Plant reproduction (PowerPoint)

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					    Plant reproduction
•   plants have two choices for reproduction: asexual and
•   asexual reproduction – vegetative growth
     –   portion of the plant is taken from the mature sporophyte
         and used to create a brand new plant
                                                                                                               Germinated pollen grain
     –   this results in a genetically identical progeny                                    Anther             (n) (male gametophyte)
     –   this is an advantage if the plant shows superior qualities
           •   e.g. McIntosh apple                                                          Pollen             Ovary
           •   e.g. varietal grapes                                                         tube               Ovule
                                                                                                               Embryo sac (n) (female
     –   or a disadvantage because there is no genetic variability                                             gametophyte)
         which is crucial for the health of the plant as a species
•   sexual reproduction – production of sex gametes
                                                                                                         Egg (n)
    followed by their fusion and the creation of an embryo                                 Mature Sperm (n)
    that is reliant upon the female gametophyte                                            sporophyte
                                                                                           plant (2n)       (2n)
     –   diploid sporophyte produces haploid spores via meiosis                                         Seed
     –   the spores divide by mitosis to generate a gametophyte             Haploid (n)

     –   the gametophyte contains the small male and female                 Diploid (2n)
                                                                                                                        Embryo (2n)
         haploid plants that produce gametes                                                                            (sporophyte)
     –   fertilization results in the production of a diploid zygote                        seed                 Simple fruit
         which eventually becomes a diploid sporophyte via             Simplified angiosperm life cycle
          Flowers                                                                                Stamen
                                                                                                                 Anther       Stigma      Carpel
•   flowers – reproductive shoots of the angiosperm sporocyte                   Filament                                          Ovary
•   composed of four whorls of floral organs: sepals, petals, stamens and carpels
     –   pistil – single carpel or a fused carpel
•   complete flowers have all four of these floral organs
     –   all have functional stamens and pistil
•   incomplete flowers lack one or more                                                                   Petal
     –   some have functional reproductive parts                                                  Key

     –   most incomplete flowers have either a stamen or a pistil                                 Haploid (n)
                                                                                                  Diploid (2n)
           •   stamens – staminate flowers
           •   pistil – pistillate flowers or carpellate                                                An idealized flower

•   flowers can be described using the following:
     –   1. symmetry – bilateral symmetry: the flower can be divided into two equal parts by an
         imaginary line
                  –   e.g. orchid
           •   radial symmetry – sepals, petals, stamens and carpels radiate out from a center
                  –   e.g. daffodil
     –   2. ovary location – superior ovary: ovary is located above the receptacle
           •   inferior ovary – located within the receptacle
           •   semi-inferior – in between
     –   3. floral distribution – vary from individual flowers to clusters of flowers called
           •   e.g. sunflower – center is an aggregation of incomplete flowers that do not develop
           •   in each undeveloped flower are the male and female reproductive parts of the flower or they may be
     –   4. reproductive variations – presence of staminate and carpellate flowers on the same plant is
         a monoecious plant (bisexual)
           •   presence of either staminate or carpellate flowers– dioecious plant (unisex)
Flower types
•   composite flowers
•   well represented in your own backyard
•   chicory, dandelion, mums, sunflowers, dahlias,
    zinnias, lettuce, Black-eyed Susan
•   the composites have miniaturized each flower
    and then pack them next to each other on a
•   some composite flowers are composed of ray
    and disc flowers, some just one type

                                                     disc flower   ray flower
•   Echinacea blossoms such as the one at the left are typical
    members of the Composite Family
•   However, certain features do distinguish them from all other
•   For example, you can see that Echinacea's central ray flowers
    are distributed over a hill-like receptacle, making the cluster
    of ray flowers look a little like a porcupine. Most composite
    blossoms have flat or only slightly elevated receptacles. Also
    in that picture notice that the involucral bracts are long and
    slender, green, stiff, and pointed downward. The involucral
    bracts of most composite blossoms are more triangular, closer
    packed with one another, and pointed upward, not downward.
•   At the left you see more special features that make an
    Echinacea flower an Echinacea flower. First, notice that the
    ray flower bears no stigma. That's because in Echinacea the
    ray flowers are sterile. They don't have functional female
    parts and therefore the item at the base of the flower does not
    develop into a seed-like achene. In Echinacea the ray flower is
    strictly for drawing attention to the flower by pollinators. Ray
    flowers of many composite blossoms do produce viable
    achenes, and thus do have conspicuous stigmas.
•   Echinacea disk flowers have two unusual features. First,
    notice the large, stiff, orange-tipped, scoop-shaped
    receptacle bract partially folding around the flower. Many
    composite blossoms have no receptacle bract at all, and the
    vast majority of those who do have bracts that are much
    smaller, softer, and pale to transparent. In fact, when you look
    at an Echinacea blossom's center, the pointed things you think
    must be the disk flowers are actually bracts. Remember that in
    flowers a bract is a modified leaf.
•   Mums, or Chrysanthemums, are classic composites -- they are "composite
    flowers". In other words, the mum blossom at the right is actually a collection
    of hundreds of flowers. Each tiny, orange bump in the flower's center is the
    top of a disk flower. Each white "petal" is a ray flower. Each of the many
    disk and ray flowers at the right bears a regular blossom's male and female
•   When we speak of mums, we're referring to any of many species belonging to
    the genus Chrysanthemum, of which there are well over a hundred. The word
    "Chrysanthemum" is both the Latin name and the English name, which often is
    not the case.
•   If you make a cross-section of the above flower, here is what you see:

