Chapter 38: Angiosperm Reproduction
& Biotechnology
Plants
reproduce both sexually & asexually
In angiosperms
Sporophyte
is the dominant generation
Sporophyte reproductive flowers
Gametophyte is dependant upon sporophyte
Male
gametophyte anthers
Female gametophyte ovule
Fertilization occurs within ovule of ovary
ovule
becomes seed
ovary becomes fruit
Floral Structure
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Determinate shoots attached to stem at
receptacle
4 whorls
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Stamens & carpels= reproductive organs
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Stamen (male)
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Carpel (female)
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Filament=stalk
Anther=terminus to filament in which pollen is located
Pistil=single or fused carpel
Ovary at base
Style= slender neck of carpel
stigma= sticky top of style for capturing pollen
Ovules located within ovary
Sepals & petals = sterile
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Sepal- protect flower organs
Petals- attract pollinators
Gamete development & pollination
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Male
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Pollen sacs (microsporangia)
contain microsporocytes (2n) that form
microspores (n)
Any microspore can become a male
gametophyte
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Microspore divides by mitosis generative cell & a
tube cell
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Pollen grain=generative cell + tube cell + spore wall
Maturation of generative cell occurs within the tube cell
Tube cell will form pollen tube
Generative cell divides to form 2 sperm cells
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Female
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Megasporangium in ovary of ovule
Megasporocyte (2n) divides to form
megaspores (n)
In most angiosperms:
1 of 4 megaspores survives
 Surviving megaspore divides without cytokinesis to
form a large cell with 8 haploid nuclei
 Large cell partitioned in gametophyte embryo
sac
 Embryo sac has 3 cells at one end
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1 egg
2 synergids (attract/guide pollen tube)
Rest of embryo sac= 3 antipodal cells & 2 polar nuclei
Pollination
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Transfer of pollen from anther to stigma
Accomplished by:
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wind
H2O
Insects
bird or animal transfer
Preventing self-fertilization in Dioecious species
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Stamens & carpels
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Mature at different times
Arranged to prevent selfing
Self-incompatibility
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Plant rejects pollen of closely related species
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biochemical or pollen tube formation block
Based on ability to recognize self from non-self
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Results from S genes
Double fertilization
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1 sperm fertilizes egg= zygote
Other sperm combines with 2 polar nuclei
to from triploid (3n)=endosperm
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Endosperm= food storing tissue of seed
Endosperm develops only in ovules with a
fertilized eggconserves nutrients
After double fertilization
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Ovule=seed
Ovary=fruit
Endosperm function often taken over by
swelling cotyledons of the fruit
Embryo development
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Zygote divides to form
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Basal cell
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Form suspensor anchors embryo to parent
Terminal cell
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Gives rise to most of embryo
Divides to form proembryo cotyledons
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Shoot apical meristem located in shoot apex between
cotyledons
Opposite shoot apex=root apex with the root apical meristem
Mature seed structure
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Last stages of development
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Seed dehydrates
Seed coat forms from integuments of ovule
Embryo becomes dormant & enclosed within the seed coat
Ovary to fruit
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While seeds develop from ovules flowers
develop into fruit to protect seeds & aid in their
dispersal
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Caused by hormonal changes triggered by fertilization
Ovary wall=pericarp (thickened wall of fruit)
Seed germination
Dormancy of seed must be broken by favorable
conditions &/or environmental cues
Seed to seedling
 Germination dependant on imbibition
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Seed expands & ruptures its coat
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Triggers metabolic changes
Radicle
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Uptake of H2O due to low Y of dry seed
Embryonic root
First to emerge
Shoot
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Hypocotyl hook forms to break soil surface
Light causes hypocotyl hook to straighten
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Raises cotyledons & epicotyl
epicotyl forms leaves
Cotyledons shrivel & fall away
Monocots- coleoptile pushes up through soil; shoot tip grows
from coleoptile
Asexual reproduction in plants
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Large amount of seeds are produced
sexually to compensate for those lost to
herbivores & environmental hazardscostly energetically; Some species choose
asexual reproduction as a result of that
cost
Asexual reproduction=vegetative
reproduction
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Offspring are usually mature, vegetative
fragments of parent distributed locally
Offspring at higher risk of local extinction if
catastrophic event of new parasite occurs
Mechanisms for asexual
reproduction
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Fragmentation
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Apomoxis
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Shoot or stem cutting with callus (mass of dividing cells)
develops adventitious roots or nodes that develop into whole
plant
Grafting
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Seeds produced without pollination or fertilization
Diploid cell in the ovule gives rise to embryo & mature seeds
Clones from cuttings
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Separation of parent plant into parts that develop into whole
plants
Young twig or bud grafted onto a closely related species
Combines qualities of both plants
Stock=plant that contributes root system
Scion= twig grafted onto stock
In vitro cloning of plants
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Make multiple copies
Use for production of Genetically Modified Organisms (GMO)
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Foreign gene inserted into plant genome; plant expresses foreign
gene
Plant Biotechnology, Agriculture, &
the consequences
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Artificial selection
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Manipulating reproduction & genetic make-up
of plants for human benefit
Biotechnology
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Used to insert genes into crops which
Increase crop yields through pest resistance
 Increase nutritional value of crops
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Consequences of GMOs
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Increase in food allergies
Adverse effects on non-target organisms
Possible “superweeds”