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 AuxinsIAA, IBA, NAA GibberellinsGA 1, GA 2, GA 3,..…GA 60 CytokineninsKinetin, Zeatin 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