Plants and Pollinators by chenshu

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									Plant Reproduction
and Development
      Biology 1030
  Principles of Biology


                          1
   Flower                    STAMEN                        CARPEL
                      (male reproductive part)     (female reproductive part)
  Structure              filament   anther         stigma     style       ovary


• Nonfertile parts
   – Sepals
   – Receptacle
• Fertile parts
                                                                      OVULE
                       petal (all petals
   – Male stamens      combined are the
                                                                      (forms
                                                                      within
                       flower’s corolla)                              ovary)
   – Female carpels
     (ovary)           sepal (all sepals
                       combined are the
                       flower’s calyx)
                                                 receptacle
                                                                      2
 Angiosperm
 Life Cycles
                                        CHERRY TREE
                                                                 CHERRY
•Dominant form is                             mature
                                                                BLOSSOM

                                            sporophyte
the diploid sporophyte           seed


                                              DIPLOID      meiosis       meiosis
                            fertilization
•In flowers, haploid                          HAPLOID
                                                             in
                                                           anther
                                                                           in
                                                                          ovary

spores formed by               gametes
                               (sperm)                    microspores
meiosis develop into                 (mitosis)
                                                male
                         gametes (eggs) gametophyte
gametophytes                                                         megaspores

                           (mitosis)          female
                                            gametophyte
                                                                          3
          Kinds of Flowers
• Perfect flowers
  – Have both male and female parts
• Imperfect flowers
  – Are either male or female
  – Same plant may have both male and
    female flowers
  – Sexes may be on separate plants
                                        4
       Plants and Pollinators
• Pollen:
  – Sperm packed inside a nutritious package
  – Transferred first by wind currents
  – Later transferred by insects
• Plants that attracted insect pollinators
  with flowers had a reproductive
  advantage

                                               5
         Pollen Formation
• Each anther has four pollen sacs
• Inside the pollen sacs, cells undergo
  meiosis and cytoplasmic division to form
  microspores
• Microspores undergo mitosis to form
  pollen grains

                                             6
          Egg Formation - 1

• Ovules form inside the ovary of a flower

• Protective integuments form around the ovule

• Inside, cells divide by meiosis to form haploid

  megaspores

• All megaspores but one disintegrate

                                                    7
          Egg Formation - 2
• Remaining megaspore undergoes mitosis
  three times without cytoplasmic division
• Result is a cell with eight nuclei
• Cell division produces seven-cell
  gametophyte
• One cell has two nuclei and will become the
  endosperm, another is the egg
                                                8
                Pollination

• Transfer of pollen grains to a receptive stigma

• Pollen can be transferred by a variety of

  agents

• When a pollen grain lands on the stigma it

  germinates

                                                9
         Double Fertilization
• A pollen tube grows down through the ovary
  tissue
• It carries two sperm nuclei
• When pollen tube reaches an ovule, it
  penetrates embryo sac and deposits two
  sperm
• One fertilizes the egg, other fuses with both
  nuclei of endosperm mother cell
                                                  10
      Endosperm Formation
• Occurs only in angiosperms
• Fusion of a sperm nucleus with the two nuclei
  of the endosperm mother cell produces a
  triploid (3n) cell
• This cell will give rise to the endosperm, the
  nutritive tissue of the seed


                                                   11
   Seeds and Fruits
                      ovule

                      wall of
                      ovary




• The seed is the mature ovule
• The fruit is the mature ovary



                                  12
      Structure of a Seed
• Protective seed coat is derived from
  integuments that enclosed the ovule
• Nutritious endosperm is food reserve
• Embryo has one or two cotyledons
  – Monocot has one
  – Eudicot has two

                                         13
           Seed Formation
• Fertilization of the egg produces a diploid
  sporophyte zygote
• The zygote undergoes mitotic divisions to
  become an embryo sporophyte
• Seed: A mature ovule, which encases an
  embryo sporophyte and food reserves
  inside a protective coat
                                           14
     Nourishing the Embryo
• Eudicot embryo
  – Absorbs nutrients from endosperm
  – Stores them in its two cotyledons
• Monocot embryo
  – Digestive enzymes are stockpiled in the
    single cotyledon
  – Enzymes do not tap into the endosperm
    until the seed germinates
                                              15
       Fruit: A Mature Ovary
• Simple fruit
  – Derived from ovary of one flower
• Aggregate fruit
  – Derived from many ovaries of one flower
• Multiple fruit
  – Derived from ovaries of many flowers
• Accessory fruit
  – Most tissues are not derived from ovary
                                              16
         Aggregate Fruits
• Formed from the many carpels of a
 single flower
• Made up of many simple fruits attached
 to a fleshy receptacle
• Blackberries and raspberries are
 examples
                                       17
     Multiple Fruits
• Formed from individual
  ovaries of many flowers that
  grew clumped together
• Examples:
  – Pineapple
  – Fig

                                 18
               Accessory Fruits

               Apple              Strawberry


                             receptacle


ovary tissue


seed

                                       ovary
enlarged
receptacle

                                               19
              Seed Dispersal
• Fruit structure is adapted to mode of dispersal
• Some modes of seed dispersal:
  – Wind currents
  – Water currents
  – Animals




                                                20
       Asexual Reproduction
• New roots or shoots grow from
  extensions or fragments of existing plants

• Proceeds by way of mitosis

• All offspring are genetically identical
  (unless mutation occurs)

