Seed Plants: Angiosperms

1. Seed Plants: Angiosperms Chapter 23

2. Outline • Introduction • Phylum Magnoliophyta – The Flowering Plants • Development of Gametophytes • Pollination • Fertilization and Development of the Seed • Apomixis and Parthenocarpy • Trends of Specialization and Classification in Flowering Plants • Pollination Ecology

3. Introduction • Angiosperms = flowering plants • Seeds enclosed in carpel – resembles folded over leaf and fused at margins • Pistil composed of single carpel, or >2 united carpels • Seed develops from ovule within carpel • Ovary becomes fruit Bleeding hearts

4. Introduction • Angiosperms = Phylum Magnoliophyta • Divided into 2 large classes: • Magnoliopsida - Dicots • DNA and cladistic evidence suggest2groups of dicots should be recognized • Liliopsida - Monocots • Flower = modified stem bearing modified leaves • Most primitive flower • Long receptacle • Many spirally arranged flower parts that are separate and not differentiated into sepals and petals (= tepals) • Flattened and numerous stamens and carpels

5. Phylum Magnoliophyta – The Flowering Plants • Heterosporous • Sporophytesdominant • Female gametophytes wholly enclosed within sporophyte tissue and reduced to only few cells • Male gametophytes consist of germinated pollen grain with 3 nuclei

6. Phylum Magnoliophyta • Development of gametophytes - Female: • 2nmegasporocyte differentiates in ovule • Undergoes meiosis and produces 4 1nmegaspores • 3 degenerate • Remaining cell enlarges and nucleus divides to produce 8 nuclei (without walls) • Outer 2 layers of ovule differentiate into integuments that later become seed coat • Micropyle at one end of ovule

7. Phylum Magnoliophyta • Development of gametophytes – Female cont’d.: • 8 nuclei form 2 groups, 4 near each end of cell • 1 nucleus from each group migrates to cell middle and form central cell • Cell walls form around remaining 6 nuclei • Egg and 2 synergids closest to micropyle • 3 antipodals at opposite end • Female gametophyte = megagametophyte or embryo sac

8. Phylum Magnoliophyta • Development of gametophytes - Male: • Formation of male gametophytes takes place in anthers • 4 patches, corresponding to pollen sacs, of microsporocyte cells differentiate in anther • Each microsporocyte undergoes meiosis to produce 4 1nmicrospores Anther with microspores

9. Phylum Magnoliophyta • Development of gametophytes – Male cont’d.: • Microspores undergo 3 changes: • Divide once by mitosis to form small generative cellinside larger tube cell • Nucleus of tube cell = vegetative nucleus • Members of each quartet of microspores separate • Wall becomes 2-layered • Outer layer (= exine)finely sculptured and contains chemicals that react with chemicals in stigma • Generative nucleus divide to produce 2 sperm Pollen grain

10. Phylum Magnoliophyta • Pollination: • Pollination - transfer of pollen grains from anther to stigma • Self-pollination - pollen grains germinate on stigma of same flower • Fertilization - union of sperm and egg • Pollination by insects, wind, water, animals or gravity

11. Phylum Magnoliophyta • Fertilization and development of the seed: • After pollination, further development of male gametophyte may not take place unless pollen grain: • From different plant of same species • From variety different from that of receiving flower • Pollen tube grows between cells of stigma and style until reaches ovule micropyle • Vegetative nucleus stays at tips of pollen tube, while generative cell lags behind and divides into 2 sperm • Pollen tube enters female gametophyte, destroying synergid in process, and discharges sperms

12. Phylum Magnoliophyta • Fertilization and development of the seed cont’d.: • Mature male gametophyte = germinated pollen grain with vegetative nucleus and 2 sperms within tube cell

13. Phylum Magnoliophyta • Fertilization and development of the seed cont’d.: • Double fertilization: • 1 sperm unites with egg, forming zygote, then embryo • Other sperm unites with central cell nuclei, producing 3nendosperm nucleus developing into endosperm tissue • Endosperm tissue = nutritive tissue for embryo

14. Phylum Magnoliophyta • Fertilization and development of the seed cont’d.: • Endosperm becomes extensive part of seed in some monocots (i.e., corn and other grasses) • Endosperm absorbed into cotyledons in most dicots • Ovule becomes seed, ovary matures into fruit, integuments harden into seed coat

