fruit and seed dispersal

18. Asexual Reproduction • some plants produce new individuals this way • most plants produce asexual structures • vegetative reproduction  vegetative structures • diploid structures, always formed through mitosis • examples of vegetative structures • runners (stolons), rhizomes, bulbs, tubers, and “leaf shoots” • parthenocarpy • development of fruits without fertilization • contain no embryos and no seeds (seedless fruits) Fig. 27.12 Example of asexual structure and asexual offspring

19. Fig. 24.19 Different kinds of asexual, vegetative structures. These are all modified stems.