STATE LEVEL TRAINING FOR DISCTRICT

RESOURCE GROUP

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XI Std. Bio-Botany & Botany – Vol. II

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Venue: Sri SaiRam College of Engineering, Chennai

Date: 30.11.18 & 01.12.18

STATE COUNCIL OF EDUCATIONAL RESEARCH AND TRAINING, CHENNAI – 06

PLANT GROWTH�AND �DEVELOPMENT

CHAPTER 15

Banyan tree

Paddy plant

What is Growth?

Growth is defined as an irreversibile

Perminant increase size,shape,volume and dry weight it also occurence cell division, cell elongation and differentiation.

Growth rate in plants

Bamboos :Fast growing plant (certain species 91 cm per day).

Saguaro cactus: slow growing plant (I inch in first 10 years).

Growth is measureable

In maize root : more than 17500 new cells produced per hour.

In water melon : increase in size up to 350000 times.

Water melon

Maize root

Characteristics of growth

Eq: stem,root

[Indeterminate]

Eq: Leaves,flowers.

[Determinate]

Vascular cambium and cork cambium

coconut

Annual plant – paddy

Perennial plant-bamboo

Phases of Growth:

1.Formative phase:

• by meristematic cells.
• mitotic cell division.

2.Elangation phase:

• deposition of new cell wall materials(intussusception).

3.Maturation phase:

• thickening and differentiation takes place.
• Cells do not grow further.

Kinetics of Growth

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Stages of growth:

Grand period of growth:(sigmoid curve)

• The total period from initial

to final stage of growth.

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Four phases

1. Lag phase:

• Initial stage of growth.
• new cells are formed from

pre-existing cells .

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Motion analysis of the of cells or expansion is called kinetics of growth.

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2.Log phase or exponential phase:

• growth rate is maximum.
• Rapid growth phase.
• Physiological processes are quite fast.

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3. Decelerating phase or slow growth phase:

• Rate of growth is decreases.
• Metabolic process becomes slow.

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4.Maturation phase:

• New particles deposition on inner surface wall.
• Growth rate becomes zero.

• The length of plant is plotted against time, it shows a linear curve and this growth is called arithmetic growth.

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• Rate of growth is constant.

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• One cell is continue to divide and other cells change to body cells.

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Linear Growth Curve

Arithmetic and geometric growth of embryo:

• Young embryonic plant grows geometrically (all cells divide).
• Later, cell division restricted at tips of roots and shoots it is an arithmetic type.

Absolute growth and relative growth

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Conditions of growth

External factors

• Water-need for cell growth and enzymatic activity.
• Nutrition-formation of protoplasm and source of energy.
• Temperature-28 C to 30 C for proper growth and above 45 C hinders the growth.
• Oxygen-necessary for respiration.
• Light-presence of light promote the growth absence of light is leads to etiolation.

Internal factors

Genes-intracellular factors.

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Phytohormones-intercellular factors.

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Carbohydrates and Nitrogen ratio.[C/N ratio]

• More nitrogen compounds produce vigorous vegetative growth.
• More carbohydrates favour for mechanical tissue.

Measurement of plant growth�Arc auxanometer

Sequences of developmental processes in a plant cell

1.Differentiation:

• meristematic tissue change to specific tissue and specific function.

2.Dedifferentiation:

• Living differentiated cells are regaining the ability of cell division. Example: vascular cambium.

3.Redifferentiation:

• Multiplication again lose the ability to divide: Secondary xylem

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Plasticity

• Plants follow different pathways in response to environment or phases of life to form different kind of structures. This ability is called plasticity.
• Heterophylly is an example of plasticity.
• Examples: cotton, coriander.

Plant growth Regulators[PGRs]�[chemical messenger]

Characteristics of phytohormones

• Usually produced in tips of roots and stems.
• Transfer of hormones from one place to another place.
• Require in trace quantities.
• Organic in nature.
• No specialised cells or organs.

Types of auxin

Auxin

Occurrence-growing tips

Precursor-tryptophan and zinc

Transport-basipetal and acropetally

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• Agricultural role:
• Parthenocarpic fruits
• Eradicate weeds
• Induce flowering in pine apple and cucurbits

Physiological effects

• Cell elongation.
• Apical dominance.
• Initiation and promotion of cell division.
• Formation of callus in tissue culture elongation of root.
• Prevent abscission.
• Stimulate respiration and differentiation.

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Bioassay-auxin�Avena curvature test[Went experiment]

Gibberellins

DISCOVERY-

• Kurusawa-foolish disease of rice.
• Yabuta and sumiki-Gibberellins isolated.
• Brain et al-named.
• Cross et al – structure.

OCCURRENCE- Young parts.

