Chap 1 Plant Development

8/10/2019 Chap 1 Plant Development

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DEVELOPMENTAL BIOLOGY


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INTRODUCTION 4 credits (3+1)

Plant

Test 1 (15%)

Quiz (5%)

Mini project (10%)

No lab


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INTRODUCTION

Plant development

Gametogenesis

Pollination and Fertilization Embriogenesis

Germination of embryo

Shoot development Root development

Flower and reproduction organ
http://www.flickr.com/photos/mr_moor/1074992334/


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PL NT DEVELOPMENT
http://www.flickr.com/photos/mr_moor/1074992334/http://www.flickr.com/photos/mr_moor/1074992334/


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Seed

Seedling

Mature plantsFlowering

Fruiting

Plant Life Cycle

(1) How is a seed formed?

(2) How does a seed

become a seedling?

(3) How is shoot formed?

(4) How is root formed?

(5) How is a flower

formed?


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Tissue System

and Its Functions

Component Tissues Location of Tissue Systems

Dermal Tissue System

protection

prevention of water loss

Epidermis

Periderm (in older stems

and roots)

Ground Tissue System

photosynthesis

food storage

regeneration

support

protection

Parenchyma tissue

Collenchyma tissue

Sclerenchyma tissue

Vascular Tissue System

transport of water and

minerals

transport of food

Xylem tissue

Phloem tissue


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The "Typical" Plant Body The Root System

Underground (usually)

Anchor the plant in the soil

Absorb water and nutrients

Conduct water and nutrients

Food Storage


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The Shoot System Above ground (usually)

Elevates the plant above the soil

Many functions including: photosynthesis

reproduction & dispersal

food and water conduction


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Plant development: the formation of a complete embryo from a zygote

seed germination

the elaboration of a mature vegetative plant from theembryo

the formation of flowers, fruits, and seeds;

plant's responses to its environment.

Plant development encompasses the growth anddifferentiation of cells, tissues, organs, and organsystems.


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Plant growth vs animal growth

Animalsexhibit a growth pattern called determinate growth.

After fertilization, the zygote cells are rapidly dividing,undifferentiated cells

However, after a certain critical stage, the cells differentiate andform tissues.

From this point onward, their developmental fate is sealed

There are exceptions to this (i.e. stem cells in bone marrow)

Most animals have a pre-programmed body plan (i.e. barringmutation or accident, most humans have 10 fingers and toes, twoeyes, a heart with four chambers, etc..)

Most animals quit growing after a certain age


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Plantsexhibit a growth pattern called indeterminate growth

The plant retains areas where rapidly dividing,undifferentiated cells remain all through the life of the plant

These areas are called meristems Meristematic tissue continues to rapidly divide producing

undifferentiated cells which may eventually differentiate to form thetissue and cell types

Plants do not have a pre-programmed body plan

There are constants like leaf shape and branching patters (opposite,alternate, etc.) but you can never predict where a new branch willcome about on a tree...

Plants continue to grow throughout their life


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Fertilization of a 1N (haploid) egg cell by a1N sperm nucleus.

regulation of the balance between cell growthand cell division help create the shape of theembryo,

formation of distinctive patterns of organs,

cells and tissues differentiation, Molecular mechanisms of determination

generate different cell types.

Plant and Animal development have in common:
http://biology.kenyon.edu/courses/biol114/Chap11/Chapter_11.htmlhttp://biology.kenyon.edu/courses/biol114/Chap11/Chapter_11.html


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Lateral meristem:

Located on the sides of roots or stems

supply cells for the plant to increase in girth

Secondary growth

found in all woody and some herbaceous

plants lateral meristems and secondary growth found

only in dicots

Vascular cambium, cork cambium

Intercalary meristems:

At the base of leaf primordia and above thenodes in stems

In monocots


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Plants have tremendous developmental plasticity.

Lost plant parts can be regenerated by meristems, and even entire plants canbe regenerated from single cells.

environmental factors such as light and temperature can greatly influenceoverall plant form.

Plant cells are totipotent; that is, able to differentiate as a different cell type if

given the appropriate stimulus. Totipotency is likely a reflection of the plant's sedentary lifestyle.

Plants can't escape predators and other kinds of damage, but they can readilyrepair wounds and reconnect vascular strands by differentiating theappropriate cell types

Plasticity: ability to change form or shape in response to a change inenvironment, no genetic change is involved

Cell-cell communication is important in plant development, but cellrecognition is likely less important than it is in animals since plant cellskeep the same neighbors throughout their life.


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Alternation of generation

ALL PLANTS have a Life Cycle that involves TWO PHASES.

THE FIRST PHASE: a haploid gametophyte that produces eggsand sperm.

THE SECOND PHASE :a diploid sporophyte that produces

spores. This type of life cycle, which alternates between the Gametophyte

Phase and the Sporophyte Phase, is called ALTERNATION OFGENERATIONS.

in nonvascular plants, the gametophyte is the dominant phase.

in vascular plants the sporophyte phase is the dominant phase. in seedless vascular plants, the gametophyte is usually a separate

small organism quite different from the sporophyte.

in seed plants, the gametophyte is a very small parasite of thesporophyte, the flower.


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gametophytes

are anchored into

soil by threadlike

protonemaand

single-celledrhizoids

sporophytes=

brown stalks

growing out ofthe female

gametophyte


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Bryophyte life cycle

1) spores can disperseby windwhy is dispersal important?

- allows colonization of new (maybe better) habitats

- allows escape for offspring if local conditions turn bad

- prevents inbreeding

2) sperm have to swimto reach eggthis requires environmental water

- limits where bryophytes can grow

- think about how this limited the ability of bryophytes to take

over the world of dry land, compared to plant groups that evolved later

- on the plus side: no need for pollinators, just rain or splashes

3) what features of the bryophyte body also limit:

- the size of these plants?

