This document discusses plant growth and development, including seed germination, the role of growth regulators (auxins, gibberellins, cytokinins, ethylene, and abscisic acid), and photoperiodism. It defines growth and outlines the phases and factors that influence growth. It describes seed dormancy and the changes that occur during seed germination. The roles and characteristics of the main plant growth hormones are summarized. The document also categorizes plants based on their responses to photoperiodism and defines vernalization.

1. PLANT
GROWTH

2. Growth can be defined as irreversible increase in the dry
weight & volume of an organism.
Introduction
Growth is due to cell division, cell enlargement &
maturation
The process marks completion by a) permanent change in
size & b) increase in dry weight.
Animal growth is uniform & limited but plant growth is not
uniform (growth is seen at tips) & unlimited.
Growth can be studied from the seed stage, a seed is made
up of embryo enclosed by endosperm finally seed coat.

3. Introduction contd….
Embryo further can be differentiated into radicle, plumule &
cotyledons (seed leaves). Radicle & Plumule form the embryo
axis & is also called as tigellum.
The point of attachment of cotyledons & embryo axis is
called as first node.
The part of embryo axis between first node & plumule is
called Epicotyle similarly the part of embryo axis between
first node & radicle is called Hypocotyle.
If endosperm persists the seeds are called
endospermic/albuminous & if the endosperm is used then the
seed is called as non-endospermic/exalbuminous seed. Testa &
Tegmen are the two seed coats.

4. Seed Dormancy (Rest)
Dormancy may be defined as the condition of the viable
seed when it fails to germinate even under favorable
conditions.
Quiscence It is defined as the condition of viable seed which
fails to germinate because of unfavorable conditions
Immature embryo’s
Factors affecting Seed Dormancy
Impermeable seed coat
Presence of germination inhibitors, eg: Abscissic acid,
Phenolics

5. Scarification of seed coat: Mechanical roughening of seed
coat, to make it pervious to water
Methods to induce germination
Stratification of seeds: Moist seeds are subjected to
temperature gradient, changing environmental conditions like
light, pressure, temperature.
Growth Regulators: Treating the seeds with Growth regulators
like Auxins, Giberellins etc.
Seed Germination
The resumption of active growth of an embryo of seed after a
period of dormancy is known as seed germination.

6. Cell enlargement (with the help of water)
Changes during Seed Germination
Hydrolysis Translocation of food
Conversion of food into simpler forms.
Types of Seed Germination
Epigeal (Cotyledons above the ground): Cotyledons are
pushed upwards above the soil due to elongation of
hypocotyle.
Hypogeal (Cotyledons remain below the ground):
Cotyledons remain below the soil due to elongation of
epicotyle.

9. Water: Increases permeability, essential for enzymatic activity.
Factors affecting germination
Oxygen: required for respiration & release of energy.
Temperature: Optimum temperature is 26 to 300C.
Light: Not an essential factor but some seeds germinate better
when exposed to light.
Characteristics of Growth
Meristematic tissue or Growing tissue is responsible for
growth. It is present in the apices of stem & root. According to
the origin meristems are of two types’ primary (increase in
length) & secondary. Secondary meristem is seen in vascular
bundle & cork cambium.

10. Growth Curve
It is a Sigmoid or S shaped curve. Growth curve shows
following three phases
Lag Phase – initial phase, slow growth
Log Phase – rapid increase in growth
Steady Phase – slow growth due to limitations of nutrients.

11. Phases of Growth
Formative Phase or phase of cell division
Phase of Elongation or enlargement
Phase of Maturation or Differentiation
Restricted to the apical meristems (root & stem)
Cell divide continuously, they show abundant cytoplasm,
distinct nucleus & thin cellulose wall.
Cells increase in size; cells elongate & enlarge to reach
maximum dimensions in this phase.
Cells mature & differentiate to obtain permanent size;
thickening of cell wall takes place
The time interval from formative phase to maturation phase is
called Grand period of Growth.

