· Sequential process involved in growth: cell division → cell enlargement → cell differentiation.
· Maximum cell elongation occurs in the zone behind the root/shoot.
· Growth is Quantitive change.
· But, development is Qualitative + Quantitive.
· Growth is primarily affected by two climatic factors, which are light and temperature.
· During the growth there is an increase in dry weight, permanent change in size, volume, number of cells.
· Growth curve → S-shaped sigmoid curve.
· Growth is measured by Auxanometer, Horizontal microscope, Crescograph.
· The classical experiment in growth were performed by Boysen-Jensen and Darwin.

· Phases of Growth: 4 phases
i) Lag phase: Initial phase, slow cell division.
ii) Log phase(exponential): Maximum growth, fast cell division.
iii) Deaccelerating phase: Decrease in growth rate.
iv) Stationary phase: Constant growth.
· The plant growth is unlimited.
· Growth regulators are the organic substances that are required for growth and are called hormones.

· The term hormone was given by “Starling”.
· The existence of a growth-promoting substance in plants was given by Darwin observed in canary grass.
· Characters of Natural Hormone:
- Naturally produced organic
- Active in minute amount
- Act at a site remote from the site of its production i.e. they are produced in one part and transferred to some other parts, where their physiological effects are observed.
- May have promotors or inhibitory roles.
- Hormones are used up after biochemical reaction, while enzymes are unchanged after biochemical reaction.
- Hormones are synthesized in the meristematic region of plants.

· Hormones were originally measured with bioassay but now most of the hormones are measured by gas chromatography and immunoassay technique.

· Growth Hormones:
a) Growth Inhibitors: Ethylene and Abscisic acid (ABA)
b) Growth Promotors: Auxin, Gibberellin, Cytokinin
· 5 major types of Phytohormone are:
a) Auxin: 
Cell enlargement and differentiation.
b) Gibberlin: Cell enlargement and differentiation.
c) Cytokinin: Cell division
d) Ethylene: Senescence or Ageing
e) Abscisic acid: Bud dormancy and resting state.

1. Auxins:

· Auxin was discovered by F.W Went by Avena coleoptile curvature test.
· Bio-assay of auxin is Avena (oat) coleoptile curvature test.
· Naturally found in the apical meristem of the plants.
· Auxin A: isolated from human urine.
· Auxin B: isolated from corn grain oil.
· Heteroauxin: isolated from the re-examination of human urine by Kogl
· Also isolated from Rhizopus culture by Thiemann.
· True natural auxin is IAA, i.e, Indole-3-acetic acid.
· Heteroauxin is similar to IAA.
· Auxin for the first time was isolated from human urine.
· Synthesis of natural auxin takes place from amino acid Tryptophan.
(Note: Zn is needed for Auxin synthesis)
· Artificial/Synthetic auxins are:
a) IBA (Indole-3-butyric acid)
b) IPA (Indole-3-propionic acid)
c) NAA (Naphthalene Acetic acid)
d) 2, 4 Dichlorophenoxy acetic acid (Auxin used in war) (2,4-D)
e) 2, 4, 5-Trichlorophenoxy acetic acid (2, 4, 5-T)
· Natural auxin shows basipetal polar transport (shoot apex to base)
· Synthetic auxins have properties similar to natural auxins but doesn't show basipolar transport.

The functions of Auxin are:
1. Cell elongation:
· Rooting:
In root high concentration of auxin results in the formation of lateral roots and inhibit main root elongation. (IBA-Most potent root initiator)
- IBA → Promotes rooting in stem cutting.
- High auxin and low cytokinin promote rooting in callus.
- Less auxin and high cytokinin promotes shooting in callus
2. Apical dominance:
- Phenomenon of suppression of lateral buds due to the growth of apical buds.
- So lawn grasses are cut at the top to induce profuse lateral growth.
- Apical dominance of terminal bud is due to secretion of IAA.
· Synthesis of cell wall material.
· 2,4-D and 2,4,5-T are weed killers.
3. Generally auxin inhibits the flowering but in the case of litchi and pineapple, flowering is caused by 2,4 D and NAA.
· Note: Ethylene also induces flowering in pineapple.
4. Parthenocarpy: Auxins are used for the production of seedless fruit.
· NoteGibberellin also induces parthenocarpy in pome fruits and is more effective than the auxin.
5. Controls abscission of leaves and fruits (especially fruits).
· Note: Abscission is due to abscisic acid (also by ethylene).
6. Maintains dormancy (Inactive phase) of potato tubers, corms, and rhizomes.
· Note: Gibberellin breaks down the dormancy of potato tuber and also tree bud.
· Agent orange: Mixture of 2,4-D + 2,4,5,- (with dioxin)
· Note: It is used by the USA during the Vietnam war to defoliate forests.
· Sprouting of potato can be prevented by methyl ester (Maleic hydrazide).
· Note: Sprouting of potato during the storage is due to Gibberellin also causing parthenocarpy.
7. Seasonal activity of cambium and cell division is promoted by auxin.
· Concerned → Photorespiration and geotropism.
8. Auxin (IAA) is involved in photoperiodism.
· Nodule formation in legumes.

