3.6 plant hormone

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HOW TO RIPEN GREEN TOMATO?

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Biology Form 5Chapter 3 : Coordination & Response

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12.6 UNDERSTANDING PLANT HORMONES

How to ripen green tomato?

Plant Hormones12.6 UNDERSTANDING PLANT HORMONESA.k.a phytohormonesA group of naturally occurring organic compounds that influence physiological process at low concentrationUsually produced in one part of the plantTranslocated to another part of plant when they actPlant HormonesPlant need hormones to:Allow them to respond to environmental factorsEnvironmental factorsCO2O2ToxinsGravityTemperatureSunlightParasitesPathogensControl plant growth, development and movementExample of plant hormones:AuxinsGibbrellinsCytokininsAbscisinsEthylene or etheneauxinGreek (to grow)E.g. indoleacetic acid (IAA), zeatin (natural) & kinetin (synthetic)Promote cell elongation & cell enlargementProduce at stem tips, root tips (root caps), stems & budsRequired by plants almost all the timeInvolved in phototropism & geotropismAuxins

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Auxin in geotropismMajor effect is on stem elongation ; important in the regulation of heightHave little effect on rootsProduce at seeds, fruits & young leavesOnly required at certain times to induce major developmental changes (stem elongation)

Gibberellins

Stimulate cytokinesis (cell division) & influence cell differentiationProduced in all actively growing tissues (meristematic tissue)Often act together with auxinsCytokinins

Promote stomatal closure, prolong seed dormancy & stimulate shedding of leaves, flowers and fruitsMostly synthesized in mature leavesAbscisins

A gas; transported by diffusionPromotes flower opening and fruit ripeningAlso stimulates:Defence response to wounding/ infection of diseaseShoot growth & differentiationRoot growth & differentiationLeaf & fruit abcissionEthylene or etheneThe use of hormones in agriculturePromote growth of rootsStimulate parthenocarpy formation of fruits without fertilisationHerbicidePrevent fruit from dropping before harvest is dueAuxins

Promote fruit ripeningInduce flowering in pineappleIncrease latex flow rubber treesPromote female flower productionEthylene / ethene+ auxins = stimulate the production of shoots & roots in tissue cultureProlong the storage life of vegetablesCytokinins Increase production of bigger & more uniform bunches of seedless grapesIncrease sugarcane yieldIncrease flower bud production and stimulate their early floweringGibberellins