Important notes of plant Hormones (plant growth regulator).

1. CHAPTER 15
PLANT GROWTH AND DEVELOPMENT
CATALLYST CATALLYST CATALLYST
A ACADEMY
BY

2. PLANT GROWTH REGULATOR :
PLANT GROWTH PROMOTOR (PGP) PLANT GROWTH INHIBITOR (PGI)
1) AUXIN ( INDOL DERIVATIVES) AA
TRYPTOPHAN
2) GIBBERLIC ACID ( TERPENE DERIVATIVES)
3) CYTOKININ (N6 FURFURYL AMINO PURINES)
ADENINE-PURINES
ABA ( ABSCESIC ACID)
CAROTENOIDS DERIVATIVES
ABSCISIN II ( DORMIN)
 ETHYLENE ( ETHYPHONE – GAS at room temp. ) PGA AND
PGI BUT, MORE PGI. ( C2H4 )

3. 1. AUXINS (increase/grow/enlarge) (IAA derivatives) (ACIDIC)
DISCOVERY:
• Charles Darwin and son Francis Darwin – coleoptile of canary grass, observe photoperiodism and bending of
coleoptile towards light.
• Serendipity found that coleoptile is source of auxin. After decapitation coleoptile cant grow.
• F.w.went isolate auxin from coleoptile of Avena sativa (common oat) by agar plate method.
• Kogl - smith was first isolated auxin from human urine.(from pellagra patient)
• Pellagra is a urinary disease caused by deficiency of AA tryptophan and niacin (vit.b3).
BIOASSEY:
Test to determine the functions of hormone and conc. of that at particular role .
Test : Aveno coleoptile curvature test.
ROLE :
1) Auxins help to initiate rooting in stem cutting.(in propagation). Adventitious root grow from callus.
2) It promotes Apical dominance helps to tea plantation ,hedge making in gardens.
3) It promotes abscission of old leaves and fruits ,and prevent early abscission in young leaves and fruits.
4) It promotes parthenocarpy in fruits e. g. Tomato.
5) It promotes flowering in pineapple.
6) Auxin acts as herbicide, weedicide. e.g. 2.4.D
7) Auxin controls xylem differentiation and cell division.
8) It also promote geotropism, phototropism ,and cell elongation.
EXAMPLE : NATURAL :IAA ,IBA . SYNTHETIC : NAA , 2 4 D.

4. 2) GIBBERLLINS (terpene derivatives) (acidic in nature)
more than 100 gibberellin reported from different organisms.
DISCOVERY:
• E. Kurosawa (1926) studied on rice plant disease – bakanae / foolish seedling disease. It causes due to
fungal pathogen Gibberella fujikuroi. ( MEMBER OF ASCOMYCETES )
• He isolate sterile filtrate of fungus ,and apply on plant to increase height ,later from that filtrate Gibberellic
acid were identified.GA3
• Site of synthesis – seeds ,nodes ,internodes.
BIOASSEY :
1) Barley endosperm test 2) dwarf pea plant bioassay
ROLE :
1) It increase the length of axis and stalk of grapes plant.
2) It increase length of internodes in sugarcane.( 20 tonnes/acre)
3) It promotes malting in brewing industries.
4) It delay senescence by increase ripening periods.( improve market value)
5) It hastens/increase juvenile phase ( 18 -20 yr) of conifers,(pines) for early seed production.
6) It improve shape and size in fruits e.g. pear ,apple etc.
7) It promotes bolting ( process in which biennial plants like cabbage ,beet internode elongation takes
place followed by flowering.) in rosette habit plants.
8) It promotes flowering in long day plant.
EXAMPLE :GA1 – GA105 (First discovered GA3).
9) It responsible for vernalization.