                This picture shows how the disk flowers are stacked on their bottoms atop the platform-like receptacle. At the right you can see
                that better. Also, at the base of each disk flower you can see the future "seeds," which are actually special composite-flower fruits
                known as achenes. Once the flowers are pollinated, the achenes will enlarge and harden. When you buy "mum seeds" for sowing
                in your garden, you buy those achenes.
                As is typical of composite flowers, the Chrysanthemum's flower heads arise from a cuplike collection of scale-like bracts, like the
                ones at the right. In some composite species the bracts are very slender and in others very wide, sometimes they are other than
                green, and sometimes they are arranged in just one series so that they stand side-to-side instead of overlapping like those above.
•   in angiosperms, pollination is the transfer of pollen from an anther to a stigma
•   process of pollination requires pollinators – agents that carry or move pollen grains from the anther to the
    stigma of the carpel
•   flower traits that attract different pollinators are known as pollination syndromes
•   many ways to pollinate a female stigma
         2. water
     –   3. insect
     –   4. animal
•   biotic pollination: pollination by animals (organisms)
     –   80% of all pollination is biotic
     –   entomophily – pollination by insects
            •   e.g. bees, wasps, ants, beetles, moths and butterflies
     –   zoophily – pollination by animals
            •   e.g. birds and bats

•   abiotic pollination: pollination by non-animal factors
     –   Amenophily – pollination by wind (98% of abiotic pollination)
     –   Hydrophily – pollination by water (aquatic plants)
•   pollination in agriculture – seeks to protect and enhance present pollinators
     –   often involves the culture and addition of pollinators to crops – e.g. commercial fruit orchards
     –   largest manage pollination event is the California almond orchard industry – nearly 50% of all US produced honey
         bees are trucked to these orchards each spring (one million hives)
     –   New York‟s apple crop requires 30,000 hives and Maine‟s blueberry crop requires 50,000 hives each season
     –   bees are also brought to commercial crops of cucumbers, squash, melons, strawberreis
     –   bee species other than honey bees are also used – e.g. bumblbees – greenhouse tomatoes
•   ecology and financial importance – insect pollination improves yield and quality
     –   the vicinity of a forest or wild grasslands can improve yields of apples, almonds and coffee by 20%
•   pollination also requires consideration of the pollenizer
     –   pollinator = agent that moves the pollen
     –   pollinizer – the plant that provides the pollen
     –   some plants are self-fertile or self compatible and can pollinate themselves
     –   other plants have chemical or physical barriers to self pollination and need to be cross-pollinated
•   therefore pollination can be either through: cross-pollination or self-pollination
•   in monoecious plants – there are mechanisms that ensure the male does not pollinate the
    female on the same flower or plant
     – recognition factors that prevent self-fertilization – ensures genetic variability
          • may be similar to an “immune system” in the plant
          • recognizes “self” in the proteins displayed on the pollen
          • this system would reject “self” – opposite to the animal immune system
          • S-proteins on the pollen grains are recognized by proteins on the surface of the stigma
          • dozens of alleles for the S genes exist – similar alleles will be recognized as “self” and rejected
          • self-recognition blocks the formation of the pollen tube and can occur through on of two molecular
          • 1. gametophyte self-incompatability
          • 2. sporophyte self-incompatability
     – self-incompatability – the ability of a plant to reject its own pollen and the pollen of closely
       related individuals
          • gametophyte self-incompatability – S allele in the pollen grain governs the blocking of fertilization
                –   parental sporophyte – genome = S1S2 gives rise to pollen grains that are S1 or S2 classification
                –   an S1 pollen grain will not fertilize an S1S2 egg but will fertilize an S2S3 flower while the S2 pollen grain will
                    not fertilize either
                –   involves the enzymatic destruction of the RNA within the pollen tube – RNA degradaing enzymes called
                    RNases are produced by the cells of the style and enter the pollen tube to destroy the male‟s RNA and induce
                    programmed cell death in the pollen grain
          • sporophyte self-incompatability – fertilization is blocked by S-allele gene products in tissues of the
            parental sporophyte that adhere to the pollen wall
                –   neither an S1 or S2 pollen grain will fertilize an S1S2 flower or an S2S3 flower
                –   signal transduction pathways located in the epidermal cells of the stigma – prevents germination of the pollen
– some plants prevent self fertilization by developing stamens and
  pistils at different times or arrange these reproductive parts in
  such a way that the animal pollinator cannot accidently transfer
  pollen within the flower or plant
   • development of two types of flowers – “pin” and “thrum”
   • pin flowers – long styles and short stamens
   • thrum flowers – short styles and long stamens
– dioecious plants cannot self fertilize –because they only possess
  one type of reproductive structure
                                        Stigma                                        Stigma


