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Pant and its reproduction system
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Plant reproductionPlants have two choices for
reproduction: Asexual Reproduction Sexual Reproduction
Asexual reproduction – vegetative growthPortion of the plant is taken from the mature
sporophyte and used to create a brand new plant
this results in a genetically identical progeny this is an advantage if the plant shows superior
qualitiese.g. Mcintosh applee.g. varietal grapes
Disadvantage because there is no genetic variability which is crucial for the health of the plant as a species
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Sexual reproduction – Production of sex gametes followed by their fusion and the creation of an embryo that is reliant upon the female gametophyteDiploid sporophyte produces haploid spores via
meiosisThe spores divide by mitosis to generate a
gametophyteThe gametophyte contains the small male and
female haploid plants that produce gametesFertilization results in the production of a
diploid zygote which eventually becomes a diploid sporophyte via mitosis
Plant reproduction
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Angiosperms Sexual reproduction involves flowers and seeds. Flowering can be controlled by hormones, genes
and/or environmental factors.Angiosperms produce flowers
Flowers with both male and female reproductive organs are perfect flowers.
Flowers that have only male or only female reproductive organs are imperfect flowers.
Some angiosperms produce separate male and female flowers (imperfect flowers).Monoecious plants Dioecious plants
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Haploid (n)Diploid (2n)
Key
Simplified angiosperm life cycle
Germinatingseed
Seed
Seed
Simple fruit
Embryo (2n)(sporophyte)
Zygote (2n)
FERTILIZATION
Egg (n)
Sperm (n)
Embryo sac (n) (femalegametophyte)
OvuleOvary
Germinated pollen grain(n) (male gametophyte)
Pollentube
Anther
Maturesporophyteplant (2n)
Simplified angiosperm life
cycle
Angiosperms
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FlowersFlowers – Reproductive shoots of the
angiosperm sporocyte.Composed of four whorls of floral organs:
sepals, petals, stamens and carpelsPistil – Single carpel or a fused carpel
Complete flowers have all four of these floral organsAll have functional stamens and pistil
Incomplete flowers lack one or moreSome have functional reproductive partsMost incomplete flowers have either a stamen
or a pistilStamens – Staminate flowersPistil – Pistillate flowers or Carpellate
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Stamen Anther
Filament
An idealized flowerReceptacle
Petal
Carpel
Sepal
Ovary
Style
Stigma
Flowers
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Flowers can be described using the following:
1. Symmetry a. Bilateral symmetry: the flower can be divided
into two equal parts by an imaginary line ,e.g. orchid.
b. Radial symmetry: sepals, petals, stamens and carpels radiate out from a center .e.g. daffodil.
2. Ovary locationa. Superior ovary: ovary is located above the
receptacleb. Inferior ovary: located within the receptaclec. Semi-inferior : in between
Flowers
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Flowers3. Floral distribution – Vary from individual
flowers to clusters of flowers called inflorescences 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 sterile
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)
Flowers
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Copyright reserved. 2012 The E Tutor
Reproductive StructuresReproductive Floral Structures:Stamen – male reproductive structure
Anther – sac where pollen in producedFilament – stalk that supports anther
Carpel (Pistil) – female reproductive structureStigma – sticky area on top of carpel that
receives pollenStyle – tube that connects stigma to ovaryOvary – base of carpel that contains ovule and
egg sac
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Copyright reserved. 2012 The E Tutor
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Stamen Anther Filament
Carpel
StigmaStyle
OvaryOvule
Petal
Receptacle
Sepal all stamens = Androeciumall carpels = Gynoecium
all petals = Corollaall sepals = Calyx
Male structure
Female structure
Reproductive Structures
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Control of FloweringPhotoperiodism – Plant response to light
involving relative lengths of day and night.
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Control of Flowering
Control of Flowering Long-day plants – Bloom when days are longest
and nights are shortest (mid-summer). Short-day plants – Bloom in spring, late summer,
and autumn when days are shorter and nights are longer.
Day-neutral plants – Day-length not important for flowering.
Day length is not as critical as night length in regulation of flowering.
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Control by light is due to a pigment in plants called phytochrome.
