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Overview
• Sexual VS asexual reproduction.
• Growth of a seed and fruit• Since agriculture started,
breeders have genetically manipulated traits of some wild crops by artificial selection.
• Now the speed and extent of plant modification have increased in recent decades with Genetic Engineering.
Flower Structure• Four modified leaves called floral
organs:– Sepals
• Enclose and protect the floral bud before it opens.
– Stamens• Reproductive organ.• Stalk and anther.
– Carpel• May have one or more carpels.• Ovary at the base
– One or more ovules inside.
• Long slender neck called the style.
– At the top there is a sticky structure called stigma.
» Landing platform for pollen.
Pollination Enables Gametes to Come Together Within a Flower
• Angiosperm sporophytes have a flower, a reproductive structure.
• Pollination brings a male gametophyte to the stigma of a flower.
• Germination brings a sperm from the gametophyte to a female gametophyte.– Located in the ovule,
embedded in the ovary of the flower.
• Fertilization happens within each ovule.
Gametophyte Development and Pollination
• Male gametophytes form in the pollen sac.
• Female gametophytes forms in each ovule.
• Pollination is transferring pollen from an anther to a stigma.
• A pollen grain makes it way down to the ovary.– Discharges sperm to a embryo
sac.– An embryo develops.
• The ovule develops into a seed.
– The ovary develops into a fruit which contains one or more seeds..
• When the conditions are ready they develop into seedlings.
Preventing Self-Fertilization
• Sexual reproduction has many advantages.– Genetic Diversity.– Better chance of some
offspring surviving a challenge.
• Self-Incompatibility– A plant rejects it’s own
pollen by not growing the pollen tube.
– Gametophytic self-incompatibility.
– Sporophytic self-incompatibility.
After Fertilization• Double Fertilization
– One sperm makes a zygote.– The other sperm make a triploid
nucleus called an endosperm.• Food storing tissue of the
seed.• Ovules turn into seeds.• Ovaries turn into fruit.
– Protect seeds.– Aids in dispersal.
• Types of fruit– Simple – From a single carpel or
fused carpel's.– Aggregate – A single flower with
more than one separate carpel forming fruits.
• All clustered together.– Multiple- A group of flowers
clustered together. When the ovary’s grows they all fuse together to form one fruit.
Seed germination• Dormancy
– As it matures it enters a phase of low metabolic rate.
– Waiting for the right condition to germinate
• The right conditions– Many species differ, some
example:• A lot of rain (Desert)• Forest fire (Competing plants
are gone)• The right season (Ensuring a
long growth season)• Light (Lettuce)• Weakened by chemicals
(Animals digestive tract)– Some seeds can remain dormant
for days to decades, some even longer.
Seed to Seedling• Begin by a process called Imbibition
– Uptake of water from the low water potential of the dry seed.
• The first organ to emerge form the seed is the radicle
– Embryonic root.• Then there are two ways for the shoot tip to
break through the soil surface.– First Way
• A hook shape forms from the hypocotyl.
• Growth pushes the hook above the surface.
• Light stimulates it to straighten.• Leaves emerge and start making
food from photosynthesis– Second Way
• The coleoptile, pushes upwards through the soil and into the air.
• The shoot tip grows through the tubular coleoptile. Breaking though the tip.
Asexual Reproduction• Exact clone of the parent• Advantages
– If it is in a stable environment then all of it’s offspring will be suited for that environment.
– Offspring aren’t as frail.• Usually mature vegetative
fragment from the parent plants.
• Disadvantages– An unstable enviroment
• New pathogens• Varied offspring means some
can survive.– If a catastrophic event
happened like a new disease, then all of them would die.
Mechanisms• Plants are able to renew or sustain
growth indefinitely.• Parenchyma cells can divide and
differentiate into more specialized types of cells.– A stem can get cut off and it
will grow roots and become a whole plant.
• Fragmentation– Separation of a parent plants
into parts the develop whole new plants.
• Apomixis– Producing seeds without
pollination.– No joining of sperm and egg.
• A diploid cell in the ovule gives rise to an embryo.
Vegetative Propagation and Agriculture
• Propagation is a form of asexual reproduction which plants grow new roots.
• Cutting– Cutting of parts of a plant that will grow
adventitious roots and form a whole new plant.
– A callus forms first and then the roots grow from that.
• If a node is included in the fragment then the callus stage is skipped.
• Grafting– A twig or bud from one plant can be grafted
onto a plant of a closely related species.• Combines the best qualities of each
– The plant that provides the root system is the Stock.
– The grafted part of the other plant is called the Scion.
• Test Tube Cloning– Able to grow whole plants by culturing smalls
pieces of tissue or even single parenchyma cells.
– Callus's form and hormones are used to shoot out roots.
– Then transferred to soil.– Can make transgenic plants by inserting
foreign genes.
Plant Biotechnology Transforming Agriculture
• Two meanings:– Innovations in the use of plants, or the
substances made by plants, to make products for humans.
– Genetically modifying plants in agriculture and industry