15. Phylum Magnoliophyta • Fertilization and development of the seed cont’d.: • Other types of (female) gametophyte development: • Female gametophyte can have from 4 to 16 nuclei or cells at maturity • Endosperm may be 5x, 9x or 15x

16. Phylum Magnoliophyta • Apomixis and parthenocarpy: • Apomixis -without fusion of gametes but with normal structures otherwise being involved • Embryo from 2nnutritive cell or other 2ncell of ovule, instead of from zygote • Results invegetativelypropagated plant • Parthenocarpy -fruits develop from ovaries with unfertilized eggs. • Results in seedless fruits • Navel oranges and bananas

17. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants: • 1sthistorical classifications for convenience • Modern botanists group plants according to natural relationships based on evolution • Fossil record suggests flowering plants 1stappeared about 160mya during late Jurassic • Flowering plants developed during Cretaceous and Cenozoic • Dominant plants today

18. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • 1stpistil from leaflike structure with ovules along margins = carpel • Edges of blade rolled inward and fused together • Separate carpels of primitive flowers fused together to form compound pistil consisting of several carpels

19. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Inferior ovary (epigynous flower) -receptacle or other flower parts fused to ovary and grown up around it • Superior ovary (hypogynous flower) -ovary produced on top of receptacle • Perigynousflowers -flower parts attached to corolla tube of fused petals, creating floral tube not attached to ovary

20. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Complete flower -has calyx, corolla, stamens and pistil • Incomplete flower -corolla or other flower parts missing • Perfect flower -both stamens and pistil present Male flower Female flower with inferior ovary

21. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Imperfect flower -either stamens or pistil missing • Monoecious species -male and female imperfect flowers on same plant • Dioecious species -plant bears only male flowers and other plants bear only female flowers Male flower Female flower with inferior ovary

22. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Primitive flowering plants • Simple leaves • Flower with numerous, spirally arranged parts, not fused to each other • Flowers radially symmetrical = regular. • Flowers complete and perfect • Superior ovary (hypogynous flower) Magnolia

23. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Specialized flowering plants: • Flower parts fewer and definite in # • Spiral arrangements compressed to whorls • Bilaterally symmetrical flowers = irregular Orchid

24. Phylum Magnoliophyta • Trends of specialization and classification in flowering plants cont’d.: • Specialized flowering plants cont’d.: • Reduction and fusion of parts • Incomplete or imperfect flowers • Inferior ovary Orchid

25. Pollination Ecology • Pollinators co-evolved with plants • 20,000 bee species among current-day pollinators • Bee-pollinated flowers: • Generally brightly colored, mostly blue or yellow • Often have lines or distinctive markings, may function as guides to lead bees to nectar • Bees see UV light (humans do not) In ordinary light In UV light

26. Pollination Ecology • Beetle-pollinated flowers: • Strong, yeasty, spicy or fruity odor • White or dull in color • Some do not secrete nectar, but furnish pollen or food on petals in special storage cells • Fly-pollinated flowers: • Smell like rotten meat • Dull red or brown

27. Pollination Ecology • Butterfly- and moth-pollinated flowers: • Often have sweet fragrances • White or yellow for night-flying moths • Sometimes red, often blue, yellow or orange for butterflies • Nectaries at bases of corolla tubes or spurs for long tongues

28. Pollination Ecology • Bird-pollinated flowers (hummingbirds and sunbirds): • Often bright red or yellow • Little if any odor - Birds don’t have keen sense of smell • Large and part of sturdy inflorescence • Copious amounts of nectar - Birds highly active • Long floral tubes

29. Pollination Ecology • Bat-pollinated flowers: • Primarily in tropics • Open at night when bats foraging • Dull in color • Large enough for bat to insert head or consist of ball-like inflorescence containing large numbers of small flowers

30. Pollination Ecology • Orchid flowers: • Have pollinators among all types mentioned • Some adaptations between orchid flowers and pollinators extraordinary. • Pollen grains produced in little sacs called pollinia (singular: pollinium) with sticky pads at base Ophrys

31. Review • Introduction • Phylum Magnoliophyta – The Flowering Plants • Development of Gametophytes • Pollination • Fertilization and Development of the Seed • Apomixis and Parthenocarpy • Trends of Specialization and Classification in Flowering Plants • Pollination Ecology