Next generation plant growth regulators in

horticulture production

Credit Seminar

Plant Growth regulator?

• An organic compound,

• Can be natural or synthetic,

• It modifies or controls one or more specific

physiological processes within a plant but the

site action is different.

Classification of PGRP’s

NO Growth regulator Example

1 AUXINS IAA, IBA, NAA, 2,4-D

2 Gibberellins Gibberellic acid

3 Cytokinins Kinetin, Zeatin

4 Ethylene Ethylen

5 Dormins Abscissic Acid

6 Flowering hormones Florigen, Anthesin, Vernalin

7 Miscellaneous natural substances Cyclitols, Vitamins, Phytochrome, Traumatic substances etc

8 Phenolic substances Coumarin

9 Synthetic growth retardants CCC, Phosphon D, Morphactons, Maleic hydrazode (MH) etc.

10 Miscellaneous synthetic substances Synthetic Auxins, synthetic cytokinins etc.

Major classes of PGR’S

1. Auxins

2. Gibbrellins Plant Growth

Promoters

3. Cytokinins

4. Ethylene

5. Abscisic acid

Plant Growth Inhibitors

Auxins• The Word Auxins originally derived from the

Greek word (auxein)- ‘’To grow/Increase”.

• First Isolated from human urine.

• Produced by the growing apex of stem and

roots of the plants

Types f Auxins

Natural

Synthetic IBA, 2,4-D, NAA

Indole -3- Acetic acid (IAA)

Signal-transduction pathways in plants

Gibberellins• Second most important growth Hormone.• Gibberellins are named after the fungus

Gibberella fujikuroi which causes rice plants to grow abnormally tall.

• synthesized in apical portions of stems and roots.

• More than 60 types of Gibberellins are known.

Cytokinins• First time isolated from coconut milk.

• Synthesized in root apex, endosperm of

seeds, young fruits, where cell division

takes place.

Abscic Acid• Also known as dormins, which acts as

anti-Gibberellins.• It is Synthesized in leaves of wide variety

of plants .• Responsible of closing stomata during

drought condition, hence acts as plant stress hormone.

The new generation of phytohormonsThe list of phytohormones expanded to include new chemicals :1. Brassionosteroids (BR), 2. Jasmonic acid (JA),3. Salicylic acid (SA),4. Polyamines,strigolactones (SL), 5. Nitric oxide (NO) and 6. Peptide hormones (Santner et

al., 2009)

Brassinosteroids (BRs)• Brassinosteroids (BRs), are class of plant

polyhydroxysteroids that recognized as new kind of phytohormones.

• The occurrence of brassinosteroids (BRs) has been demonstrated in almost every part of plants.

• about 70 BRs have been isolated from plants. (Bajguz and Tretyn, 2003)

THE CELLULAR MECHANISMS OF BR REGULATING PLANT DEVELOPMENTAt cellular levels, BRs can regulate• cell elongation• cell division• cell differentiation• At whole-plant levels, BRs can regulate• Hypocotyl elongation• Root and shoot development • Leaf developmentt• Male fertility• Senescence • Responses to biotic and abiotic stresses

A Graph shows the Roles of BR s in Regulating Plant Development

jasmonic acid (JA)• Jasmonic acid (JA) is derived from the fatty

acid linolenic acid It is a member of the

jasmonate class of plant hormones.

• The major function of JA and its various

metabolites is regulating plant responses to

abiotic and biotic stresses as well as plant

growth and development

jasmonic acid (JA)•  Regulated plant growth and development

processes include growth inhibition, senescence,

flower development and leaf abscission.

• JA is responsible for tuber formation in potatoes,

yams, and onions.

• It has an important role in response to wounding

 of plants and systematic acquired resistance.

jasmonic acid (JA)• Levels of jasmonic acid rise in response to

damage .

• The action of jasmonic acid induces the transcription of many genes involved in plant defense.

Salicylic acid• Salicylic acid is a monohydroxy benzoic acid,

a type of phenolic acid and a betahydroxy acid.

• Colorless crystalline organic acid 

• widely used in organic synthesis and functions

as a plant hormone.

• Derived from the metabolism of  salicin.

• Phenolic compounds exert their influence on physiological and biochemical processes including, photosynthesis, ion uptake, membrane permeability, enzyme activities, flowering and growth and development of plants.

ROLE OF SALICYLIC ACID

Case study

Bean (Phaseolus vulgaris L.) and tomato (Lycopersicon esculentum L.).

Fourteen day-old plants were soil-drenched with 20 ml of distilled water or 0.05, 0.1, 0.5, 1.0 and 5.0 mM ASA or SA.

Alternatively, seeds were imbibed in the solutions for 24 h and sown in pots.

• One week after soil-drenching or three weeks after the seed treatment, seedlings were subjected to heat, cold and drought stresses. For heat treatment, seedlings were exposed to 54 0.5 C for 3 h with an average light intensity of 40 Mol m−2sec−1 and then returned to room temperature. For chilling stress, plants were exposed to 0 0.5 C in an incubator with an average light intensity of 35 Mol m−2sec−1

• and 16/8 h light/dark photoperiod for two days.

• Drought stress was imposed by withholding water for 7 days, then on the 8th day all pots were watered until saturation.

Survival (%) of SA or ASA – treated tomato and bean plants after heat, cold and drought stress

• Bean plants A) exposed to heat stress • B) pre-treated as a soil drench with 0.5

mMASA and exposed to heat stress

• Bean plants A) exposed to heat stress • B) pre-treated as a soil drench with 0.5 mMASA and

exposed to heat stress

C) Exposed to chilling D) pre-treated as a soil drench with 0.5 mM ASA and subjected to chilling

E) subjected to drought F) pre-treated as a soildrench with 0.5 mM ASA and subjected to drought.

• The physiological and biochemical basis molecular biology of

SA induced SAR is not clear at present.

• The similarity of the injury mechanism between pathogenesis

and stress leads us to hypothesize that SA which induces

resistance to disease also confers tolerance to environmental

stress.

• Salicylic acid (SA) and acetyl salicylic acid (ASA) provide

multiple stress tolerance in plants and that salicylic acid and its

derivatives regulate the expression of stress tolerance.

Conclusion

Thank you…