                                                 Pin flower            Thrum flower
         Self-pollination vs. Cross-pollination
•   cross-pollination – between a pollinator and an external pollinizer
     –   also called syngamy
     –   pollen is delivered to a flower of a different plant
     –   plants adapted to cross-pollinate have taller stamens than the carpels – e.g. thrum type
     –   e.g. apple crops – due to the grafting of most apple species – gives rise to a genetically
         identical orchard
            •   therefore, each apple stigma would recognize “self” and reject the pollen
            •   therefore different apple sporophytes with different S alleles must be used
            •   alternatively – a crabapple limb is grafted to every fifth or sixth tree – genetic variation
•   self-pollinization – pollen moves to the female part of the same flower or to
    another flower on the same plant
     –   also called autogamy
     –   self pollination is restricted to those plants that accomplish pollination without an external
            •   e.g. stamens actually grow in contact with the pistil
     –   plants adapted to self-pollinate have stamens and carpels at the same length
     –   cleistogamy – pollination that occurs before the flower opens
            •   flower is called a cleistogamous flower
            •   these flowers MUST be self compatible or self-fertile
     –   many crop plants are self-pollinating
            •   peas, corn and tomatoes
            •   routinely self-pollinate
            •   to prevent self-fertilization – laborious removal of the anthers or through the development of sterile
                male plants
            •   most peach varieties are autogamous – but not truly self-pollinated because the insect transfers
                pollen to another flower on the same plant
                    –    cross-pollination can give a better crop
                    –    most crops are self-fertilized
     –   hybridization – effective pollination between flowers of different species (within the
         same genus) or even between flowers of different genera (e.g. orchids)
            •   many farmers wish to improve their crops by combining genes with other superior plants
            •   creation of hybrid seeds
    Pollination and Honey bees
•    Andrena bee
•    collect nectar from the flower which is later converted in the hive to honey
•    pollen grains are also collected and stored on the hind legs of the bee – as a collection
     called a pollen basket
•    nectar provides the energy for bee pollination
•    pollen provides the protein
•    so bees will deliberately collect pollen to meet the growing nutritional needs of the
     “building” hive
•    a bee that is intentionally collecting pollen for its growing hive is up to 10X more
     effective of a pollinator than one intentionally gathering nectar for the mature hive
•    so good hive management will ensure that the hives are in the building or brood stage
     during the bloom period of a crop
•    number of hives per acre of crop
      –   apples – 1-2
      –   blueberries – 4
      –   cantaloupe – 2-4
      –   cucumber – 1-2
      –   squash – 1
      –   watermelon – 1-3
•   successful pollination leads to the generation of a pollen tube,
    the discharge of sperm and the fertilization of the egg leading
    to the formation of the embryo                                  Development of a male gametophyte                                                       Development of a female gametophyte
•   the anther contains pollen sacs (microsporangia) in which (pollen grain)                                                                                (embryo sac)

    diploid micropore mother cells undergo meiosis to generate 4
    haploid microspores
     –    each has the potential to develop into the male gametophyte                      Pollen sac
     –    each microspore undergoes mitosis and cytokinesis to create two
          separate cells: generative cell and tube cell
          these two cells + spore wall = pollen grain                                                                                                            sporangium

     –    spore wall is unique to the species of plant that creates it                      Micro-
                                                                                            sporocyte                                                            Mega-
     –    during maturation of the male gametophyte – the germinative cell                                                                                       sporocyte

          passes into the tube cell                                                                                           MEIOSIS                            Integuments
     –    the tube cell produces the pollen tube and as it elongates the                                                                                         Micropyle
          germinative cell divides to form two sperm cells                                  Micro-

                                                                                            spores (4)
    the ovary contains multiple ovules                                                                                                                           Surviving
     –    each ovule contains a megasporangium which houses the diploid                                                                                          megaspore

          megaspore mother cells that undergo meiosis to produce 4                          Each of 4
          haploid megaspores                                                                microspores                                                   Female gametophyte
                                                                                                                                                             (embryo sac)
     –    the subsequent steps can vary from species to species                                                               MITOSIS
                                                                                                                                                  Ovule          Antipodal
     –    in most angiosperm species only one MG survives                                                                                                        cells (3)

