BIOL 410 - Gymnosperms

What makes the gymnosperms significant?

• first to evolve seeds & pollen - profound evolutionary consequences in plant history

• it freed plants from needing water to carry spores, sperm, and egg = internal fertilization

• gymnosperms can live almost anywhere on the planet

What are the derived traits of gymnosperms?

• make pollen

• make naked seeds (seeds sitting on cone scales)

• internal fertilization

How did gymnosperms arise?

Data indicates that the SVPs evolved into the Progymnosperms, which evolved into the Gymnosperms upon seed evolution.

What is a fossilized example of a progymnosperm?

Archaeopteris.

What do archaeopteris resemble?

Resembles Pines and Redwoods. They have lage megaphylls. Also, they are the ancestor of gymnosperms.

Why are progymnosperms not gymnosperms yet?

They have spores only - no seeds.

What are some synapomorphies in archaeopteris?

• heterospory, gets passed onto the gymnosperms

• softwood - tracheids only

• bifacial cambium - 2º xylem and 2º phloem (minimal)

What is the oldest known seed plant?

Elkinsia. Integuments are incomplete.

What are ancestral traits in gymnosperms?

• heterospory

• 2º xylem and 2º phloem

• megaphylls

  They evolved first as synapomorphies in progymnosperms, then got passed into gymnosperms.

What are some derived (new) traits of gymnosperms?

• seeds

• pollen

• internal fertilization

true or false: progymnosperms and early gymnosperms arose in the Carboniferous era.

true

What happened at the end of the Carboniferous era?

• planet became cool/arid

• SVPs croaked because water was receding - external fertilization

• gymnosperms spread - internal fertilization

What are examples of phylum coniferophyta?

Redwoods, Pines, Firs, Spruces, Cedars. Only softwoods, so they had only tracheids.

What kind of needles did coniferophyta have?

Scale/needle-like leaves.

Why are most conifers monoecious?

The male and female are on the same plant.

What is significant about Junipers?

Conifers used to flavor gin. They have fleshy cone scales.

What is significant about the Yew Tree?

makes the drug taxol (anti-cancer). Inner bark treats breast cancer 4th stage and others. Now it is synthesized.

What is phylum cycadophyta?

Conifers that have the largest cones in the world. Pinnate leaves.

Why are cycadophyta dioecious?

Separate male and female plants to promote outcrossing. Males from one plant will fertilize females from another plant. This increases genetic variation.

Where are cycadophyta native to?

Tropics - no US species

What is phylum Ginkgophyta?

Dioecious conifer. No cone - seed coat is fleshy. Cleft leaves.

What do female seeds in ginkgophyta have?

Butyric acid - they smell very bad.

What does sex conversion mean in terms of ginkgophyta? and why?

Some branches of male trees become female. Evolved from monoecious ancestor.

What are the two plants in phylum gnetophyta?

Ephedra and Welwitschia.

What is ephedra? (Mormon Tea)

It is a shrub and has reduced leaves to prevent dehydration. Has XVMs and fibers. It also has double fertilization. Lives in arid environments and the desert. They are dioecious (male and female cones).

What is welwitschia?

A plant in the phylum gnetophyta. Has large, woody stem close to the ground. Has 2 large, meristematic leaves that split into segments. Dioecious (female and male cone).

Where is welwitschia native to?

Namibia/Angola-Southern Africa

true or false: pines have a sporic life cycle

true

Are pines heterosporous?

Yes. Microspores are on male cones. Megaspores are on female cones.

Why do we not notice male cones?

They release sperm and fall off.

What is pollen made in?

Male cone called a staminate strobilus.

Male cones develop out of the branches by what?

Mitosis.

What are the scales of the male cone called?

Modified leaves called microsporophylls.

What is attached to each microsporophyll (cone scale)?

Two microsporangia (pollen sacs).

What forms inside the microsporangia?

Microgametophytes (pollen grains with wings) form.

Why is all of the cone tissue 2N?

The cone forms by mitosis from the tree (a 2N sporophyte)

2N Microsporocytes go through what process to make 1N microspores?

Meiosis.

1N Microspores go through what to make 4 celled microgametophyte (pollen grain)?

Mitosis.

What are the 4 cells in the microgametophyte (pollen grain)?

• tube cell

• generative cell

• 2 prothallial cells (degenerating)

Why is the generative cell inside the tube cell?

The generative cell becomes sperm and the tube cell will deliver that sperm.

Why is the pollen grain an “immature” microgametophyte?

It has not formed sperm yet.

What happens once the pollen grains are made inside the male cone?

Pollen grains go from the male cone to the female cone. The male cones fall off/die.

What does the tube cell become once pollen grains germinate on the female cone?

Pollen tube.

Where does the generative cell stay?

Near the pollen tube tip as it grows.

What does the generative cell divide into?

2 non flagellated sperm. The sperm are not in water anymore, they will be delivered by the tube cell.

Why is non flagellated sperm a huge evolutionary advance over SVPs and Progymnosperms?