PRECURSORS-Terpenoids.

• IPP(Isopentenyl pyrophosohate).
• Acetate.

• Chemical structure-gibbane ring.
• Trasport-non polar.
• Bioassay-Dwarf pea assay.

Physiological effects of Gibberellins

• Extra ordinary elongation.
• Made to flower.
• Seedless fruits.
• Bolting for uniform seed production.
• Elongation of internode.
• Improve number and size of fruits.
• Stimulate germination.

cytokinin

Discovery

• Haberlandt-coconut milk.
• Miller and skoog-kinetin.
• Letham-term introduced.
• Letham and miller –zeatin.
• Occurrence-young parts.
• Precursors-purine adenine.
• Bioassay-neem cotyledon assay.
• Transport – xylem and phloem.

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Physiological effects of cytokinin

• Promote cell division.
• Break the dormancy of bud.
• Promote the growth of lateral bud.
• Delay the aging process called Richmond long effect by nutrient mobolization.
• Increase the rate of protein synthesis.

Ethylene

• Discovery

Denny-lemon.

R.Gane-banana.

cocken-identified.

• Occurrence

undergoing senescence cells.

• Transport: through intercellular space.
• Bioassay : Gas chromatography.

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Physiological effects of ethylene

• Ripening fruits.
• Stimulate the radial growth.
• Formation of Abscission zone.
• Root initiation.
• Epinasty.

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Climacteric fruits and non climacteric fruits

Climacteric fruits

• Rise in respiration rate.
• 1ppm ethylene promote ripening.
• Ethophon liquid used in ripening.
• example:Apple,tomato and Banana.

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Non climacteric fruits

All fruits cannot be ripened by exposure of ethylene.

example:Grapes, watermelon .

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Abscisic acid[stress phytohormones]

• Discovery:
• Addicott-Abscissic acid II
• Cornforth –Abscissic acid
• Precursor:Mevolonic acid
• Transport:diffusion, phloem and xylem.
• Chemical structure:Carotenoid
• Bioassay:Rice coleoptile assay

Physiological effects of Abscissic acid

• Closure of stomato
• Spoil chlorophyll and protein.
• Inhibition of cell division
• Induce bud and seed dormancy
• Promote abscission
• Antiauxin and antigibberellin property.
• Water stress hormone.

Plant movement

Definition:

• Plants have the capacity for changing their positions in response to external stimuli which are known as plant movement.

Types of plant movements

Types Of Para tonic Movements

Types of vital movements-�movement of locomotion

Autonomic movement

Movement arising

from internal stimuli of plant

Ex: chlamydomonas

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Paratonic

Movement arising

from externel stimuli.

types of movement- Movement of curvature

Atonomic(growth)

Atonomic (variation)

Tropic movement

• Geotropism

response to gravity

stimulus.

Types

Positive geotropic-primary root.

Negative geotropic-stem.

Diageotropic – secondary root .

Plageotropic – secondary lateral root.

Apogeotropic –not response to gravity.

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Nastic movements

• Seismonastic

• Thigmonastic

Photoperiodism in Plants

Vernalization�� - Definition� - Mechanism of vernalization� - Technique of vernalization� - Devernalization� - Practical applications�

Senescence �Phytogerontology�Types of senescence in plants ��

Programmed cell death�Senescence of an individual plant cell��

PHOTOPERIODISM

The physiological change on flowering due to relative length of light and darkness is called Photoperiodism.

• Biloxi variety of soybean
• Maryland mammoth variety of tobacco

The photoperiod required to induce flowering is called critical day length

• Nicotiana tabacum-12 hours
• Xanthium pensylvanicum-15.5 hours

Photoperiodic stimulus on cocklebur plant

Vernalization and flowering

Many species of biennials and perennials are induced to flower by low temperature exposure (0^oC to 5^oC). This process is called Vernalization.

• The term Vernalization was first used by T. D. Lysenko (1938)

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Practical applications

1. Vernalization shortens the vegetative period and induces the plant to flower earlier.
2. It increases the cold resistance of the plants.
3. It increases the resistance of plants to fungal disease.
4. Plant breeding can be accelerated.

Seed germination

The activation and growth of embryo from seed into seedling during favorable conditions is called seed germination.

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Types

Epigeal germination - elongation of hypocotyl

Hypogeal germination - elongation of epicotyl

Seed dormancy

The condition of a seed when it fails to germinate even in suitable environmental condition is called seed dormancy.

• Imposed dormancy is due to low moisture
• Innate dormancy is related to properties of seed itself.