2. Gibberellin

· Yabuta and Hayashi discovered Gibberellin.
· Yabuta and Suniki isolated Gibberellin A and B.
· Firstly isolated from the fungus Gibberella fujikuroi or Fusarium moniliform (Belongs to Deuteromycetes)
· Disease caused by this fungus on rice seedlings is Bakanae disease or foolish seedling disease. Rice plant becomes abnormally tall.
· Gibberellin is synthesized in young leaves, buds, seeds and root tips.
· Most studied Gibberellin is GA3 (Gibberellic acid).
· Precursor of Gibberellin is 5-carbon compound
isopentenyl pyrophosphate.
· Test of Gibberellin: Dwarf maize/Dwarf pea test (or cereal endosperm test)

The functions of Gibberellin are:
1. Elongation of internode and leaf expansion. So genetically dwarf plant becomes tall after Gibberellin treatment.
(Generally, dwarf plants like pea and maize show the normal size in the presence of gibberellins due to stimulation of intermodal growth).
2. Bolting and flowering occur in rosettes like cabbage.
3. Breakdown of dormancy of potato tuber and tree buds. (Dormancy is maintained by Abscisic acid).
4. Induce germination in light-sensitive seeds. eg: Tobacco.
5. Induce parthenocarpy in those plants where auxins fail. eg; in some pome plants like apple, pear etc.
Note: Gibberellin is more effective than auxin for parthenocarpy.
6. Induce flowering in long-day plants under short-day conditions and inhibits in short-day plants.
Note: Cytokinin induces flowering in short-day plants.
7. Induce the number of male flowers in the monoecious plant (Cucumber).
Note: Ethylene promotes the formation of female flowers.
8. Gibberellin doesn't have an effect on the root.
9. Gibberellin increases the number and size of fruits. eg; grapes.
10. Increase sugar yield of sugarcane by promoting intermodal length.
11. Synthesis of 𝝰 amylase in the aleurone layer of endosperm during seed germination.

3. Cytokinin (Kinetin)

· Firstly isolated by Miller and Skoog from the old stock of Yeast DNA or denatured DNA.
· Accidently isolated hormone.
· Cytokinin induces cell division.
· Chemically identified as 6-furfuryl amino purine.
· Natural cytokinin: Zeatin (Coconut milk factor)
· Zeatin → pure natural cytokinin
    · Most active cytokinin.
    · Isolated from immature maize grain by Letham.
· Synthesized in endodermis, root tips and shoot tips.
· Bioassay for cytokinin is carrot root phloem test.

Test for Cytokinin:
· Richmond and Lang test → It is the test of ageing. Excised leaves remain fresh while kept in water containing cytokinin.

The function of Cytokinin are:
· Primarily responsible for cell division.
Note: Cell division in vascular cambium is by Auxin.
· Morphogenesis:
- Callus formation: If the concentration of Auxin and cytokinin are equal it will induce callus formation.
- Root initiation: If the concentration of auxin is high and cytokinin is low.
- Shoot initiation: If the concentration of auxin is less and cytokinin is high.
· Counteraction of apical dominance (promotes the growth of lateral buds)
· Induce formation of interfascicular cambium.
· Delay senescence/ageing. So cytokinin is used for the storage of leafy vegetables, flowers and fruits.
· Leaf fall can be prevented with the help of Cytokinins.
· Cell enlargement and expansion of cotyledons and foliage leaves.
· Cytokinin induces flowering in short-day plants under long-day conditions.
· It helps to retain the chlorophyll.