12. Factors affecting Growth
Temperature: Optimum temperature required for proper
growth should be 26 to 30oC, above 45oC protoplasm
coagulates & is damaged hindering growth.
Nutrients: They are required for synthesis of protoplasm
provide energy.
Water: Required to maintain turgidity of growing cells &
also as a medium for chemical reactions.
Oxygen: Indispensable for the process of respiration
releasing energy
Light: Not essential in initial stages but required later for
photosynthesis & thus stimulates growth.

13. Growth Regulators
Growth regulators are the main internal factors
controlling growth, also called as plant growth
hormones, Growth regulating substances. They are of
two types namely Natural & Artificial.
Properties of Hormones
Hormones are other than nutrients
They are required in less quantity.
They move from place of production to the site of action.
They have a broad action spectrum.
An organic substance produced naturally & controls
growth or other physiological process at a site away
from its place of production is termed as plant hormone.

14. Auxins
Tryptophan (Auxin precursor) is converted to form auxins.
Auxins are found in two forms Free Auxins (easy for isolation
or extraction) & Bound Auxins (Difficult to extract).
Free & Bound Auxins are always in a dynamic
equilibrium.
Anti auxins inhibit the action of auxins.
Chemical Nature
Chemical formula of auxins is C10H9O2N
Weak organic acids occurring in the form of Indole – 3 –
Acetic acid (IAA),.
Tryptophan  Indole Pyruvic acid / Tryptoamine 
Indole acetaldehyde  IAA
Tryptophan is produced in leaves

15. Went Avena Coloeoptile Test
3 cm long seedling of Avena is selected.
Tip is removed (decapitulation) & placed on Agar block.
Agar agar is a polysaccharide which acquires a gelatin
like consistency when dissolved in water & cooled.
Agar block is cut in to pieces, tips are discarded.
Agar block is placed asymmetrically on cut end of the
coleoptile for 2 hrs.
Curvature is observed.
Characteristics
Synthesis at shoot, root tips & young parts of plants.
Moves from top to bottom Inactivated by light
Higher concentration promotes stem growth & retards
the growth of root & axillary buds & vice versa.

16. Role
Stimulates cell division & elongation
Promotes apical dominance Induces root formation
Sex Expression – Increases number of female flowers
Induces formation of seedless fruits (Parthenocarpy)
Induces flowering in Litchi & Pineapple.
Prevents sprouting of potatoes when need to be stored
Prevention of lodging (falling of crops in windy season)
Maintains the vegetative condition by inhibiting flowering
which is required in crops like cabbage.
Prevents formation of Abscission layer
Prevents pre-harvest fruit drop
Xylem differentiation Used in Tissue culture
Weed Control – differential killing
(2,4 D kills broad leaved dicot weeds without harming monocot crops)

17. Gibberellins
Gibberellins were isolated from Gibberella fujikuroi
(fungus) by Yabuta & Sumiki.
Gibberella fujikuroi causes Foolish seedling of rice also
called Bakanae’s disease.
Such plants are unusually taller, seedless, thinner &
paler.
Chemical Nature
Chemical formula of Gibberellic acids is as follows
GA1  C19H24O6 GA2  C19H26O6
GA3  C19H22O6 GA4  C19H24O5
Acetyl Co A  Kaurene  Gibberellic Acid

18. Movement is non polar, lateral movement is also
possible. Not influenced by light
Characteristics
They are concentrated in the growing regions like shoot
apices, young leaves & embryos
Role
Stimulates rapid cell division & cell elongation leading to
elongation of internodes
Leaves become broader, increasing photosynthesis
resulting in increase in height.
Overcomes Dwarfism – Induces internodal growth in
genetically dwarf varieties (Dwarfism is due to deficiency of
Gibberellins, no additional internodes are produced but length of internodes
increases).

