1Hormones: communicating with chemicalsHistory- discovery of plant hormoneConcepts of hormones6 Major plant hormonesBalance of hormones regulate growth & development.Environmental signals can cause changes in hormone levels.Physiological effects- what changes does each hormone induce?Signal transduction- How does each hormone induce the response?19-1. History: Discovery of a growth substance (hormone- auxin)Growth substance is produced at one location and then transported to other parts of the plant.No lightCurvature was dependent on the conc of chemical (auxin)Form and function of multicellular organisms depend on efficient communication among cells and organs. Communication depends on chemical signals.Concepts1. Hormones are chemical signals that facilitate intercellular communication.Made in certain tissues and transported to target tissues.Act at very low conc.2. Level of hormones is regulated. By Rate of biosynthesisRate of degradation, andTransportLife time of chemical messenger is limited.3. Developmental/Environmental signals cause changes in hormonal balance.Environment cues ---> change [Hormone] --> responseDevelopmental cues --> change hormone levelsGrowth Regulation by Hormones6 types of hormones:1. Auxin: Stimulates cell elongation2. Gibberellin (GA): Broad functions , e.g.cell elongation, germination3. Cytokinin: induce cell division4. Abscisic Acid [ABA]: suppresses growth, "stress" hormone5. Ethylene: causes fruit ripening, abscission6. Brassinosteroid: BROther signaling molecules:Jasmonic Acid (JA): made in response to woundingSalicylic Acid (SA): aspirin, made in response to pathogen infectionSystemin2Hormones during seed development and germinationCKGA, IAAABAGAIAASeed germinationSeed developmenttime19-2. Taiz. Principal auxin in plants is IAASynthesized in shoot meristem, young leaves, developing fruits19-12: Taiz 1998. What controls auxin levels?Steady state levels of auxin depends on synthesis, degradation, transport and compartmentation.Auxins are synthesized from primary metabolites via multiple pathwaysAuxin is degradedby multiple pathwaysErythrose + PEPShikimic acid pathway19-11. Taiz. auxin is transported in a polar fashion.How? Model of polar auxin transport3A. PIN1 localizes to lower end of root cells.B. BFA causes PIN1 accumulation in intracellular compartmentsActions of AuxinCell elongation19-20 Taiz. What does auxin do?Auxin induces growth of oat coleoptile19-2. 18 h in water or auxin19-21 Taiz Auxin works at a narrow conc.rangeAuxin effects:Stimulate cell elongationPhototropismGravitropismHow does auxin cause these changes?Mode of action: [later]4Gibberellic AcidGA20-1. Taiz. Gibberellic AcidSynthesized in shoot tip and root tip20-9. Stem elongation correlates with GA levelBarley: GA stimulates food breakdown in seed germinationBolting involved in FloweringGA induce cabbage to bolt & flowerGA increase stalk length, thus grapes grow bigger.Sites of GA synthesisGAI promoter::GusMaking beer with GA1. Malting of barleySeeds are germinated (+GA) and then dried & pulverized.Malt contains starch-degrading enzyme & partially digested starch2. Mashing: water is addedStarch –amylaseÆmaltose (disaccharide) -ÆglucoseBoiled to stop the reaction.3. FermentationGlucose ---+ yeast---> ethanol CytokininAdenine ring521-1 Cytokinin is produced in root apical meristem21-7cytokinins regulate cell divisionInitiate chloroplast developmentEnhance cotyledon expansionDelay senescenceAbscisic AcidABASeed maturationStress ABA levels depend on Synthesis in leaves (chloroplast)Distribution within mesophyll cellImport from roots.DegradationExport23-1. Abscisic Acid- increase when environment favors slow or no growth. E.g. water stress, seed development-ABA increase in response to water stressImport of ABA via xylem to leaves ABA needed for seed development and inhibits premature germinationMutant of ABA synthesisSeeds germinate prematurelyVp14 maize6ABA levels depend onSynthesis in leaves (chloroplast)Distribution within mesophyll cellImport from roots.DegradationExportEthyleneH2C=CH2Ethylene gasEnvironmental stress promote ethylene biosynthesis.•Senescence•Fruit ripening•Shortening of dark-grown seedlingEthylene resistant mutant, etr1 is tall and cotyledons openfrom Kende 2001 PP.Ethylene induces responses in seedlings(dark). Ethylene is synthesized when seedlings encounter mechanical pressure.Hypocotyl thickensBent apical hookOnce seedling emerges above ground, the response to ethylene is