4. Ethylene

· Synthesized from amino acid methionine (precursor molecule).
· It is the only gaseous hormone.
· Synthesis is promoted by oxygen and inhibited by carbon dioxide.
· Also known as Ripening hormone.
· Synthesized in large amounts by tissues undergoing senescence and ripening fruits
· Produced at the root and shoot meristem.
· Ethylene is concerned with climacteric respiration.

The Functions of Ethylene are:
· Ripening and dehiscence of fruits.
· Ethylene generally inhibits flowering but in the case of pineapple and litchi, it causes flowering.
· Increases the number of female flowers in place of male Flower in the monoecious plant (Cucumber)
· It promotes abscission of plant parts (Can be prevented by Auxin)
· Induce epinasty or downward bending of leaves.
· Causes senescences (prevented by cytokinin)
· Promotes transverse growth of the stem. eg. Swelling of node, But inhibits longitudinal growth.
· Induce formation of adventitious roots.
· Break dormancy of different plant organs but not of lateral buds.

5. Abscisic Acid (ABA) or Abscisin II or Dormin

· ABA is called a DORMANT or STRESS hormone and is produced during adverse environmental conditions.
· It is a natural growth inhibitor.
· ABA is a mildly acidic hormone formed from Xanthophyll and Mevalonic acid.
· Produced in mature stem, leaf, fruit and seed.
· Most abundantly formed in chloroplast and are transported through all the parts of the plant by diffusion.
· It can be produced from the isolated chloroplast.

The function of ABA are:
· It hastens the process of senescence in leaves and leads to the falling of leaf (Abscission).
· Maintains dormancy of buds, seeds.
· Causes closing of stomata so-called as antitranspirant.
· It inhibits the activity of Cambium.
· It inhibits the conversion of starch to sugar by blocking the action of gibberellins.
· Functionally antagonistic to gibberellins.
· Protect plants from frost (i.e. low temperature), injury and desiccation.
· Caline (Formative hormone).
- Hormone responsible for root, shoot and leaf formation is called caline or formative hormone.
- Hormone responsible for root formation → Rhizocaline.
- Hormone responsible for shoot formation → Caulocaline.
- Hormone responsible for leaf formation → Phyllocaline.
· Traumatic acid (Wound hormone): Causes callus formation in the injured part.
· Hormone responsible for flowering is Florigen. Florigen is produced in the region of leaves.
· Vernalization: Low temp. (0-4 degrees centigrade) chilling treatment for early flowering in some winter annulus like wheat.
- Cold temperature for vernalization → perceived by shoot meristem.
- Light stimulus for photoperiodism → perceived by leaf.
· Hormone responsible for flowering under cold conditions is called vernalin.
· Senescence: it is the process of ageing that is caused by increased entropy, cellular breakdown, reduced homeostasis, increased metabolic failure and error of replication as well as transcription.
· A green plant will turn yellow if placed in the dark. This is called etiolation.


· Living plants have the characteristic of showing some changes in their position due to changes in the environment or due to some endogenous causes. Such changes are called movements.
· These movements are due to sensitivity or irritability of protoplasm.
· Stimulus, may be defined as any change in the external environment which produces a reaction (response) in the plant or plant organ.
· According to the nature of stimulus the movement may be autonomous (spontaneous), due to internal stimuli or paratonic (induced), due to external stimuli.
· The visible change or reaction of a plant or plant organ as a result of stimuli is called a response.
· The interval between the presentation of the stimulus and the actual development of response is known as reaction time.
· The minimum stimulus intensity required to induce a response is known as threshold intensity.
· Movement is not confined to the organism as a whole but occurs down to the cellular level. Eg; the cytoplasm of living cells constantly flows like a river in the cells, this streaming movement is called cyclosis.

Types of Plant Movement:
(a) Vital movement:

1. Locomotory (whole-body)
    - Paratonic (Taxis/tactic)
    - Autonomic
2. Curvature (parts)
    - Variaton → Paraton or Autnomic
    - Growth → Paratonic or Autonomic

(b) Non-vital movement (Non-living parts or body)
· Hygroscopic movement: Found in Bryophytes and pteridophytes. Eg; Twinning movement of elaters, peristome teeth, sporangial wall of fern.
· Paratonic: Induced by a stimulus like light, temperature, chemical.
· Autonomic: Spontaneous movement.
· Hygroscopic movement: Found in bryophytes and pteridophytes. eg: Twisting movement of elaters, sporangial wall of fern.