Phytochrome – Blue-green pigment that controls various growth responses (including flowering) in plants
Two forms of phytochrome:Pr – Inactive form
Pfr – Active form
Control of Flowering
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Control of Flowering
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Pollination Pollination is the process by which pollen
is placed on the stigma Self-pollination: Pollen from a flower’s anther
pollinates stigma of the same flower. Cross-pollination: Pollen from anther of one
flower pollinates another flower’s stigma.
Self PollinationCross-pollination
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Successful pollination in many angiosperms depends on regular attraction of pollinators
Flowers & animal pollinators have coevolved resulting in specialized relationships
Pollination
-Bees are the most common insect
pollinators
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Flower traits that attract different pollinators are known as pollination syndromes
Many ways to pollinate a female stigma1. Wind2. Water3. Insect4. Animal
Pollination
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Pollination life Cycle
Pollination
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Biotic pollination: Pollination by animals (organisms)80% of all pollination is bioticEntomophily – pollination by insects
e.g. bees, wasps, ants, beetles, moths and butterfliesZoophily – pollination by animals
e.g. birds and bats
Abiotic pollination: Pollination by non-animal factorsAmenophily
Pollination by wind (98% of abiotic pollination)Hydrophily
Pollination by water (aquatic plants)
Pollination
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Self- pollinization – pollen moves to the female part of the same flower or to another flower on the same plantalso called autogamyself pollination is restricted to those plants that
accomplish pollination without an external pollinatore.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 opensflower is called a cleistogamous flowerthese flowers MUST be self compatible or self-fertile
Many crop plants are self-pollinatingpeas, corn and tomatoesroutinely self-pollinate
Pollination
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Pollination
Cross-pollination – between a pollinator and an external pollinizeralso called syngamypollen is delivered to a flower of a different
plantplants adapted to cross-pollinate have taller
stamens than the carpels – e.g. thrum type flower
e.g. apple crops – due to the grafting of most apple species – gives rise to a genetically identical orchard
Pollination
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Fertilization Pollen grain germinates on stigma, a pollen tube
grows down the style and enters the ovule through the micropyle.
The tube cell leads the way through the pollen tube.
The generative cell divides forming 2 sperm which follow the tube cell to the micropyle.
One sperm fuses with the egg to form the zygote (2n),
The other fuses with the polar nuclei to form the endosperm (3n).
This is called double fertilization.
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After double fertilization, the ovule develops into the seed (embryo, endosperm and integuments)Endosperm development – usually precedes
embryo developmentthe triploid nucleus divides and produces a
multinucleate “supercell” with a milky consistencycytokinesis then converts the multinucleate cell into a
multicellular endospermthese “naked” cells will eventually produce cell walls
and the endosperm will become solidthe “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
Fertilization
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Embryo development – first mitotic division of the zygote results in an embryosplits the zygote into a basal cell and a terminal
cellterminal cell gives rise to most of the embryothe basal cell continues to divide transversely
and produces a thread of cells = suspensorthe suspensor is the “umbilical cord” anchoring
the embryo to its parentfunctions in the transport of nutrients to the
embryo from the parentin some plants the suspensor functions in the
transfer of nutrients from the endosperm
Fertilization
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Stigma
Pollen tube
2 sperm
Style
Ovary
Ovule (containing femalegametophyte, or embryo sac)
Micropyle
Polarnuclei
Egg
If a pollen graingerminates, a pollen tube
grows down the style toward the ovary.
Pollengrain
Fertilization
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Ovule
Polar nuclei
Egg
Two spermabout to bedischarged
The pollen tubedischarges two sperm into the
female gametophyte (embryo sac) within an ovule.
One sperm fertilizesthe egg, forming the zygote. The other sperm combines with the two polar nuclei of
the embryo sac’s large central cell, forming a triploid
cell that develops into the nutritive tissue called
endosperm.
