Plant Growth Regulators (PGR)DefinationPlant growth regulatorsare the substances which regulates the growth of the plants.They act as bothgrowrh promoters and growth inhibitors.They are synthetically applied to theplants.

ClassificationThere are five mainclasses of plant growth regulators:1)     Ethylene2)     Auxin3)     Abscisic acid4)     Cytokinin5)      GibberellinEthylene:It is a gaseous compound. It plays animportant role in the growth and development of plant. Sweet in taste.Functions of Ethylene;Ø  Promote bud sproutingØ  Enhance seedgerminationØ  Promote ripeningØ  Cause senescenceØ  Play a function inwater logging soilØ  Promote growth anddevelopmentBiosynthesis of Ethylene; Methionine                Adenosyl methionine                SAM           ACC                EthyleneSources;      I.           Ethylene generator   II.           Smoke III.           Cac2Auxin:It is a plant growth promoter. It plays animportant role in the promotion of bud formation and root development.

It alsoinclude the 1-Naphtaleneacetic acid(NAA), Indole-3-butyric acid (IBA) Functions of Auxin;·        Promote the bud formation·        Initiate the root formation·        Regulate the cell enlargement·        Cause the apical dominance·        In seeds regulate the specific proteinCytokinin:It is a plant growth regulator. First cytokininwas named as zeatin which isisolated from the maize seeds.Functions of Cytokinin;o  To produce cell divisiono  Retard the senescenceo  Form the calluseso  Stimulate the development of lateral apiceso  Break the apical dominanceo  Promote abscission of leaves ,flower parts, fruitso  Promote shoot formationGibberellin:They are responsible forthe elongation of stem and other tissues. They were discovered by Japaneseresearch of a rice disease.Types;GA1, GA2, GA3Functions;a.       Mainfunction is stimulate the seed germinationb.      Itperform a specific function in the sex expression of the plantc.       Playan important role of transition from juvenile  period to the adult period of the plantd.

      Withthe auxin it stimulate the fruit setting in some speciese.       Applicationof this induce the floweringf.       Elongationof the stem and other tissuesAbscisic acid:Abscisic acid also called(ABA). It is most important plant growth regulator.

It was fond in highconcentration of the fallen leaves. It is inhibitory chemical compound whichaffect the bud dormancy and the seed dormancy. It also affect the growth ofbuds.Functions of ABA;§  Playsan important role in the seed germination§  Italso inducing the storage of protein synthesis§  Modulatingof the water stress§  Causethe abscission of the fruits and the leaves§  Itclose the stomata during drought condition and prevent from the dehydration§  Importantfunction in the leaves and seed dormancy§  ABAlevel increase and slow down the cellular growth in mature parts of the plants Use of Growth Regulators inHorticultural crops1)Propagation:Growth regulators areused in the propagation methods in the horticultural crops.

These can beapplied in the form of the solution and in the form of paste. The concentrationof these chemicals can be varies according to the plant species and applicationmethod. IAA, NAA, IBA are used indifferent propagation methods. Some plant growth regulators are used in thebudding, layering, grafting for getting the high success.2) Seed germination:They play an importantrole in the germination of seeds. Some growth regulators accelerate thegermination of seeds in some plant species.

Soaking with the gibberellin ofsugar beet and okra seeds enhance the germination.3) Expression of sex:Sex of the flowers arechanged by some growth regulators. These are used for inducing sterility ofmale. Malic hydrozide is used for inducing male sterility in the corn. Femaleflowers in cucumber and pumpkin are increased to get maximum yield by applying theNAA and GA.4) Flowering induction:Growth regulators areused for inducing flowering in different crops. NAA at the rate of 10 to 40ppmis used to early flowering of pine apple.

NAA at 200 to 700 ppm can delay theflowering for 1 to 2 weeks in plums. 5) Fruit and flower thinning:Used for thinning offruits and flowers on the tree which bear heavy flowers. NAA at 5-8 ppm is usedfor thinning of peaches and grapes and apples. NAA at 6 to 10 ppm used fornormal bearing6) Early maturity: Earlymaturity of fruits can fetch maximum price in the market. Many growthregulators are used for early maturity of different fruits. Early flowering andearly maturity can induce in pine apple by applying of  NAA at 20 ppm.

Maturity of grapes can reduceby applying of NAA at 50 ppm.  7) Fruit development:Some growth regulators are used for proper developmentof fruit. Berry size of grapes can increase by applying of GA at 50 to 90 ppm. 8) Delayed maturity:Plant growth regulators are also used in delayingmaturity of different fruit crops. Fruits take more time to mature. When fruitslike mangoes are sent to a long distance than the ripening of mangoes isdelayed by using different compounds. Storage life can increased by dipping thefruits in MH-40.9) Bud sprouting:Bud sprouting alsoinduced by applying of different compounds.

They enhance the activity ofsprouting in buds. Sprays of Cytokinin, IBA and GA induce the bud sprouting.10) Dormancybraking:Somegrowth regulators are used for breaking the dormancy of seeds and buds.

 GA and NA are the compounds which are used forbraking the bud and seed dormancy. 11) Colordevelopment:Colorsof different fruits can develop by dipping the fruits in specific growthregulators. Ripening process of  Banana andmango is fast. They ripe after the harvesting. Golden yellow color is attainedby dipping the mangoes in Ethrel solution at 20 to 40 ppm. This solution givethe yellow color to the fruits.

 

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