     –    its nucleus divides three times without cytokinesis to give rise to               Generative
                                                                                            cell (will
                                                                                                             gametophyte                                         Polar
          one large cell with 8 haploid nuclei                                              form 2
                                                                                                             (pollen grain)                                      nuclei (2)

     –    membranes than form and divide these nuclei up to form the                                                                                             Egg (1)
          complete female gametophyte or the embryo sac
                                                                                                                                                                 Synergids (2)
          within the embryo sac is:                                                                          Nucleus of
                                                                                                             tube cell
             •   three antipodal cells- at one end of the sac, function unknown
                                                                                                          20 µm
             •   two polar nuclei – not partitioned but share the cytoplasm of the large
                 central cell of the embryo sac                                                                   Ragweed
                                                                                                                             to labels
             •   2 synergids – the other end of the sac, flank the egg and function to                            grain                                         Embryo
                                                                                                                  (colorized                                    sac
                 attract the pollen tube to the egg                                           75 µm

                                                                                                                                              100 µm
                                                                                                                  SEM)         Haploid (n)
             •   1 egg                                                                      (LM)
                                                                                                                               Diploid (2n)                     (LM)
         Double Fertilization
•   after landing on a receptive stigma – the pollen grain absorbs moisture and
    begins to germinate (grow)
•   it produces its pollen tube that extends down between the cells of the style
    toward the ovary and the ovules
•   mechanism of this tube growth is only being elucidated
     –   presence of a chemoattractant(s) is likely to guide the pollen tube through the style and
         toward the ovary
     –   role of calcium??
•   the tip of the tube enters the ovary and two sperm are discharged through the
    micropyle in the grain (a gap between the integuments of the ovule)
•   the fertilization that results is unique to the angiosperm = double fertilization
     –   one fertilization event is the typical union of a sperm with an egg to produce the
         zygote which divides to form the embryo
     –   second fertilization event involves the union of the second sperm with the two polar
         nuclei – forms a triploid nucleus in the center of the ovule
     –   this triploid cell gives rise to the endosperm – food storing tissue of the seed
•   after double fertilization, the ovule develops into the seed (embryo, endosperm
    and integuments)
     –   endosperm development – usually precedes embryo development
            •   the triploid nucleus divides and produces a multinucleate “supercell” with a milky consistency
            •   cytokinesis then converts the multinucleate cell into a multicellular endosperm
            •   these “naked” cells will eventually produce cell walls and the endosperm will become solid
            •   the “milk” of the coconut is an example of liquid endosperm and the “meat” is an example of a
                solid endosperm
            •   if the endosperm is used during the development of the cotyledons then the seed will lack an
                endosperm as it matures
     –   embryo development – first mitotic division of the zygote results in an embryo
            •   splits the zygote into a basal cell and a terminal cell
            •   terminal cell gives rise to most of the embryo
            •   the basal cell continues to divide transversely and produces a thread of cells = suspensor
            •   the suspensor is the “umbilical cord” anchoring the embryo to its parent
            •   functions in the transport of nutrients to the embryo from the parent
            •   in some plants the suspensor functions in the transfer of nutrients from the endosperm
                      grain     Stigma

                                Pollen tube

          If a pollen grain     2 sperm
 germinates, a pollen tube
    grows down the style
        toward the ovary.

                                Ovule (containing
                      Polar     gametophyte, or
                                embryo sac)


                                Polar nuclei
           The pollen tube      Egg
discharges two sperm into
   the female gametophyte       Two sperm
    (embryo sac) within an      about to be
                    ovule.      discharged

       One sperm fertilizes
       the egg, forming the     Endosperm
  zygote. The other sperm       nucleus (3n)
     combines with the two      (2 polar nuclei
          polar nuclei of the   plus sperm)
         embryo sac’s large
      central cell, forming a
 triploid cell that develops    Zygote (2n)
    into the nutritive tissue   (egg plus sperm)
         called endosperm.
• the terminal cells divides multiple times to produces a spherical proembryo
  attached to the suspensor
• the cotyledons begin to form as bumps on the proembryo
    – eudicot is heart shaped at this stage
    – in the monocot only one of these bumps will go on to form a cotyledon