Methods to breaking Dormancy

1. Scarification –mechanical or chemical treatment
2. Impaction – shaken vigorously to remove plug
3. Stratification –seeds exposed to moist condition for weeks to months
4. Alternating temperatures –alternation of low and high temperature
5. Light –dormancy of photoblastic seeds broken by exposing to red light

Senescence

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Collective, progressive and deteriorative processes which ultimately lead to complete loss of organization and function.

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The branch of botany which deals with ageing, abscission and senescence is called Phytogerontology.

Different types of Senescence

Programmed Cell Death (PCD)

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Abscission is a physiological process of shedding of organs like leaves, flowers, fruits and seeds from the parent plant body.

Abscission

STRESS PHYSIOLOGY

Larrea tridentata

The study of functioning of plants under adverse environmental conditions is called stress physiology.

Jacob Levitt (1972) first used the term biological stress(plants) is “any change in environmental condition that might adversely change the growth and development of a plant”.

Strain

The reaction of plants facing stress is called strain.

Eg. Reduction in photosynthesis

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Elastic biological strain

(returns to its original state)

Eg. Temporary wilting

Patterns of survival under stress

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• Stress resistant or stress tolerant plants

Some plants get adapted to stress condition and are not adversely affected by stress.

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• Stress enduring plants

Some plants cannot face stress and they pass their adverse period in dormant state.

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• Stress escapers

Ephemeral plants are short lived desert plants, which complete their life cycle during the seasonal rains before the onset of dry season.

How plants responds to

environmental stress

Environmetal stress

Resistance

Susceptibility

Survival and growth

Death

Stresses trigger a wide range of plant responses:

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- altered gene expression

- cellular metabolism

- changes in growth rates and crop yields

Classification of Stress types in plants

Biotic Stresses

The adverse effects on plants by other living organisms (viruses, bacteria, fungi, parasites, insects, weeds and competing plants.) also by man cutting plants.

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Potential biotic stresses: These are ever present in the environment such as bacteria, fungi and nematodes.

i. Allelopathy (Hans Molisch 1937)

Gr. Allelon: each other

pathos: to suffer

An organism producing one or more biochemical (allelochemicals) substances that greatly influence the germination, growth and reproduction of other organisms is called allelopathy.

• Positive allelopathic
• Negative allelopathic

Allelopathic plants and their action

ii. Pathogenecity

The effect of microbes that cause diseases in plants. Example: Xanthomonas citri

Xanthomonas citri

2. Abiotic Stresses: Abiotic stress may occur due to anatmospheric condition (atmospheric stress) or soil condition (edaphic stress).

Mastigocladus grow

well at 85^oC to 90^oC in hot springs.

Frying Pan Lake, Largest Hot Spring in the World, New Zealand

(Mastigocladus grow

well at 85^oC to 90^oC in hot springs).

Creosote bush (Larrea tridentata) can survive water content drops upto 30%

Resurrection Plant 

Selaginella lepidophylla

Mechanism of Drought Resistance

Xerophytes are well adapted for drought

• They have developed structural or physiological adaptations.

Plants that avoid or postpone desiccation have evolved an alternative path by developing following mechanisms:

• Improved water uptake by roots
• Efficient water conduction by increasing and enlarging the conductive tissues.
• Restriction of transpiration- stomata present only on the lower epidermis and covered dense trichomes.
• Rolling of leaves- minimize the transpiring surface
• Water storage in succulent tissue (CAM plants)- water use conservatively.
• stress protein (dehydrin and osmotin)- protect the macromolecules,

cytoskeleton against denaturation.

Mechanism of Salt Resistance

Plants growing in high salt condition faces two problems:

1. Absorption of water from the soil with negative water potential

2. Interaction with high concentration of toxic sodium carbonate and chloride ions.

On the basis of salt tolerance plants are grouped into two categories:

• Halophytes-
• Euryhaline resist a range of salt concentration.
• Stenohaline narrow range of resistance.

2. Non-halophytes or glycophytes

• Non-halophytes cannot resist salts as the halophytes. Helianthus annus tolerates high Mn⁺⁺ .

Following mechanisms:

• Excess of salt creates comparatively more negative osmotic potential so that the plants tend to lose water into surrounding medium.
• It is possible only if they absorb excess of salt and accumulate it in their cell saps to maintain the same or higher concentrations as those of outside plants.

Salicornia - A salt tolerant species

The drawbacks in Salt stress:

1. Salt accumulates in the vacuoles

2. The plants become succulents

3. Accumulated salt dehydrates the cytoplasm

4. Sodium chloride cannot be tolerated in the cytoplasm and

it denatures several enzymes

Proline and Betalin (osmoregulators)

Plants tolerate the salt stress by synthesizing organic compounds that can exist at high salt concentrations without denaturing the enzymes. These organic compounds are

called nontoxic organic osmotica.

Minuartia verna

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