Angiosperms II - PowerPoint PPT Presentation

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Angiosperms II

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  1. Angiosperms II Fruits, Seeds, and Embryos

  2. FRUITS • A “fruit” is derived from the ripened ovary (ovaries) and sometimes other associated floral parts • to end the debate then, a tomato is a fruit since it is derived from a flower • The fruit (usually a ripened ovary) is surrounded by the fruit wall or pericarp • This wall is composed of three layers (exocarp, mesocarp, and endocarp) • These layers may be distinct or fused

  3. Endocarp Mesocarp Exocarp Fruit Structures (Pericarp)

  4. Fruit Types For an interactive key to FRUIT TYPES, go to • Multiple Fruits • derived from MANY flowers • pineapple, mulberry

  5. Fruit Types (cont.) • Aggregate Fruits • derived from SEVERAL separate carpels (pistils) of ONE flower • strawberry, raspberry, blackberry

  6. Fruit Types (cont.) • Simple Fruits • derived from ONE carpel or pistil of ONE flower • are either fleshy or dry at maturity

  7. Simple Fruits • Fleshy Fruits (a few types) • with a fleshy hypanthium and/or receptacle = pome (apple) • a single seed with stony endocarp = drupe (plum, peach) • many seeded, endocarp fleshy = berry (grape, tomato) orpepo (pumpkin, watermelon) • Outer layer with a separable rind = hesperidium (orange, lemon, grapefruit)

  8. BERRY DRUPE Fleshy Simple Fruits

  9. PEPO HESPERIDIUM POME Fleshy Simple Fruits (cont.)

  10. Simple Fruits (cont.) • DRY FRUITS • Dehiscent Types • seeds released through one seam = FOLLICLE • seeds released through 2 seams = LEGUME • seeds released though pores or multiple seams = CAPSULE • Indehiscent Types • pericarp hard and thick with a basal cup = NUT • Pericarp soft and thin, no cup = ACHENE, CARYOPSIS etc...

  11. CAPSULE LEGUME FOLLICLE Dehiscent Dry Fruits

  12. NUTS ACHENE Indehiscent Dry Fruits

  13. Why the variation in fruit types? • Fruits are units of dispersal for the seeds • Certain fruits are adapted for dispersal by wind (small, light, winged)

  14. Fruit Dispersal (cont.) • Others are dispersed by animals (fleshy, colored, sweet, or high in energy like nuts; or with spines, hooks) Bidens – tickseed fuits

  15. Fruit Dispersal (cont.) • Some for water dispersal (coconut)

  16. Seeds • A seed is surrounded by the seed coat derived from the integuments • The embryo may have large cotyledons (as in lima beans) and little endosperm • Some seeds have lots of endosperm and thin cotyledons (castor beans)

  17. Pinto Bean vs.Castor Bean

  18. The Grass Seed (Fruit) • Outer pericarp is fused to the seed coat • Single massive cotyledon is called the scutellum • Protective sheaths cover the early shoot (coleoptile) and the root (coleorhiza) • Endosperm is surrounded by a special layer of cells called the aleurone layer

  19. CORN GRAIN coleoptile endosperm coleorhiza scutellum embryonic leaves

  20. Seed Germination • Normal germination requires proper temperature, water, oxygen and sometimes light • If, given proper conditions, a seed does not germinate, we say it is DORMANT • Dormancy is annoying to us, but it is evolutionarily adaptive for the plant

  21. Reasons for Seed Dormancy • Seed coat impervious to water and/or oxygen (imbibition of water is often the first step in germination) • scarification required (physical or chemical) to allow entry of water and/or oxygen • many commercial applications for seed production

  22. Seed Scarification

  23. SeedDormancy • Seed has an immature embryo • Seed has chemical inhibitors in the seed coat that must be leached out

  24. Desert in Bloom

  25. Seed Longevity • Seeds may be dormant for only a few weeks to thousands of years • record is over 10,000 years for Arctic lupine seeds from lemming burrows

  26. Seed Longevity (cont.) • Lotus seeds have been germinated after storage for more than 2,000 years

  27. Seed Banks • Seed Banks help protect angiosperm genetic diversity around the world Kew Gardens, England. Home of the Millennium Seed Bank Project

  28. Embryology • Early embryo development in plants progresses through specific stages: • much of the work done on Capsellabursa-pastoris (“shepherd’s purse”)

  29. CapsellaEmbryology • “ball” stage with basal cell, suspensor and the embryo proper

  30. CapsellaEmbryology (cont.) • “heart-shaped” stage where the embryo’s two cotyledons become obvious and the differentiation of tissues become evident

  31. CapsellaEmbryology (cont.) • “bendingcotyledons” stage where the embryo moves toward its final form

  32. CapsellaEmbryology (cont.) • “Mature embryo” stage

  33. Embryonic Tissue Layers • Thee distinct tissue layers differentiate early in embryo development: • PROTODERM which will give rise to the plant’s epidermis and all associate structures (guard cells, trichomes, epidermal cells) • PROCAMBIUM which will become the primary xylem andphloem tissues (vascular tissues)

  34. Embryonic Tissue Layers (cont.) • GROUND MERISTEM from which will be derived the pith, cortex, and associated structures in the stem and root • These tissue layers correspond in a way to early tissues in animal embryos, namely, the ectoderm, endoderm, and mesoderm • Development of most plant embryos has not been investigated