Lecture (3)

Plant growth & developmentPlant growth & development

Dr/ Bardees Mohammad Ahmad MickkyDr/ Bardees Mohammad Ahmad Mickky

Lecturer of Plant Physiology

Botany Department, Faculty of Science

Mansoura University

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IntroductionIntroduction

Metabolism - Growth - Development

GrowthGrowth

Definition of Growth

Growth Curve

Types of Growth

Phases of Growth

DevelopmentDevelopment

Definition of Development

Differentiation - De-differentiation - Re-differentiation

Developmental Transition in Plants2

Main topics in lecture (3):Main topics in lecture (3):

Metabolism was previously defined as

a summary of all biochemical reactions

occurring within a living cell

or

a summary of all biological reactions

occurring within a living organism

We have also learned that metabolic processes may be

anabolic, i.e. synthetic activities with a net build up

catabolic, i.e. degrading activities with a net break down

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Metabolism Metabolism -- Growth Growth -- DevelopmentDevelopment

Anabolic and catabolic activities are

not only the reverse of each other,

but they are also interlinked

(e.g., photosynthesis & respiration)

Moreover, anabolic and catabolic activities

occur in a programmed fashion under definite control

with a certain balance according to the cell demand

Under normal conditions and before senescence,

anabolism should occur in excess of catabolism;

and when this occurs, growth results

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So, growth is an outcome of metabolism

More precisely, what is the philosophy of metabolism?

in other words,

why do biochemical reactions occur within the living cell?

or,

why do biological reactions occur within the living organism?

The answer is simply; to keep it alive

And it here refers to the cell and subsequently to the organism

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But definitely the cell or the organism will not be still alive forever,

it will live for a time that we scientifically call the life cycle

During the life cycle, the organism should NOT remain as the same

with the similar shape, form, structure,

mass, size weight or number of cells.

Instead, certain changes will occur;

and such changes should be positive in both

quantitative (increase) and qualitative (enhancement) levels

So, growth and development are the outcomes of metabolism

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Growth is a gradual permanent irreversible

increase in the plant dry weight

due to the increase in both:

cell number via cell division

and

cell size via cell enlargement.

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Definition of GrowthDefinition of Growth

Growth curve is an S-shaped or sigmoid curve

obtained when we plot growth against time.

This curve mainly shows 4 phases of growth:-

1- initial slow growth (lag phase)

2- rapid period of growth (log / exponential phase)

3- another slow period (diminishing phase)

4- finally growth stops (stationary / steady phase).8

Growth CurveGrowth Curve

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(1) Primary and secondary growth:

The increase in plant length due to the activity of

apical meristems (shoot & root tips)

is a vertical type of growth known as primary growth.

The increase in plant diameter due to the activity of secondary

meristems (lateral & intercalary meristems) is a horizontal type

of growth known as secondary growth.

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Types of GrowthTypes of Growth

(2) Limited and unlimited growth:

Plant stem and root usually grow continuously

from early germination stages to plant death.

This type of growth is called unlimited or indeterminate growth.

However, leaves, flowers and fruits

stop growing after attaining certain size.

This type of growth is called limited or determinate growth.

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(3) Vegetative and reproductive growth:

The earlier growth of plant producing

leaves, stems and branches without flowers

is called vegetative growth.

After the vegetative phase of plant growth, plant produces

flowers which are the reproductive part of the plant.

This is called reproductive growth.

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(4) Annual, biennial and perennial growth:

Annual plants complete their life cycle from germination through

flowering and seed production to death in a single year or less.

e.g., cereals and legumes.

Biennial plants complete their life cycle in two years.

e.g., onion and carrot.

Perennial plants live many years, and often die not from old age

but from an infection or some environmental trauma.

e.g., shrubs and trees.13

The period of growth can be generally divided into 3 phases:

1- Phase of cell division (Formation phase)

2- Phase of cell enlargement (Elongation phase)

3- Phase of cell differentiation (Maturation phase)

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Phases of growthPhases of growth

11-- Formation phaseFormation phase

The meristematic cells of shoot and root apex

divide repeatedly and rapidly

to add new cells to plant length.

These cells are characterized by:dense protoplasm

large nucleus

thin primary cell wall

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22-- Elongation phaseElongation phaseThe new cells formed through cell division

begin to increase in size due to:increased vacuolation (vacuole increase in size)

cell wall growth (new deposition + stretching)

33-- Maturation phaseMaturation phaseThe cells assume certain forms

based on their function to form the various plant tissues.