                         Terminal cell
                         Basal cell

                                      Suspensor                 Seeds
                Basal cell


        Shoot apex

         Root apex
                                         Seed coat
•   after the rudimentary cotyledons form – the embryo
    elongates                                                                                                  Seed coat
     – cradled between the two cotyledons in the eudicot is
       the embryonic shoot apex including the shoot apical
       meristem                                                                                                 Cotyledons
     – at the other end of the embryo where the suspensor                                                        Epicotyl
       attaches is the root apex with its RAM
     – the seed develops specific structures depending on
       whether it is a monocot or a eudicot                                                                     Radicle
            • eudicot – bean                                                           Castor bean, a eudicot with thin cotyledons
                  – elongated embryo – embryonic axis
                  – contains two developing cotyledons attached to the
                    embyro                                                                  Seed coat                 Epicotyl
                  – below where these cotyledons attach to the embryo –
                  – the hypocotyl terminates in the radicle – embryonic root                                           Hypocotyl
                  – above the attachment of the cotyledons is the epicotyl –
                    shoot tip with a pair of miniature leaves                                 Radicle
                  – the majority of the bean is the starch-filled cotyledons
                    (food source)                                                                                      Cotyledons
            • eudicot – castor bean
                  –   reduced cotyledons in size
                  –   retain their food supply in the endosperm rather than the     Common garden bean, a eudicot with thick cotyledon
                  –   the cotyledons receive their nutrition from the endosperm
                      and transfers it to the rest of the embryo as it grows                                                Pericarp fused
            • monocot – corn kernel                                                              (cotyledon)                with seed coat
                  – single cotyledon
                  – in the grass family (including corn and wheat) – the                                                    Endosperm
                    cotyledon is specialized and forms a scutellum                              Coleoptile
                  – the embryo of grasses is enclosed within two shields:
                    coleoptile which covers the shoot and the coleorhiza                                                    Hypocotyl
                    which encloses the young root                                               Coleorhiza
•   during the last stages of seed maturation – the seed dehydrates until                                                   Radicle
    about 5-15% total water content and becomes covered by the
    integuments which have hardened into a seed coat                              Maize, a monocot
     –   the cotyledons and embryo become dormant
•   while the seed is developing from ovules, the fruit is developing from the ovary
•   fruit = ripened ovary + seeds of a flowering plant
•   fruit protects the developing seeds and will participate in their dispersal using wind or animals
•   two main types of fruits: dry and fleshy
•   dry fruits
     –   the ripening of a dry fruit involves the aging and drying of the fruit tissues
•   fleshy fruits – a complex series of hormonal changes results in an enticing edible fruit that attracts animals
     –   the fruits pulp becomes softer due to enzymes that digest components of the cell wall making the flesh of the fruit softer
     –   usually a color change from green to another color
     –   organic acids and starch increase in concentration – sweet or tart fruit

•   fertilization of the egg triggers a series of hormonal events that triggers the development of the ovary into the fruit
•   as the fruit develops, the other parts of the flower die and drop away
     –   tip of the pea pod is the remnant of the stigma
•   the fruit ripens about the same time the seed has finished its development
     –   accelerated through the production of ethylene
•   pollination precedes fertilization – therefore fruit development is usually a sign of pollination
•   as the fruit develops the outer wall of the ovary thickens and develops into the pericarp
     –   tissue that develops and surrounds a seed
     –   develops from the wall of the ovary
     –   in some fruits the pericarp can become dry and hard and form a shell
•   in fleshy fruits the pericarp can be divided into several regions:
     –   exocarp – or epicarp
            •   tough outer skin of the fruit or the peel
     –   mesocarp – or sarcocarp
            •   botanical term for the succulent and fleshy middle layer of the pericarp
            •   usually the part of the fruit that is eaten
     –   endocarp – hard inner layer of the pericarp of some fruits that contains the seed
     –   very noticeable in the cherry family, the apricot family, the plums
     –   it is the pit!
          Types of fruits                                                                    Stamen           Ovary
•   several types of fruits depending on their developmental origin                                            Ovule
     –   1. simple: derived from a single carpel or several fused carpels                             Pea flower

         within one pistil                                                                                Seed
           •   can be either fleshy or dry
           •   the dry fruits can either be dehiscent (opening to discharge seeds) or
               indehiscent (not opening to discharge seeds)                                           Pea fruit
           •   if the pericarp is fleshy – fruit is known as a simple fleshy fruit             Simple fruit
           •   e.g. apple, peach, pea, wheat, coconut, nuts, carrot, radish, beet,
               tomato, avacado                                                                               Carpels
     –   2. aggregate – results from a single flower that has more than one
         separate carpel with each forming a separate “fruitlet”
           •   develops from multiple simple pistils with one carpel each                                     Stamen
           •   the fruit is frequently called a “druplet” (raspberry) or a bramble
               (blackberry)                                                                    Raspberry flower