Allows Gymnosperms to live away from H2O and in arid environments.

What are some derived (new) traits that come with internal fertilization?

• pollen grain

• tube cells/pollen tube

• generative cell

• non flagellated sperm

Where does the pollen tube deliver the sperm?

To the female cone.

How long does it take for young cones (tiny and fleshy) to develop into mature female woody cones?

1-2 years.

How many seeds are on each cone scale?

2 seeds.

1 integument + 1 megasporangium =

1 ovule (immature seed)

Why is an ovule called an immature seed?

It does not have an embryo yet in it.

When do young fleshy cones form on tree by mitosis?

January every year.

Why are the integuments of the cone scales open?

The opening (micropyle) receives pollen.

When pollination is complete, what does the ovule secrete?

A sugar droplet for the pollen grain to germinate in. The integuments close, so the seed is closed up after pollination is complete. The pollen grain is trapped in there.

What starts the formation of the female gametophyte?

Pollen tube releases enzymes.

Why does pollen tube growth stop?

Waits for female gametophyte to develop an egg. The pollen tube has sperm but does not want to deliver it unless there’s an egg present.

How many megaspores are formed through meiosis of megasporocytes?

4

3 megaspores degenerate. The 1 megaspore left develops into the gametophyte. Why?

1 big spore left to make 1 big gametophyte. That is specific to internal fertilization.

What happens to the 1 remaining megaspore?

It goes through mitosis to make the female gametophyte (archegonia & eggs). Now the stage is set for fertilization because the female gametophyte is mature.

The cone increases in size. Why?

There is a female gametophyte inside with an egg, ready to be fertilized.

What causes the pollen tube to re-initiate growth?

The eggs/mature gametophyte release enzymes.

What happens to the two non flagellated sperm produced by the generative cell?

1 sperm is fertilizing the egg nucleus, and the other one is going to degenerate.

What does the fertilized egg develop into?

Zygote, which then develops into the Embryo via mitosis.

What does the embryo grow in?

Grows in the female gametophyte, which will be the food for the developing embryos.

What happens to the cones once the embryo matures?

Integuments harden into seed coat. Cones open and drop seeds to grow new plants. Mature cones have woody scales.

What is the ploidy of the coat and megasporangium?

2N

What is the ploidy of the female gametophyte?

1N

true or false: embryos are always diploid (2N).

true

Why are female cone scales modified branches?

They have modified leaves (bracts) below them. Cone scales evolved from branches (above) and bracts from leaves (below).

Why are the scales of a male cone much smaller than the scales of a female cone?

They don’t hold eggs, just sperm for dispersal.

Why are male cones on the ends of branch tips?

Better dispersal.

The entire cone begins at what ploidy level?

2N because the tree goes through mitosis to make the cone, and the tree is 2N.

Describe how 2N microsporocytes inside of the microsporangia become pollen grains.

2N microsporocytes go through meiosis to make 1N microspores, which go through mitosis to form the gametophyte.

What is the function pf the megasporocyte?

To develop into megaspores.

Why is the mechanism of the pollen tube releasing enzymes to trigger the development of the ovute into the female gametophyte of adaptive value?

Better reproduction value, allows sperm & egg to develop together.

In a new female cone, the ovules inside contain what?

Integuments, megasporangium, and megasporocytes (2N).

In an older female cone, the ovules inside contain what?

Integuments, megasporangium, and megaspores (1N).

Once the megagametophyte is mature, the stage is now set for what?

Fertilization.

Describe the fertilization process.

Egg releases enzymes to re-initiate pollen tube growth. The pollen tube digests through the megasporangium, then starts fertilization.

What were the two scars on each scale in the mature ovulate cone?

seeds.

The closed cone Torrey Pine needs what to open?

Fire.

The Giant Redwood cones need what to open?

Fire or Animals.

What are the benefits of fire to an ecosystem?

• seed germination

• ash (nutrients) for new plants

• stimulates plants to sprout new branches

• kills competing grasses that take nutrients

• kills excess insects

Explain the benefits of control burns for us and plants.

• prevents fuel build up

• decreases competition in shade

• germinates seeds

• decrease pathogens

• ash puts nutrients in soil

The largest Pine Cone in the world is?

Cycads.

How would you identify a Cycad?

Pinnate, produces cones.

How can you tell Cycads and Palms apart?

Palms are flowering plants.

Which has more derived traits, Cycads or Palms? Why?

Palms. They are flowering plants, therefore they have more derived traits.

The Phylum Ginkgophyta was once very diverse. Now, how many species exist today?

Only 1 species.

What saved the ginkgophyta from going extinct?

It was cultivated by priests in the temple gardens of ancient China and Japan. Today it is planted all over.

Describe the structure of welwitschia.

2 large meristematic leaves that split.

Name 3 traits that are in pine needles due to arid adaptations.

• thick cuticle

• folded parenchyma

• needle shaped

How can you tell that the vasculature in pine needles are megaphylls?

2 veins on the leaf.