Movement of Locomotion:
· Common in lower plants.
A) Autonomic or Self-movement:
(i) Ciliary:
Movement due to cilia, flagella. Eg: Chlamydomonas,Volvox.
(ii) Amoeboid: Move, ent due to pseudopodia like structure. Eg: Synchytrium (slime mould)
(iii) Streaming movement/Cyclosis:
Two types:
(a) Rotation: Movement either in clockwise or anticlockwise direction i.e, movement in a single direction. Eg: Leaf of Hydrilla and Vallisneria.
(b) Circulation: Movement both in clockwise and anticlockwise direction, i.e. movement in all the possible directions. Eg; stamina hair of Tradescantia.

B) Paratonic or Induced movement:
· Also called as Tactic/Taxis movement.
i) Phototactic: Stimulus light. Eg: Zoospore of volvex and chlamydomonas
- Moves from dark to diffused light.
- Also moves from intense to diffuse light. (or vice versa)
ii) Thermotactic: Stimulus temperature. Eg: Chlamydomonas, Bacteria.
- Moves from cold water to warm water.
- Also from warm to cold water.
iii) Chemotactic: Stimulus chemical (Malic acid) Eg: Movement of antherozoids from antheridium to archegonium in bryophytes and pteridophytes.
iv) Rheotactic: Aquatic algae, Stimulus: water current.

Movement of Curvature:
· Common in higher plants:
Two types:
A) Movement of variation:
· Change in position without growth.
a) Autonomic: Eg: Leaves of Desmodium gyrans (Indian telegraph plant)
· The lateral leaflet always moves up and down.
b) Paratonicor Induced: Also called nastic movement.
i) Photonasty: Head of the sunflower. Also known as Helionasty.
ii) Thermonasty: Tulip (flowering at high temp.), Crocus flower.
iii) Nictynastic (sleep movement)– Light and temperature are both stimuli. Eg: Oxalis, Albizzia flowers are open in the day and closed at night.
· Oenothera: open at night and closed in the day.
iv) Seismonastic or Osmotic or Turgor movement: Eg: Leaves of Mimosa pudica (Touch me not plant)
v) Thigmonastic or Haptonastic- Stimulus: contact or Touch. Eg: Insectivorous plants (Movements of hairs in Drosera)

B) Movement of Growth:
· Change in position due to growth.
1. Autonomic Movement:

i) Hypnonasty: More growth of lower surface (abaxial)
- Plant parts moves upward.
Eg: closed flowers petal, young leaf of fern(circinately coiled leaf).
ii) Epinasty: More growth on the upper surface.
- Plants part move upward.
Eg: the opening of the flower is due to epinasty on a leaf, erect leaf of fern (matured leaf/frond).
Note: Hyponasty and epinasty are common in the bifacial structure like a leaf, sepal petal.
iii) Nutational movement: Alternate growth on either surface. Eg: Zig-zag growth of short apex, forward growth of branches

2. Paratonic Movement:
· Also called tropic movement.
i) Phototropic:
Roots are negatively phototropic and shoots are positively phototropic.
ii) Geotropic: Stimulus → Gravity.
  • Roots: +ve geotropic.
  • Shoots: –ve geotropic.
a) Orthogeotropic:
- Growth occurs parallel to the force of gravity.
· Eg: Main root (+vely orthogeotropic)
· Main shoot (-vely orthogeotropic)
b) Diageotropic:
- Plant part grow right angle to the force of gravity. Eg: Tertiary root, Rhizome, prostrate plants, leaves
c) Plageotropic:
- Plant part grows between 0-90/90-180 degrees.
· Eg: Secondary roots or lateral roots (+vely plageotropic), stem branches (-ve plageotropic)
d) Apogeotropic:
· There is no effect of gravity.
· Eg: Respiratory roots/pneumatophore of mangrove plants and coralloid root of cycas.
iii) Hydrotropism:
· Stimulus: Water, important for young roots
· Roots → positively hydrotropic.
· Stems → negatively hydrotropic.
iv) Thigmo or Haptotropism:
- Stimulus touch or contact. Eg: Tendrils bending on support, Haustoria in Cuscuta.
v) Chemotropic: Stimulus chemical (Maleic acid)
· Eg; growth of pollen tube towards the direction of embryo sac.
· Clinostat is an instrument to eliminate the effect of gravity on plants.
· Movement induced by injury is called Traumatropism.
· Time period between the perception of stimulus and reaction is called Reaction time.

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