19. Internodes strikingly increase just before flowering, this
is termed as bolting, Gibberellins causes bolting &
flowering. (In nature it is favoured by either cold nights/long days)
Breaks dormancy & allows germination.
Flowering – induces off season flowering.
Role contd….
Modification of sex of flowers – induces production of
male flowers.
Formation of enzymes – mobilizes stored food during
seed germination& early seedling growth by forming
enzymes. (Proteases, Amylases, Lipases &
Ribonucleases).
Cold treatment is substituted
Parthenocarpy Delay ripening

20. Kinetin was isolated from Herring sperm of DNA.
Coconut Milk is a rich source of cytokinin.
Basic in nature, amino purines or phenyl urea
derivatives
Cytokinins
Zeatin (6-hydroxy 3-methyl trans 2-butenyl aminopurine) is the
naturally occurring cytokinin & Kinetin (6 Furfuryl aminopurine)
is an synthetic cytokinin.
Chemical Nature
C10H9N5O is the chemical formula, they are derivatives
of purine base Adenine, & amino group in 6th position
has many substitutes.

21. Synthesized in roots, movement is non polar.
Characteristics
Stimulates mitotic activity & found in areas of cell
division.
Counteracts apical dominance, delays senescence.
Nutrient transport – regulates phloem transport.
Cell Division – induces cell division & cell wall formation
Role
Flowering – induces flowering in few short day plants.
Cell Enlargement – induces cell division in leaf discs &
cotyledons
Seed Dormancy – breaks dormancy & promotes
germination.

22. Differentiation – induces plastid, trachied, interfascicular
cambium differentiation.
Role contd…..
Senescence / Richmond Lang effect – Delays
senescence by retention of chlorophyll & proteins.
Apical Dominance – activates growth of lateral buds thus
reducing apical dominance.
Morphogenesis – Changing the balance of Cytokinins &
Auxins initiates root/shoot growth.

23. Maximum production takes place in fruits before
senescence (only growth regulator in gaseous form).
Ethylene is a volatile gas produced through metabolic
process & also called as ripening hormone.
Ethylene
Chemical Nature
CH2=CH2 is a volatile gas.
Methionine  Methional  Ethylene
Methionine  4-methyl thio butyric acid  Ethylene
Movement is non polar, active in low temperature.
Characteristics
Synthesized in tissues undergoing senescence &
ripening.
Promotes abscission of leaves, flowers & fruits, inhibits
root & stem elongation in dicots.

24. Sprouting of storage organs.
Role
Sex expression – feminizing effect.
Epinasty – drooping of leaves.
Senescence – enhances senescence
Growth – stimulates horizontal growth in seedling
Wound Response – reduces stress/withst& infection.
Effect on flowering – stimulates flowering in pineapple.
Activation of enzymes – activates the action of enzymes.
Apical Dominance – promotes & prolongs dormancy of
lateral buds.
Fruit Ripening & climatic rise – production of ethylene
increases 100 times.

25. Abscission – promotes the changes that occurs before
abscission, enhances cell wall destroying enzymes.
Role contd….
Root growth – At low concentration stimulates root
growth, at high concentration root growth is inhibited.
Triple response – reduction in elongation, swelling of
epicotyl & change in direction of growth.

26. Production of this hormone is stimulated by drought,
water logging & other adverse climatic conditions.
Naturally occurring growth inhibitor, also called Stress
hormone.
Abscissic acid (ABA)
Chemical Nature
It is a 15 csron sesquiterpenoid, exists in positive (cis more
active) & negative (trans) form.
Trans form is converted in to cis in the presence of
ultraviolet light.
Synthesized in mature leaves & transported by vascular
tissues
Characteristics
Effective in low concentration, movement is non polar.
Inhibition of protein synthesis

27. Role
Abscission – causes leaf fall, Senescence – accelerates
leaf senescence
Seed & Bud dormancy – maintains dormancy
Release of Ethylene – stimulates release of ethylene.
Growth inhibition – inhibits action of growth promoters.
Flowering – promotes flowering in SDP & inhibits
flowering in LDP.
Water stress & antitranspirant – Causes closure of
stomata & retains water.
Resistance & tolerance – increases resistance to cold &
enables to withstand dessication.
Seed development & germination – inhibits development
& germination by inhibiting activities of many enzymes.

