• Plant Growth Regulator (PGR) also called as bio-stimulants or

bio-inhibitors, are organic compounds, other than plant

nutrients, that modify physiological processes in plant. PGR acts

inside plant cells to stimulate or inhibit specific enzyme or

enzyme systems and help regulate plant metabolism.

• PGR naturally produced in plants which control the growth and

other physiological functions, slightly away from its place of

production and active in very minute quantities.

Introduction

Name of PGR (Hormones)

Example / Trade Name

Auxins IAA, IBA, NAA

Gibberellins GA1, GA2, GA3,..…GA60

Cytokinenins Kinetin, Zeatin

Ethylene Ethylene

Abscissic Acid (ABA) Phaseic Acid, Dormins

Inhibitor Cycocel, MH-40

Common PGR

• Cell Enlargement: It stimulates cell enlargement and stem growth.

• Cell Division: It stimulates cell division in cambium and is used in tissue

culture plant production in combination with Cytokinin.

• Vascular Tissue Differentiation: It stimulates differentiation of phloem

and xylem.

• Root Initiation: It stimulates root initiation on stem cuttings. It is used in

tissue culture plant propagation for development of roots.

• Apical Dominance: It suppresses the apical shoot growth and promotes

the growth of lateral buds.

Role of Auxins

• Stem growth: Gibberelic Acid (GA) causes hyper elongation of stems by

stimulating both cell division and cell elongation. This produces taller

plants.

• Bolting in Long Day Plants: GA cause stem elongation in response to

long days.

• Induction of Seed Germination: GA activates germination of seeds

which otherwise require cold (stratification) or light to induce germination.

• Enzyme Production during Germination: GA stimulates the production

of enzymes like amylase in germinating cereal grains.

Role of Gibberellins

• Cell Division: Applications of Cytokinin along with auxins induce cell

division in tissue culture.

• Morphogenesis: In tissue culture, Cytokinin promote shoot initiation.

• Growth of Lateral Buds: Cytokinin applications can cause the release

of lateral buds from apical dominance.

• Leaf Expansion: Resulting solely from cell enlargement.

• Chloroplast Development: Application of Cytokinin leads to

accumulation of chlorophyll and promotes conversion of leukoplasts

into chloroplasts.

Role of Cytokinins

• Stomata Closure: Water shortage brings about increase in ABA level, leading to stomata closure as a response to water stress.

• Growth Inhibiters: ABA inhibits shoot growth but has less effect on root growth.

• GA Counteracts: ABA counteracts the effect of gibberellins on a-amylase synthesis in germinating cereal grains.

• Induced Dormancy: ABA affects induction or maintenance of dormancy in seeds.

Role of Abscissic Acid (ABA):

• Fruit Ripening: Ethylene in the form of gas helps ripe fruits in natural

conditions.

• Induction Of Femaleness: Promotes production of female flowers in

cucurbits (cucumber, squash, melon) to increase the yield.

• Flower Opening: Promotes of flower initiation and controlled ripening

in pineapples.

• Leaf and Fruit Abscission: Accelerates fruit abscission for

mechanical harvesting in fruit crops like grapes, cherries, and citrus.

Role of Ethylene