Exam #2 F 2/29 in class Office Hours Th 2/28 from 10-11:30am and 1:30-2:30pm Review Th 2/28 5pm in PAI 3.02 Discussions- normal Th/F plus Th 9am in Bio 214

CB 29.7

Seeds and pollen allowed seed plants to reproduce without water

CB Animal pollinators move pollen from one plant to another

CB Plants reproduce, reward animals with sugar

CB 30.7 a typical flower

CB 38.2 Angiosperm Life Cycle

CB 38.4 N N N Each pollen grain has 3 nuclei, two sperm and one for the pollen tube

CB 38.4 N N 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

CB 38.6 The pollen tube grows to the egg and the sperm fuse with the egg= zygote and polar nuclei= endosperm

CB 38.7 The zygote then develops into an embryo surrounded by the endosperm and seed coat = the seed

CB 38.8 The seed must contain enough nutrients to nourish the embryo until it can begin photosynthesis

CB 30.9 Seed dispersal can be by wind or often also by animal

CB 30.8 Fruits: Animals can get nutrients to disperse seeds

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

Is this plant reproducing sexually?

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

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

CB 38.5 Some plants separate the anthers and stigmas

How do plants handle the problem? 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

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.

Avoiding Inbreeding, Solution #1: Stop Germination of Self Pollen on Stigma Found in the Brassica family: mustard, turnips, broccoli…

Some signaling steps are known for solution #1 This SI method requires that a factor from the pollen recognizes a factor from the stigma

For solution #1 of SI, male factors are made by the parent plant and placed in developing pollen

In SI solution #1 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.

Avoiding Inbreeding: Solution #2 Stop Pollen Tube Growth in Style stigma style Found in the Solanaceae family: tomato, chili, tobacco…

Avoiding Inbreeding: Solution #2 Stop 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)

Avoiding Inbreeding: Solution #2 Stop Pollen Tube Growth in Style The RNase enters pollen tubes of both self and non-self pollen.

Avoiding Inbreeding: Solution #2 Stop 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.

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.

CB 38.2 Angiosperm Life Cycle

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

Exam #2 F 2/29 in class Office Hours Th 2/28 from 10-11:30am and 1:30-2:30pm Review Th 2/28 5pm in PAI 3.02 Discussions- normal Th/F plus Th 9am in Bio 214