28. Characters Gibberellins
Examples
Movement
Auxins
IAA
Polar
Cytokinins
Developing
seeds, roots
Root, shoot tips
Coconut milk
Kinetin, Zeatin
Gibberellic
acids
Site
Main function Elongation of
cells
Cell division
Mode of action Incr. O.P,
permeability
Activates DNA
synthesis
Induces auxin
synthesis
Non-Polar Non-Polar
Elongation of
internodes

29. Gibberellins
Auxins Cytokinins
P
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f
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s
Cell division Cell division Stem elongation
Root initiation
Apical dominance
Prevents lodging
Shortens
internodes
Initiates flowering
promotes
femaleness
Parthenocarpy
Breaks dormancy
Prevention of
abscission layer
Weed control (2,4-D)
Cell enlargement
Reduces apical
dominance
Breaks dormancy
Delays senescence
Tissue
differentiation
Parthenocarpy
Initiation of intra-
fasicular cambium
Bolting
Flowering in biennial
plants
Induces male sterility
Parthenocarpy
Activates cell division
Breaks dormancy
Increases male
flowers
Delays ripening &
Scenscence in Citrus

30. Characters
Examples
Movement
Ethylene
Non Polar
Abscissic acid
Fruits, Flowers, leaves Mature leaves
Site
Main function Post harvest ripening Inhibits buds, seed
germination
Mode of action Activates respiration Inhibts protein synthesis
Non-Polar
Ethylene Abscissic acid
Causes Senescence
Causes early leaf fall
Causes abscission & leaf
fall

31. P
h
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s
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f
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Inhibits root & stem elongation Induces dormancy
Ethylene Abscissic acid
Initiation of flowering in
Apple,Pineapple & Mango
Forms adventitious roots
Increases female flowers
Epinsaty (downward rolling of leaves)
Induces apical dominance
Promotes abscission
Breaks dormancy
Promotes abscission
Suppresses germination
Closing of stomata (K+)
Encourages leaf senescence
by inducing loss of proteins &
chlorophyll.
Reduces rate of photosynthesis
Induces flowering in few SDP
Inhibition of shoot growth

32.  Photoperiodism:
 The effect of duration of light hours on the growth &
development of plants, especially flowering is called
photoperiodism.
 On the basis of the photoperiod plants have been
classified in to following categories:
 Short Day plants:
 They require shorter light period than their critical
period.
 Uninterrupted dark period is more important & not the
duration of exposure to light.
 If the uninterrupted dark period is less than critical
length, flowering does not occur.
 Eg. Chrysanthemum, Potato, Sugarcane, Strawberry etc.

33.  Long Day plants:
 They require longer period of light than their critical
period.
 Photoperiod may vary from 14 to 18 hrs, best flowering
occurs in continuous light.
 Darkness plays an inhibitory role. A flash of light during
long dark periods can induce flowering even during
short day periods.
 Shorter dark period is more important than light period.
 Eg. Spinach, Radish, Opium, Wheat etc.
 Day Neutral Plants:
 These plants flower irrespective of light & dark periods.
 Eg. Tomato, Cucumber, Sunflower, Maize etc.

34.  Vernelization:
 The method of inducing early flowering by
pretreatment of seeds with a certain low temperature is
known as vernelization.
 Mostly biennials & perennials require need
vernelization.
 Plants which can be vernelized are called inductive
type & the one which cannot are called non inductive.
 In cold countries there are two types of cereals Winter
& Spring.
 Winter cereals are sown in September/October
flowering in following summer whereas Spring cereal is
sown in Spring which flowers in Summer. If winter
cereals are sown in Spring they will flower in next
year’s summer i.e. they require chilling treatment.

35.  Devernelization:
 When plants treated with cold treatment are exposed
to higher temperature, the flowering did not occur this
phenomenon is called devernelization.
 Physiology of flowering in Petkus rye:
 In cold countries there are two varieties of Petkus rye,
winter rye & spring rye.
 Spring strain is annual, flowering & fruiting in one
growing season but winter strain is biennial i.e.
vegetative growth in the first season & flowering,
fruiting in the next season.
 Thus Petkus rye the winter variety can be vernelized in
the seed stage resulting in the production of flowers in
the first acting as the spring strain.