- the environment in which they can live?


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Common Characteristics

Motile sperm

Gametophyte thallus most prominent generation, notsporophyte

Thallus = plant tissue undifferentiated into a

leaf, stem or root

Most leaves lack cuticle

For absorption

No true leaves, stems or roots

All bryophytes: homosporous Produce 1 kind of spore

Spore develops into gametophyte

Gametophyte produces both antheridia (sperms) and archegonia(eggs)


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male and female reproductive structures

female

male


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Fern and fern allies

Possess xylem and phloem but do not

produce seeds

Share other common features withBryophytes

Sporophyte dominates the life cycle

Gametophytes are often microscopic and areindependent of sporophyte

Ferns are ancestors of modern seed plants


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Life cycle

Life cycle is similar to bryophytes

The diploid form is the dominant generation (larger,long-lived)

The haploid form is the lesser generation (smaller,short lived).

Egg in archegonia and sperms in antheridia

Zygote germinates and matures into diploidsporophyte

The sperms are motile and need water forfertilization

Sporophyte and gametophyte are independent

Sporophyte dominates the life cycle


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Stained sporophyte

growing fromgametophyte


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The seed plants

Seed plants are the most derived tracheophytes.

Gymnosperms (such as pines and cycads)four phyla

Angiosperms (flowering plants) one phyla

Big evolutionary innovations

1. Evolution of a seed

2. Reduction in gametophyte generation The haploid gametophyte is attached to and

nutritionally dependent on the diploid sporophyte.


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3. The seed plants are heterosporous

Separate megasporangia and microsporangia

Megaspores produce a single, haploid,multicellular female gametophyte inmegasporangia

4. Microspores meiotically divide to producepollen grains in microsporangia

5. Fertilization occurs through pollen tubeelongation to thefemale gametophyte

(ovules)which release two sperms Resulting zygote divides until an embryonic stage

is reached, when growth is halted (producing aseed).


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Advantages of reduced gametophytes

Protect the female gametophytes from

environmental stresses. Eg. Drying out, UV

Obtain nutrients from the sporopytes In contrast seedless plants must fend for

themselves


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SEED vs. SPORE

Advantages of seeds over spores (and seed plants

overspore-producing plants):

Multicellular layer of tissue (spores: single-celled)

Protective coat

Stored food supply

These advantages allowed these propagules to

remain dormant and survive in environmentalextremes, even fire, giving them a selective

advantage over spores and spore-bearing plants


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Gymnosperms life cycle


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The flowering plant

(angiosperm) life

cycle


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The flowering plant (angiosperm) life cycle


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Fertilization

The pollen grain is deposited on the stigma (this ispollination) and germinates to produce a pollen tube.

The pollen tube grows down through the style, this

growth is controlled by the tube nucleus. The pollen grain is able to penetrate the style

because of the secretion of digestive enzymes

The pollen tube enters the micropyle (by this time

the generative nucleus has undergone its mitoticdivision so there are two male nuclei [gametes]

present)


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Pollen grain


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eight-celled female gametophyte


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Germinating Pollen Grain from a Lily


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The male nuclei enter the embryo sac

one fuses with the egg cell to form a diploid zygote -

this will give rise to the embryo

the other fuses with the two polar nuclei to form a

triploid endosperm nucleus - this will give rise to the

endosperm that will nourish the developing embryo.

This process is known as a double fertilizationbecause two fusions occur.


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The egg celland polar nucleiare contained within theembryo sac.

The sperm nucleiare derived from the pollen grains


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One sperm nucleus fertilizes the egg, generating a 2Ndiploidzygote.

Another sperm nucleus fertilizes a polar cell with two 1Nnuclei, generating a 3N triploid endosperm, which providesnutrients to the developing embryo.

Double fertilization


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Plant embryogenesis begins with anasymmetric cell division, resulting in aapical(terminal) and basalcell.

Apical cellsmaller and denselycytoplasmic

Basal cell- larger and has a big vacoule

This first asymmetric division providespolarity to the embryo.

Most of the plant embryo develops fromthe apical (terminal) cell.

The suspensordevelops from the basalcell. The suspensor anchors the embryo tothe endosperm and serves as a nutrientconduit for the developing embryo.

Embryogenesis


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Division of the apical cell give rise to the embryo.

Developmental stages:

The first three divisions in the apical cell give rise to eight-celledproembryo.

Further cell division leads to the globularstage. The three basic tissue systems (dermal, ground, and vascular) can be recognized

at this point based on characteristic cell division patterns.

The globular shape of the embryo is then lost as the cotyledons (embryonicleaves) begin to form.

The formation of two cotyledons in dicots gives the embryo a heart-shapedappearance. In monocots, only a single cotyledon forms.

Upright cotyledons can give the embryo a torpedo shape

the suspensor is degenerating the shoot apical meristem and root apical meristem are established.

These meristems will give rise to the adult structures of the plant upongermination. Further growth of the cotyledons results in the torpedo andwalking-stick stages.

At this point, embryogenesis is arrested, and the mature seed dessicates andremains dormant until germination.


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the descendants of the apical cell are shown in yellow, and the descendants of the basal cell are shown in pink.


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Stages of growth and development of the embryo


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seed

A seed is an

embryo

surrounded by aprotective coat.


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Seeds in a Pod


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Seed germination

hypogeal

epigeal


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The root apex

Shoot apex

Leaf development Internodal elongation

Lateral bud initiation

Flowering apex Secondary growth

Senescence

The adult body

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Chap 1 Plant Development