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Thus, there are 3 main activities involved in

plant growth and development:

1- Cell division

2- Cell enlargement

3- Cell differentiation

division and enlargementresults primarily from both cell Growth

while development occurs as the sum of

growth and differentiation

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Definition of DevelopmentDefinition of Development

Differentiation is a process during which

cells undergo structural changes

in their cell wall and protoplasm

to possess distinct morphology

with unique function.

.A differentiated cell can not divide

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Differentiation Differentiation -- DeDe--differentiation differentiation -- ReRe--differentiationdifferentiation

However, an undividable differentiated cell sometimes

regains the power of division in a process known as

de-differentiation. Now, a de-differentiated cell

can divide to produce new cells.

Again, these newly-produced cells loose the ability to divide

and become a part of permanent tissue. This process is

called re-differentiation.

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Plants undergo several developmental transitions

during their life cycle.

Shoot of higher plants passes through 3 more or less distinct

phases during its post-embryonic development, and these are:1- Juvenile vegetative phase,

where the plant is not competent to flower

2- Adult vegetative phase,

where the plant can respond to floral inductive signals

3- Reproductive phase,

where the flower is produced to undergo reproduction

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Developmental Transition in PlantsDevelopmental Transition in Plants

Lecture (4)

Plant growth & developmentPlant growth & development

Dr/ Bardees Mohammad Ahmad MickkyDr/ Bardees Mohammad Ahmad Mickky

Lecturer of Plant Physiology

Botany Department, Faculty of Science

Mansoura University

1

Vegetative GrowthVegetative Growth

Leaf Growth

Phytohormonal Levels during Leaf Growth

Environmental Effects

Reproductive Growth Reproductive Growth

Flowering

Pollination

Fertilization

Seed Formation & Fruiting

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Main topics in lecture (4):Main topics in lecture (4):

Leaf growth occurs due to the growth of both:

lamina and petiole

This occurs due to the increase in

cell number via cell division

and

cell size via cell expansion.

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Leaf GrowthLeaf Growth

4

Phytohormonal Levels during Leaf Growth Phytohormonal Levels during Leaf Growth

Phytohormones

Growth Activators Growth Inhibitors

Auxins

Cytokinins

Gibberellins

ABA

Ethylene

Jasmonate & related

High Levels

During

Leaf Growth

High Levels

During

Leaf Growth

Leaf growth is affected by different environmental factors

such as:

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Environmental EffectsEnvironmental Effects

Temperature

Light

Water

Minerals

Pests & Diseases

Reproductive growth begins with the formation of flower

in a process known as flowering.

Flowering is highly affected by:

1- Light

( photoperiodism: response to light / dark ratio = day / night ratio)

2- Temperature

(vernalization: need for cold temperature)

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FloweringFlowering

Photoperiodism is the response of plants to

day/night or light/dark ratio.

The response of plants to day/night ratio may be:

seed germination, vegetative growth or flowering.

Flowering is the first photoperiodic response to be discovered

and the most studied response.

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Some plant species need low day/night ratio to flower,

so they bloom in winter and are called

short day plants (e.g., soybean).

Other plant species need high day/night ratio to flower,

so they bloom in summer and are called

long day plants (e.g., spinach).

The last type of plant species flower

regardless of day/night ratio,

and they are called day neutral plants (e.g., tomato).

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Vernalization is the artificial exposure of

plants (or seeds) to low temperatures

in order to stimulate flowering.

For example; winter wheat would not flower

without a period of chilling (vernalization).

Pollination is the transfer of the male pollen grain from flower

stamen to the female ovule in the flower carpel.

This transfer process may happen with the aid of:

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PollinationPollination

Wind

Insects

Animals

Human

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””Flower PartsFlower Parts““

Flowers may have

only male or female organs (called imperfect flowers)

or both together (called perfect flowers).

These terms should not be confused with

those that describe the plant as whole.

The individual plant may produce

either male or female flowers (called dioecious plant )

or produce both (called monoecious plant ).

In monoecious species,

individual plant may have imperfect or perfect flowers.

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Only after pollination,

when the pollen has landed on the stigma of a suitable flower,

the pollen grain on the stigma grows a tiny tube,

all the way down the style to the ovary.

This pollen tube carries a male gamete

to meet a female gamete in an ovule.

In a process called fertilization,

the two gametes join and their chromosomes combine,

to form a fertilized ovule called a zygote.

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FertilizationFertilization

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Seed Formation & FruitingSeed Formation & Fruiting

The fertilized ovule goes on to form a seed,

which contains a food store and an embryo.

The ovary develops into a fruit to protect the seed.

That embryo will later grow into a new plant

after the processes of

germination, growth and development.

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