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Seed Plants: Angiosperms. Chapter 23. 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

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outline
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
introduction
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

introduction1
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
phylum magnoliophyta the flowering plants
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
phylum magnoliophyta
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
phylum magnoliophyta1
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
phylum magnoliophyta2
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

phylum magnoliophyta3
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

phylum magnoliophyta4
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
phylum magnoliophyta5
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
phylum magnoliophyta6
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
phylum magnoliophyta7
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
phylum magnoliophyta8
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
phylum magnoliophyta9
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
phylum magnoliophyta10
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
phylum magnoliophyta11
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
phylum magnoliophyta12
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
phylum magnoliophyta13
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
phylum magnoliophyta14
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

phylum magnoliophyta15
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

phylum magnoliophyta16
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

phylum magnoliophyta17
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

phylum magnoliophyta18
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

pollination ecology
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

pollination ecology1
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
pollination ecology2
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
pollination ecology3
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
pollination ecology4
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
pollination ecology5
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

review
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