Identification of pt growth regulators.pptx

Types of plant growth regulators

1. Ideation of Plant growth regulators Plant growth regulators are biochemicals produced in plants (endogenous) or synthetic substances applied to plants externally(exogenous) which cause modification in plant growth & development . Plant groth regulators produced by plants called as phytohormones . This substances help in increased production of roots, shoots flowers etc. The PGRs can be broadly divided into two groups based on their function in a living plant body.   Plant growth promoters : PGRs which are involved in growth promoting activities, such as cell division, cell enlargement, pattern formation, flowering, fruiting and seed formation are called plant growth promoters . e.g., auxins , gibberellins and cytokinins .   Growth retardants or Inhibitors : PGRs of the other group play an important role in plant responses to wounds and stresses of biotic and abiotic origin and are called as Growth retardants or Inhibitors . They are also involved in various growth inhibiting activities such as dormancy and abscission. Eg : Abscisic acid & ethylene

2. There are five major types of Plat Growth Regulators (i) Auxins (ii) Cytokinins (iii) Gibberellins (iv). Ethylene (v) Abscisic acid 1.Auxin : These plant hormones are specially concerned with cell enlargement or the growth of the shoots Physiological function of Auxins : Cell Elongation : 2,4-D Root Initiation in stem cuttings : IAA , NAA , 2,4-D, naphthalene acetamide ( NAd ) etc. Auxin -induced rooting helps propagation of certain plants by cuttings . Apical Dominance: If the apical bud is intact on the plant, the growth of the lateral buds remains suppressed. Upon removal of the apical bud, the lateral bud nearest the apical bud establishes its dominance over the remaining buds, causing them to become in active again. This inhibitory effect of a terminal bud upon the development of the lateral buds is called apical dominance and produces a cone-shaped plant . Delay (or inhibition) of abscission of leaves : The abscission of leaves can be delayed or inhibited by the application of auxins on the surface of the lamina or on the cut surface of a debladed petiole.

3.   2. Gibberellins: A Japanese scientist Kurosawa found that the rice seedlings infected by the fungus Gibberella fujikuroi grow taller and turned very thin and pale. An active substance was isolated from the infected seedlings and named as Gibberellin. These are diterpenoids , with a gibbane ring structure. They have the ability to elongate the stem of green seedlings especially certain dwarf and rosette types . Functions of Gibberellins : Stimulate stem growth through cell elongation and cell division. Involved in overcoming dormancy in seeds and buds . It causes internodes to stretch in relation to light intensity. Used commercially in stimulating seed germination & seedling growth Stimulate development of flowers . Increasing fruit size of seedless ( Parthenocarpy ) in grape Delay Senesence : Increase photosynthesis and proteins synthesis and thereby decrease abscission Break dormancy and promote leaf expansion

4. 3. Cytokinins : Cytokinins are first isolated from Coconut milk . Miller & Skoog and their co-workers isolated the growth factor responsible for cellular division from a DNA preparation calling it as cytokinins in (1950). These are synthesized in root apex , endosperm of seeds, young fruits where cell division takes place. eg : Zeatin .   Functions of Cytokinins : Cytokinins promote cell division (Cytokinesis) Contribute to cell elongation in leaves Stimulate cell differentiation in combination with auxins .

5. 4. Ethylene : Ethylene gas is the byproduct of gas combustion and that this gas could affect plant growth. This same gas was naturally produced by plants and it caused faster ripening of many fruits. Ethylene is a gaseous hormone and it produce throughout the plant . Large amounts are released into the air by roots, the shoot apical meristem, nodes, senescing flowers and ripening fruits.   Functions of Ethylene in Plants: Inhibits root and shoot initiation by blocking the transport of auxins from apical meristems and controls stem elongation. Stimulates leaf curling ( epinasty ) Stimulates fruit ripening Because of this activity, ethylene is known as ripening hormone. Promotes flowering in Mango, pineapple and some ornamentals . Hastens leaf abscission and falling down of leaves due to formation of abscission layer. Determines sex expression in monoecious plants, plants that produce both male and female flowers on the same plant. Application of ethylene causes more female flowers in cucurbits .

6. Abscisic Acid (ABA ): The plants also do possess a few substances which inhibit growth. They retard such processes as seed germination, root and stem elongation and bud opening. As a matter of fact, the growth inhibitors act as chemical check upon plants preventing the seeds from germinating and the buds from opening under unfavourable conditions.   Physiological Role in Plants:   i. Closure of Stomata : During drought, leaves synthesize large amounts of ABA which causes stomata to close. Thus, ABA acts as a messenger and enables plants to conserve water during drought   ii. Delays seed dormancy: Applying ABA delays seed germination . It controls bud dormancy, counteracts the effects of other hormones. It inhibits cell growth that is promoted by IAA. It inhibits amylase production that is induced by Gibberellins thus delaying seed germination. It induces chlorosis and senescence unlike cytokinins that promote rejuvenation of leaves and delay senescence.

7. List of Plant Growth Regulators Marketed in India: AUXINS Formul ation Dose Product Name Crops 2-(1-naphthyl)acetic acid SL 45 g/l Planofix Apple Pear Pineapple 4-indol-3-ylbutyric acid DP 1 g/kg Seradix B No 1 Ornamentals 4-indol-3-ylbutyric acid DP 3 g/kg Seradix B No 2 Ornamentals 4-indol-3-ylbutyric acid SL 8 g/kg Seradix B No 3 Ornamentals GIBBERELLINS Gibberellins SL 32 g/l ProGibb 4% Grape, Pear, Citrus, Potato, Mango, Hops, Grape-seedless CYTOKININS 6-benzyl adenine/gibberellins SL 19/19 g/l Promalin Apple, Plum, Flowers, Ornamentals ETHYLENE Ethephon SL 480 g/l Ethrel Apple, Citrus, Cotton, Grape, Sugarcane Tobacco GROWTH RETARDANTS Paclobutrazol SC 250 g/l Cultar Litchi Mango Peach Plum Daminozide SP 850 g/kg B-Nine SP Flowers Ornamentals Glyphosate- isopropylamine SL 360 g/l Glyphosate 360 Acid Sugarcane and Grasses Glyphosate- isopropylamine SL 360 g/l Mamba 360 SL Sugarcane Grasses Glyphosate- isopropylamine SL 360 g/l Roundup Grasses Sugarcane Glyphosate- isopropylamine SL 360 g/l Roundup Ultra Sugarcane Grasses GROWTH INHIBITORS Mepiquat chloride SL 50 g/l Pix Cotton Chlormequat chloride SL 750 g/l CeCeCe 750 Pear, Wheat Chlormequat chloride/ethephon SL 300/150 g/l Uprite Wheat DEFOLIANTS Thidiazuron / diuron SC 120/60 g/l Dropp Ultra Cotton