     –   3. multiple – develops from an influorescence (a group of flowers              Carpel             Stigma
         tightly clustered together) – the walls of the ovaries thicken and             (fruitlet)         Ovary
         fuse together                                                                  Stamen
           •   e.g. pineapple, mulberry, breadfruit
     –   there are fruits in which structures other than the ovary contribute                 Raspberry fruit
         to the formation of the fruit                                                    Aggregate fruit
           •   these fruits are called accessory fruits or false fruits
           •   e.g. apple flowers – the ovary is embedded in the receptacle (inferior
               ovary) and the fleshy part of the fruit is derived mainly from the                                 Flower
               enlargened receptacle
                  –   only the apple core develops from the ovary
           •   e.g. fig
           •   e.g. strawberry                                                                 Pineapple inflorescence
                          -aggregate accessory fruit consisting of an enlargened          Each
               receptacle embedded with tiny one-seeded fruits contained with             segment
               achenes – outer surface of the strawberry                                  develops
                                                                                          from the
                                                                                          of one
                                                                                                  Pineapple fruit
                                                                                              Multiple fruit
•   Fragaria
•   more than 20 named species
•   many hybrids and cultivars (plant that has received a name under the
    International Code for Nomenclature of Plants)
•   most common are cultivars of the Garden strawberry – Fragaria ananassa
•   accessory aggregate fruit – the fleshy part is derived from the peg at the
    bottom of the hypanthium – that holds the ovaries
•   so the seeds on the outside are the actual fruits with the flesh of the
    strawberry a modified receptacle
•   classification of the strawberry species is based on the number of
•   7 basic types of chromosomes that each species has in common
•   but each species may exhibit different polyploidy
     –   some species are diploid (14 chromosomes), others triploid, tetraploid, hexaploid,
         octoploid or decaploid
                                                                                              Kingdom:     Plantae
•   the more chromosomes the more rubust the plant is
•   strawberries can reproduce asexually through above ground stems called                    Division:    Magnoliophyta
    stolons – new plants will form at the nodes and will develop root structures              Class:       Magnoliopsida
•   many strawberry species do not have male reproductive structures
     –   some have only female and some species are monoecious                                Order:       Rosales
     –   these female only plants are pollinated by the monoecious ones                       Family:      Rosaceae
                                                                                              Subfamily:   Rosoideae
                                                                                              Genus:       Fragaria
                                                                                                            Coconut, meat, raw
•   coconut – fruit not a nut but a seed                                                                 Nutritional value per 100 g
•   known as a fibrous drupe – not a true nut
•   husk = mesocarp composed of fibers called coir                                                       Energy 350 kcal 1480 kJ
     –    coir is used to make rugs, mats, brushes, potting
•   inner stone = endocarp with three germination                                                                                  15.23
    pores at one end, contains the endosperm which                                                                                 g
    is edible
                                                                                                   - Sugars                        6.23g
•   one of these pores will allow the growth of the
    embryonic root – the radicle                                                                   - Dietary fiber                 9.0 g
•   mature coconut fruits drop from trees and can
    appear dead for months until a small green shoot                                                                               33.49
    pushes out from the coconut                                                                    Fat
     –    many changes prior to this emergence
     –    at the end where the three „eyes‟ are located – the                                      Protein                         3.3 g
          embryo begins to grow
          the embryo feeds off of the “milk” (liquid
          endosperm – coconut water) and the “meat”
          (solid endosperm = testa)
                                                                     Fruits                        Thiamin (Vit. B1) 0.066

