Angiosperm Reproduction and Biotechnology

Dillin Snape

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

Artificial Selection