5. Commercial use of GA
Thompson seedless grapes (Vitis (Vitaceae family)
Without GA With GA
Larger fruits that are easier to clean are attractive in markets
shape and size in fruits e.g. apple
Bolting = internode elongation + flowering

6. 3) CYTOKININ(ADENINE DERIVATIVES) (Basic in nature)
DISCOVERY :
• F.Skoog and his co-worker miller working on tissue culture ,he observed that callus proliferated at internodal
segment of stem (pith cells) of tobacco only by, adding auxin as a nutrient with vascular tissue extract ,yeast
extract, coconut milk or DNA, cytokinesis promoted because any of these substances.
• Later Miller identified and crystallized these substance termed as KINETIN. Not occur naturally.
• It was isolated from herring sperm DNA (animal source) by autoclave process. And is modified form of adenine.
• Natural cytokinin - ZEATIN isolated from corn kernels and coconut water (plant source).
• Site of synthesis : root apices, shoot buds ,young fruits etc.(region of rapid cell div.)
BIOASSAY :
Delay in leaf senescence test (Richmond lang effect).
ROLE :
• It promotes division in young leaf, chloroplast, lateral
branch growth and adventitious shoot.
• It decrease apical dominance (against auxins).
• It promotes cell division.(cytokinesis)
• It promotes translocation of nutrients, which helps in delay
of leaf senescence.
EXAMPLE : Kinetin and zeatin.
 Cytokinin and auxins are
Antagonist for apical culture
Agonist for tissue culture.

7. 4) ETHYLENE : (GASEOUS PLANT HARMONE) precursor = methionine
DISCOVERY :
• In Germany (1910) H.M.Cousins confirmed the ripened orange produce a chemical which promotes ripening of
stored unripened bananas.
• Later identified these chemical as ethylene, gaseous PGR.
• Site of synthesis : all part of plant undergoing senescence and ripening fruits.
BIOASSAY :
Triple response test (apical hook, broadening of axis, horizontal growth of seed )
ROLE :
• It increase respiration rate during ripening of fruits. This increase rate of respiration is called respiratory
climactic.(climacteric fruits).
• Also ripening in non climacteric fruits.
• It promotes triple response in dicot seeds.
• It promotes root growth, formation of root hair by increasing surface area for absorption.
• It breaks seed dormancy in peanut, and break bud dormancy in potato tuber.
• It increase length of internode and petiole elongation in rice plants.
• It initiate flowering and synchronizing fruit set in pineapple.
• It induce flowering in mango.
• It promotes senescence and abscission in leaves and flowers.
EXAMPLE : ethylene (gas), ethephon (liquid).

8. Triple response in dicot seeds
Ripening of fruits.
Bud dormancy in potato
flowering in mango
Fruit set in pineapple

9. ETHEPHONE : ( Aqueous form of ethylene)
ROLE :
• It readily absorbed and slowly diffused form of ethylene.
• It promotes fruit development and ripening in mango, apple and tomato. Also ripened fruit by thinning
of wall in cotton, cherry, walnut).
• It promotes female flowering in cucumber (increase yield).by increasing reproduction.
• It widely used in agriculture.

10. 5) ABA (ABSCiSSICACID) : carotenoid derivative Natural Plant Growth Retardant.
DISCOVERY :
• During mid 1960s, three independent researchers reported purification and characterisation of 3 different
inhibitors
• inhibitor – B 2) abscission II 3) dormin
• Later it was named as ABA
• Site of synthesis : Leaf, Stomata and Seed.
ROLE :
• It is also known as stress hormone, because it stimulate closure of stomata and increases tolerant
capacity of plants to various external stresses.
• It act as inhibitor in plant metabolism.
• It inhibits seed germination. And promote abscission (leaf).
• It induces seed dormancy and helps seed to withstand desiccation (drying) and other unfavourable
conditions for growth.
• It helps in seed development, maturation and dormancy.
 Antagonist (Opposes) action to GA.(ABA-promote seed dormancy, GA-break seed dormancy)
EXAMPLE : Abscisic acid

11. ABA induces stomatal closure
Solutes (e.g. potassium
and chloride ions)
accumulate in guard
cells causing water to
accumulate in guard
cells, making them
turgid
ABA is one signal that
causes guard cells to
release solutes and
thus release water,
making them flaccid
and closing the stoma
(pore) between them

12. THANK YOU