     –    the embryo fills the space within the seed                                               Riboflavin (Vit. B2) 0.02
•   the embryo will sprout out of the shell and will            -flowers of the coconut palm are   mg
    become a young coconut seedling
•   one large coconut (unripe) can contain up to 1              polygamomonoecious                 Niacin (Vit. B3) 0.54 mg        4%
    liter of coconut water                                      (both male and female parts in
•   water is a combination of sugar, fibre, proteins,           the same influorescence)           Pantothenic acid
    anti-oxidants and vitamins                                                                     (B5) 0.300 mg
     –    can be used as an IV fluid!
                                                                -flowering occurs continuously
•   coconut milk = combination of grated coconut                with the female flowers            Vitamin B6 0.054 mg             4%
    flesh + warm water to extract out the aromatic              producing the seeds                Folate (Vit. B9) 26 μg          7%
    compounds and oils
•   if left to set the coconut cream will rise to the top
                                                                -most are cross-pollinated         Vitamin C 3.3 mg                6%
•   the sap can be harvested and fermented to
    produce palm wine or “toddy” or can be boiled to                                               Calcium 14 mg                   1%
    produce a sweet syriup                                                                         Iron 2.43 mg                    19%
•   interior of the growing true stem can be harvested
    and eaten – heart-of –palm (kills the stem)                                                    Magnesium 32 mg                 9%
•   the meat can be dried to form copra – main                                                        Percentages are relative to US
    source of coconut oil                                                                          Phosphorus 113 mg                 16%
                                                                                                       recommendations for adults.
•   coconut roots can be used as a dye                                                               Source: USDA mg
                                                                                                   Potassium 356 Nutrient database8%
•   the trunk can be harvested for palmwood
                                                                                                   Zinc 1.1 mg                     11%
Seedless fruits
• seedlessness is an important feature of many commercial fruit crops
• bananas, pineapples, grapes, watermelons, some citrus fruits (navel
  oranges, tangerines)
• in some species, seedlessness is the result of parthenocarpy = fruits set
  without fertilization
    – may or may not require pollination
• most species require some sort of pollination stimulus
    – pollination triggers fruit development within the ovary but the ovules
      abort the embryos and do not produce mature seeds (stenospermocarpy)
• some fruits will become seedless if the plant does not undergo
  pollination but will develop seeds if pollination takes place and results
  in fertilization within the ovules
    – e.g. pineapple, cucumber
• seedless watermelons are grown from seeds – seeds are produced by
  hybridizing diploid and tetraploid lines of watermelons – resulting
  seeds are sterile triploid plants with no reproduction
    – fruit development is triggered by pollination but no fertilization takes
      Bananas and Plantains
•   originated in the Indo-Malaysian region to northern Australia
•   banana = seedless fruit produced from triploid plants
•   plant possesses three sets of chromosomes
•   this prevents meiosis and the plant does not generate mature gametes for
    sexual reproduction
•   such plants can arise from spontaneous mutations or through hybridization
    between diploid and tetraploid individuals
•   the banana is usually propagated vegetatively through the production of
    “pups” – offsets that are genetically identical to the parent
     –    grow off of the rhizomes
     –    large pups are preferred as planting materials
•   grow from underground rhizomes with fleshy pseudostems that grow
    vertically above ground
•   the true stem forms 10-15 months after planting and pushes through the
    pseudostem/stalk producing the terminal influorescences that will produce
    the fruit
•   each banana stalk produces one huge flower cluster and then dies
•   new stalks grow from the rhizome
•   flower – shoots out from the tip of the true stem as a single structure
•   is a large purple-clad bud – as it opens slim, nectar rich white flowers appear
    as a whorled cluster with a deep red bract covering them
•   the flowers of the first 5 to 15 rows are female – the develop without
    pollination to form clusters of fruits called hands – technically a berry
     –    these produce the fruits
•   as the influorescence elongates – sterile flowers with abortive male and
    female parts now arise, followed by normal staminate flowers and carpellate
    flowers with abortive ovaries
•   as a seed matures it dehydrates and enters a dormancy phase – low metabolic rate in the embryo and a
    suspension of its growth and development
•   conditions required to break this dormancy varies from plant to plant
     –     e.g. once they reach a suitable environment
     –     e.g. some require a specific environmental cue
•   seed dormancy increases the chances that the seed will germinate under favorable conditions
•   environmental conditions
           desert plants – require substantial amounts of water
           trees – heat provided by fires
                                                                                                              Seed germination
     –     extended exposure to cold
     –     lettuce – requires increased light
•   germination depends on the physical process called imbibition
     –     uptake of water due to the lower water potential of the dry seed
     –     causes the seed to expand and rupture its coat
     –     also triggers metabolic events in the embryo that enables it resume its development
     –     as the embryo grows it makes digestive enzymes which digests away the stored foot in the seed (endosperm or cotyledons)
     –     first organ to emerge is the embryonic root – the radicle
     –     the shoot tip then forms and breaks through the soil surface
     –     in many eudicots and beans – a hook forms in the hypocotyl and this hook is pushed through the soil – stimulated by light to
           straighten which raises the cotyledons and the epicotyl
              •    the shoot apex is actually pulled upward rather than being pushed tip first through the abrasive soil
              •    the epicotyl spreads its first leaves which are called true leaves as apposed to the “seed leaves” or the cotyledons
     –     in monocots breaking ground is accomplished by the coleoptile
              •  the sheath enclosing the coleoptile pushes upward through the soil and into the air
              •  the shoot tip grows through the tunnel forming within the growing coleoptile
              •  the shoot then breaks through the tip of the coleoptile
                      Foliage leaves
                                                 Epicotyl                                                                       Foliage leaves
                   Cotyledon                      Cotyledon
         Hypocotyl                                                                             Coleoptile            Coleoptile