Endosperm nucleus (3n)(2 polar nuclei plus sperm)
Zygote (2n)(egg plus sperm)
Fertilization
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Seeds The terminal cells divides multiple times to
produces a spherical proembryo attached to the suspensor
The cotyledons begin to form as bumps on the proembryoEudicot is heart shaped at this stage in the monocot only one of these bumps will go on
to form a cotyledon After the rudimentary cotyledons form – the
embryo elongatescradled between the two cotyledons in the eudicot is
the embryonic shoot apex including the shoot apical meristem
at the other end of the embryo where the suspensor attaches is the root apex with its RAM
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The seed develops specific structures depending on whether it is a monocot or a eudicot Eudicot – bean
elongated embryo – embryonic axis contains two developing cotyledons attached to the
embyro below where these cotyledons attach to the embryo –
hypocotyl the hypocotyl terminates in the radicle – embryonic
root above the attachment of the cotyledons is the epicotyl –
shoot tip with a pair of miniature leaves the majority of the bean is the starch-filled cotyledons
Eudicot – castor bean reduced cotyledons in size retain their food supply
in the endosperm rather than the cotyledons the cotyledons receive their nutrition from the
endosperm and transfers it to the rest of the embryo as it grows
Seeds
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SeedsSeed coat Epicotyl
Radicle
Hypocotyl
Cotyledons
Common garden bean, a eudicot with thick cotyledons
Seed coat
Cotyledons
Epicotyl
Radicle
Hypocotyl
Endosperm
Castor bean, a eudicot with thin cotyledons NM Spirit
Monocot – corn kernel single cotyledon in the grass family (including corn and wheat) –
the cotyledon is specialized and forms a scutellum
The embryo of grasses is enclosed within two shields: Coleoptile which covers the shoot Coleorhiza which encloses the young root
During the last stages of seed maturation – the seed dehydrates until about 5-15% total water content and becomes covered by the integuments which have hardened into a seed coat the cotyledons and embryo become dormant
Seeds
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Maize, a monocot
Coleoptile
Epicotyl
Radicle
Hypocotyl
Endosperm
Pericarp fusedwith seed coat
Coleorhiza
Scutellum(cotyledon)
Seeds
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Fruits 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. usually a color change from green to another color organic acids and starch increase in concentration
sweet or tart fruit
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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.
Fruits
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As the fruit develops the outer wall of the ovary thickens and develops into the pericarpTissue that develops and surrounds a seedDevelops 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 peelMesocarp – or sarcocarp
Botanical term for the succulent and fleshy middle layer of the pericarp
Usually the part of the fruit that is eatenEndocarp – hard inner layer of the pericarp of
some fruits that contains the seed
Fruits
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Types of fruits Several types of fruits depending on their
developmental origin1. Simple: derived from a single carpel or several
fused carpels within one pistilCan be either fleshy or dryThe dry fruits can either be dehiscent (opening to
discharge seeds) or indehiscent (not opening to discharge seeds)
If the pericarp is fleshy – fruit is known as a simple fleshy fruit
e.g. apple, peach, pea, wheat, coconut, carrot, radish, tomato.
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
eachThe fruit is frequently called a “druplet” (raspberry) or
a bramble (blackberry).
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Types of fruits
Stamen
Stigma
Ovary
Pea flowerOvule
Seed
Pea fruitSimple fruit
Stamen
Stigma
Ovary
Raspberry flower
Aggregate fruit
Stamen
Carpels
Carpel(fruitlet)
Raspberry fruit
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3. Multiple – develops from an influorescence (a group of flowers tightly clustered together) – the walls of the ovaries thicken and fuse together e.g. pineapple, mulberry,
breadfruit There are fruits in which
structures other than the ovary contribute to the formation of the fruit These fruits are called
accessory fruits or false fruits
Types of fruits
Pineapple inflorescence
Multiple fruit
Flower
Eachsegmentdevelopsfrom the
carpelof oneflower
Pineapple fruit
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Seedless fruits Seedlessness is an important
feature of fruit crops like bananas, pineapples, grapes, watermelons, some citrus fruits (navel oranges, tangerines).
In some species, seedlessness is the result of parthenocarpy: Fruits set without fertilizationMay or may not require
pollination 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
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Seed Germination 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. Extended exposure to cold. Lettuce – requires increased light.
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Germination depends on the physical process called imbibitions.uptake of water due to the lower water potential of
the dry seedcauses the seed to expand and rupture its coatalso triggers metabolic events in the embryo that
enables it resume its developmentas 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
Seed Germination
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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.
Seed Germination
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Seed GerminationFoliage leaves
Cotyledon
Cotyledon
Hypocotyl
Hypocotyl
Radicle
Seed coat
Hypocotyl
Cotyledon
Epicotyl
Common garden beanNM Spirit
The End
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