                                            21
           Natural Clones
• Forest of quaking aspen in Utah
  – 47,000 trees are genetically identical
    shoots
  – Roots are all interconnected
• Oldest known clone
  – Ring of creosote bushes in Mojave desert
   that is 11,700 years old
                                               22
       Artificial Propagation
• New plant develops from cuttings or
  fragments of shoot systems
  – African violets and jade plants can be
    propagated from leaf cuttings
• Tissue-culture propagation
  – Tiny plant bits are grown in rotating flasks
    containing a liquid growth medium
                                                   23
         Seed Germination
• Process by which the plant embryo
 resumes growth after seed dispersal
• Depends upon environmental factors
  – Temperature
  – Soil moisture
  – Oxygen levels

                                       24
     Splitting the Seed Coat
• Water molecules move
  into a seed
• As water moves in, the
  seed swells and the
  coat ruptures


                               25
  Growth of a Corn Plant
                              coleoptile



                                       first
                                       foliage                 prop
               branch                  leaf               roots that
                                                            form on
               root                                             corn
primary root
                                                          seedlings
                                                            and that
                                                              afford
                                           adventitious   additional
                                           root             support
                         primary                             for the
                         root                                rapidly
                                     branch root            growing
                                                               stem
                                    primary root
germinating
   seed        new seedling



                                                                       26
 Growth of a Bean Plant


             primary leaf



  hypocotyl




two                         primary   branch
cotyledons                  root      root


                                               27
 Genes Govern Development
• All cells in a plant inherit the same
  genes
• Positional differences and unequal
  cytoplasmic divisions lead to differences
  in metabolic output
• Activities of daughter cells begin to vary
  as a result of selective gene expression
                                           28
 Hormones and Development
• Genes governing the synthesis of
  hormones are activated in some cells
  but not others
• This can start different cell lineages
  down different developmental pathways
• Hormones interact with other gene
  products and with the environment to
  affect growth and development

                                       29
Plant Hormones
 •   Gibberellins
 •   Auxins
 •   Cytokinins
 •   Ethylene
 •   Abscisic Acid



                     30
               Gibberellins
• More than 80 forms have been isolated
  from plants, as well as from fungi
• In nature, gibberellins:
  – Help seeds and buds break dormancy
  – Make stems lengthen
  – Influence flowering
• Applied by growers to enhance stem
  length, control ripening                31
                Auxins
• Promote stem lengthening
• Play a role in responses to gravity and
  light
• Indoleacetic acid (IAA) is the most
  common auxin in nature
• Certain synthetic auxins are used as
  herbicides
                                            32
       Auxin Experiment

                                                        control
           cut tip of   uncut      tip on
           coleoptile   control     agar
oat seed




                                                                   33
           Result: agar with diffused auxins enables cell lengthening
               Cytokinins
• Promote cell division
• Most abundant in root and shoot
  meristems and in maturing fruits
• In mature plants, produced in roots and
  transported to shoots
• Used to artificially extend the shelf life of
  cut flowers; delays leaf death
                                             34
          Ethylene

• Induces aging responses

• Unlike other plant hormones,

 ethylene is a gas

• Used to ripen fruits for market

                                    35
       Abscisic Acid (ABA)

• Causes the suspension of growth;
 promotes dormancy of buds and seeds

• Used to induce dormancy in plants to be
 shipped

• Also plays a role in drought response
                                          36
        Herbicides
• Kill weeds by disrupting their
  metabolism and growth
• Frequent contaminant of many
  ecosystems




                                   37
           Plant Tropisms
• Adjustment of plant growth toward or
 away from an environmental stimulus

• Phototropism - stimulus is light
• Gravitropism - stimulus is gravity
• Thigmotropism - stimulus is contact with
  an object

                                         38
            Phototropism
• Change in growth in response to light
• Controlled by the flow of auxin produced
  in the plant tip




                                        39
             Gravitropism

• Roots tend to grow toward pull of
  gravity; shoots grow against it
• Gravitational field is sensed via position
  of statoliths (a type of amyloplast)
• Auxin is involved in response; causes
  asymmetric cell elongation
                                           40
            Thigmotropism
• Growth in response to contact with a solid
  object
• Allows vines and tendrils to wrap around
  supports
• Cells on contact side elongate, causing stem
  to curl
• Auxin and ethylene may be involved

                                                 41
          Biological Clocks
• Internal timing mechanisms
  – Trigger shifts in daily activity
  – Help induce seasonal adjustments

• Phytochrome is part of the switching
 mechanism
  – Blue-green plant pigment

                                         42
                     long day                short night


Phytochrome
    and       short day              long night

 Flowering
                                pulse of white light




                                pulse of red light




                          10 minutes of far-red light
                          follows pulse of red light



                                                           43
      Control of Abscission
• Abscission
  – Dropping of flowers, fruits, or leaves
• What brings it about?
  – Auxin production declines
  – Cells in abscission zone produce ethylene
  – Enzymes digest cell walls that attach leaf
    or fruit to plant
                                                 44
              Senescence
• Sum total of processes that lead to death
 of a plant or some of its parts
• Factors that influence senescence:
  – Decrease in daylight is recurring factor
  – Wounds, drought, or nutritional deficiencies
    can also bring it about

                                               45
            Dormancy
• A predictable period of metabolic
  inactivity
• Short days; long, cool nights trigger
  dormancy
   – Experiments have shown that exposure to
     light blocks dormancy
   – Demonstrates involvement of
    phytochrome
                                               46
       Breaking Dormancy
• Seeds and buds respond to
 environmental cues by resuming growth
• May require exposure to low
 temperatures for some interval
• Probably involves gibberellins and
 abscisic acid
                                       47
Flowering Time




                 48

								
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