                      Seed coat
    Common garden bean                                                                     Maize
•   to ensure successful germination of a seed and embryo – the conditions must be very favorable
•   some plants will produce numerous seeds in order to ensure survival of a few embyros
•   this is very expensive energy wise
•   some plants reproduce asexually and produce an exact copy of themselves
•   does not allow for genetic recombination
•   result is essentially a clone
•   in seedless plants, some gymnosperms and some angiosperms – reproduction can be either sexual or asexual
•   if a plant is superbly adapted to one environment and is very successful – then asexual reproduction would be
    advantageous – if the environment remains the same
•   also known as vegetative reproduction
•   is an extension of the capacity for indeterminate growth owing to the presence of meristematic tissues
•   in addition the parenchyma of some tissues can specialize and divide to create different kinds of tissue
•   fragmentation – separation of a parent plant into parts the develop into whole plants
     –   one of the most common modes of asexual reproduction
     –   e.g. root system – branches off to form adventitious roots which give rise to separate shoot systems and separate plants
     –   produced the oldest known plant clone – creosote bushes of the Mojave desert
•   production of bulbs
•   production of suckers from exisiting root systems
•   apomixis – “away from the act of mixing”
     –   production of plants asexually
     –   reproduction of dandelions
     –   produce seeds without pollination or fertilization
     –   diploid cell in the ovule gives rise to the embryo and the ovule matures into seeds
     –   seeds are dispersed as windblown fruits
     –   e.g. dandelions, Kentucky bluegrass
          Vegetative growth and agriculture
•   cuttings – many houseplants, woody ornamental plants and orchard trees
     –   asexually reproduced from plant fragments called cuttings
     –   some cuttings come from the shoot or stem
     –   at the cut end of the shoot – mass of undifferentiated cells forms – callus
     –   from this callus is the development of adventitious roots
     –   if the plant is cut at a node – no callus forms but adventitious roots still do
     –   the African violet can be propagated from single leaves
     –   the potato can be cut into several pieces each containing a vegetative bud of “eye”
         that regenerates a whole plant
•   grafting – modification of reproduction from cuttings
     – a twig or bud of one plant is grafted onto a plant of a closely related species or the
       same species
     – combines the best qualities of plants
     – usually done when the plant is young
     – the plant that provides the root system = stock
     – the twig grafted onto the stock = scion
     – e.g. grape varietals
     – e.g. dwarf trees – made by grafting normal twigs onto the stocks of dwarf varieties
           • the dwarf quality retards the normal growth of the twig – dwarf plant
•   test-tube cloning – in vitro methods to create and clone plants
     – culturing of small pieces of tissues cut from a parent plant = explant
     – explant is cultured on artificial media containing the nutrients and hormones
       required to grow the plant
     – explant can very from single parenchyma cells to pieces of tissue
     – a callus will form and sprout shoots and roots
     – test tube plantlets are then transferred to soil
     – can also subdivide the callus and increase the number of plantlets that result
     – e.g. orchids, pine trees with high wood production
     – protoplast fusion – tissue culture methods are used to invent new plant varieties that
       can be cloned
          •   cell wall is removed through treatment with enzymes (cellulases and pectinases)
          •   produces the protoplast – screened in the lab for the desired genes
          •   two protoplasts are fused in the lab to produce a new one
          •   the new protoplast regenerates a wall and can be cultured into a callus

                                                Just a few                 The callus
                                                parenchyma cells           differentiates into
                                                from a carrot gave         an entire plant,
                                                rise to this callus,       with leaves, stems,
                                                a mass of                  and roots.
•   artificial selection – the process of selecting for specific, desired traits in an organism
     –   corn – “unnatural monster” created by humans
           •   modern corn would become extinct without our interference
           •   corn kernels are permanently attached to the central axis (“cob”) and are protected by a tough
               overlappng leaf sheath (“husk”
           •   this results in a plant that cannot scatter its kernels and reproduce
           •   corn was first domesticated around the Neolithic age – late Stone age
     –   but selection can be natural
           •   wheat – result of natural hybridization between different species of grasses
           •   quite common between plants and can be exploited by farmers for crop improvement and horticulturists
           •   e.g. corn – most common varieties of corn are poor sources of protein
                  –   proteins very low in lysine and tryptophan
                  –   these are two of the 8 essential amino acids in humans
                  –   40 years ago – discovery of a mutant corn variety called opaque-2
                  –   this variety had high levels of these two essential amino acids
                  –   but this strain also had a soft endosperm within its seed – vulnerable to attack from pests and hard to harvest
                  –   over the next 20 years – strain acquired a harder endosperm while retaining the amino acids
                  –   can be accomplised easily now using genetic engineering!!
•   transgenes – introduction of a new gene into the genome of the plant = GM plants
    (genetically manipulated)
     –   many of these genes are used to increase yields on difficult land conditions
     –   e.g. cotton, corn, potatoes
           •   contain genes from many types of bacteria – e.g. Bacillus strains
           •   e.g. introduction of the gene for Bt toxin into plants can help control pest induced damage
     –   some plant species have genes that make them tolerant to a number of herbicides that kill insects and
         leave the plant intact
           •   e.g. corn, cotton, sugar beets and potatoes
     –   can also engineer plants to be resistant to disease
           •   e.g. papaya resistant to spring rot virus introduced into Hawaiian crops
     –   human health???
           •   may transfer allogenes to humans – genes that produce proteins we are allergic to
           •   but researchers are removing genes from soybeans, peanuts and other crops that are known to cause allergies
           •   Bt corn contains 90% less of the cancer-causing mycotoxin called fumonism (produced by the fungus Fusarium)
           •   labelling demands
           •   but why not naturally produced hybrids???
     –   transgene escape – introducing transgenes into related wild species that do not have the transgene
           •   spontaneous hybridization with wild relatives
           •   not a problem if no wild relatives are nearby – e.g. soybeans
           •   also the use of “terminator” technology – plants undergoing the last stages of seed or pollen maturation produce
               “suicide” genes and will not complete their maturation and reproductive cycle

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