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Today: Plant ReproductionW: Genetic Engineering of Plants

Fig 29.7

Seeds and pollen allow seed plants to reproduce without water

Fig 30.2

Animal pollinators move pollen from one plant to another

Fig 38.4

Plants reproduce, reward animals with sugar

Fig 38.4

a typical flower

Fig 38.2

Angiosperm Life Cycle

Fig 38.2

Fig 38.5

N

N

N

Each pollen grain has 3 nuclei, two sperm and one for the

pollen tube

Fig 38.5

NN

N

Each pollen grain has 3 nuclei, two sperm and one for the pollen tube

sperm

tube nuclei

Pollen tubes can grow quite long…corn stigma

corn seeds

Fig 38.5

The pollen tube grows to the egg and the sperm fuse with the egg= zygote and polar nuclei= endosperm

Fig 38.7

The zygote then develops into an embryo surrounded by the endosperm and seed coat

= the seed

Fig 38.8

The seed must contain enough nutrients to nourish the embryo until it can begin photosynthesis

Seed size is a good indicator of how much energy is stored to support early seedling growth.

Which seed likely requires light to germinate?

Fig 38.11

Seed dispersal can be by wind or often also by animal

Fig 38.10

Fruits:

Animals can get nutrients to disperse seeds

Fig 38.9Seed Germination...

Capsaicin is a deterrent to seed eating mammals

Capsaicin is a deterrent to seed eating mammals

Is this plant reproducing sexually?

Problem of Inbreeding•Close relatives have a higher probability of carrying the same genetic defects

•Decreases genetic diversity

see pg 813 and/or http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SelfIncompatibilty.html

How do plants avoid inbreeding?Some plants, like humans, separate the sexes--i.e., some plants have only male flowers and others only female flowers.

male plant

female plantFig 38.13

Fig38.13

Some plants physically separate the anthers and stigmas

Some plants separate the anthers and stigmas

How do plants avoid inbreeding?• Some plants, like humans, separate the

sexes--i.e., some plants have only male flowers and others only female flowers.

• Some plants separate the anthers and stigmas.

• Some plants have a cellular mechanism for avoiding inbreeding: self-incompatibility

see pg 813

What is self-incompatibility?• Plants, like animals have the ability to

distinguish self tissue from non-self tissue.

• In humans, generally non-self tissue is rejected, so tissue transplants can be a problem.

• In some plants self-pollen is rejected(= self-incompatibility), and only non-self pollen is allowed to fertilize the eggs.

see pg 813

Avoiding InbreedingSporophytic Self-incompatibility:

Stop Germination of Self Pollen on Stigma

Found in the Brassica family: mustard, turnips, broccoli…

see pg 813

Some signaling steps are known

• This SI method requires that a factor from the pollen recognizes a factor from the stigma

see pg 813

For sporophytic SI, male factors are made by the parent plant and placed in developing pollen

see pg 813

In sporophytic SI the reaction happens on the stigma surface

• If the male factor from pollen is recognized as self by the female factor on the stigma surface, then this recognition induces the stigma to secrete a substance that prevents the pollen from germinating.

• the substance secreted by the stigma that inhibits self-pollen from germinating is unknown.

see pg 813

Only pollen from different plants can germinate

see pg 813

Avoiding Inbreeding:Gametophytic Self-incompatibilityStop Pollen Tube Growth in Style

stigma

styleFound in the Solanaceae family: tomato, chili, tobacco…

see pg 813

Avoiding Inbreeding: Gametophytic SIStop Pollen Tube Growth in Style

• To reach the egg, the pollen tube must grow through the transmitting tract of the style, which secretes an enzyme called ribonuclease (RNase)

see pg 813

Avoiding Inbreeding: Solution #2Stop Pollen Tube Growth in Style

• The RNase enters pollen tubes of both self and non-self pollen.

see pg 813

Avoiding Inbreeding: Solution #2Stop Pollen Tube Growth in Style

• The RNase is inhibited in non-self pollen, but destroys the RNA in self pollen, and thus stops its growth toward the egg.

see pg 813

Self-incompatibility• Self-incompatibility (SI) is a method by

which some plants avoid inbreeding• The two main mechanisms of SI are different

from one another: one stops the pollen on the surface, the other stops the pollen in the style.

• Both methods require that a factor from the pollen recognize a female factor made by the flower, and in both methods this recognition initiates the SI reaction.

see pg 813

Fig 38.2

Angiosperm Life Cycle

Evolution does not always go “forward”…Some angiosperms disperse pollen by wind

Fig38.4

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Today: Plant ReproductionW: Genetic Engineering of Plants