PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19C C ═ ═ CCC C ═ ═ CCHHHHHHHHHHHHHHHHChapter 22: Ethylene:The gaseous hormone1800s Coal-gas street lamps-early senescence1901Dimitry Neljubov—Triple responseReduced stem elongationIncreased lateral growth (swelling)Abnormal horizontal growth1910H.H. Cousins found that ethylene was a natural product of plant tissue1934R. Gane and others identified ethylene as a product of plant metabolism and classified it as a plant hormone1960-presentGas chromatography used in ethylene research, mutant analysisRole of ethylene in regulating plant functionEthylene: HistoryEthylene (C2H4) Ethylene oxidizes readilyEthylene is biologically active at less than 1 ppb (1 nL L-1) (gases are difficult to concentrate so plants must be sensitive)Ethylene is made in nearly all parts of higher plantsRate of production depends on tissue type and stage of developmentYoung leaves make more ethylene than fully expanded leavesMeristimatic and nodal regions produce high levels of ethyleneEthylene is produced in response to: Developmental shiftsStress responsesEthylene: properties and production C ═ CC ═ CHHHHHHHHEthylene control: 1) Synthesis 2) Catabolism/conjugation is less important3) Increase sensitivity (greater number of receptors)Ethylene biosynthesisMethionine is the precursor to ethylene synthesisThe Yang cycle conserves sulfurEthylene biosynthesisEthylene biosynthesis is directly regulated by ACC synthase and ACC oxidaseEthylene production is stimulated by ACC synthase stabilization (rate of enzyme break down by proteosome is decreased through phosphorylation)Oxygen required by ACC oxidase in the last step of ethylene productionBased on the graph what is the rate limiting step of ethylene production?What might explain ethylene production as illustrated by the dashed black line?Low O2(Ripening)Developmental changes:Seedling developmentFruit ripeningFlower senescenceLeaf senescenceStress response to:FloodingDroughtPathogen attackWoundingEthylene mediates:Ethylene breaks seed and bud dormancyEthylene causes the triple response in etiolated seedlingsPromotes lateral growth- cellulose microfibrils oriented verticallyApical hook: ethylene promotes auxin mediated asymmetric growthWhy lateral growth and hook?Red light (sensed by phytochrome) inhibits ethylene production equalizing the growth resulting in hook lossEthylene’s role in seedling developmentETR1: ethylene receptor mutantFacilitates soil penetration, protects apical meristemEthylene promotes (& accelerates) fruit ripeningFruit ripening: Softening due to cell wall and starch hydrolysisSugar accumulationOrganic acid disappearancePhenolic compounds (including tannins) disappearEthylene: Fruit ripeningSpike in ethylene levels leads to rise in respiration (measure of ripening) Ethylene spike is a result of autocatalytic ethylene production (ethylene stimulates its own production) Ethylene dependent climacteric fruit ripeningEvidence for ethylene involvement in fruit ripeningEthylene biosynthesis is blocked with antisense versions of ACC synthase or ACC oxidase in transgenic tomato Fruit doesn’t ripen Exogenously applied ethylene restored ripeningFurther evidence Never-ripe mutation (tomato) Found to be a mutation in an Ethylene receptorSilver thiosulphate (STS) inhibits ethyleneSilver thiosulphate (STS) inhibits ethyleneEthylene promotes flower senescenceWhy do plants have a flower senescence pathway? They’re so pretty.Ethylene promotes leaf senescenceWT + ethylene(50 ppm for 3 days)ETR1 + ethyleneEthylene stimulates leaf abscissionReductions in auxin increase ethylene concentrations and the sensitivity of the abscission zone to ethyleneEthylene stimulates root hair formationAirAir + ethyleneEthylene promotes stem elongation during floodingSubmergence (or treatment with ethylene) induces rapid internode or petiole elongationGrowth is stimulated because: Ethylene builds up in the tissue (in spite of low O2) because gas diffusion through water is slow Ethylene increases plant sensitivity to GA by antagonizing ABAEthylene produces aerenchyma in roots during floodingLotusAerenchyma are spaces that form in the cortical tissue of roots via cell deathHow would they benefit the plant root under flooding?Conduit for oxygen transportLess tissue results in lower oxygen consumptionEthylene signaling pathway is negatively regulatedEthylene signaling pathway is negatively regulatedIn the absence of ethylene ETR1 activates CTR1 which leads to a repression of the ethylene response pathwayThe binding of ethylene to ETR1 results in its inactivation which causes CTR1 to become inactiveInactivation of CTR1 allows EIN2 to become active which activates transcription factors that turn on gene associated with ethylene responses CTR1 mutantChapter 22 Homework QuestionsOutline how ethylene mediates lateral growth and apical hook formation in young seedlings. Explain why these two characteristics are important in early seedling development.What are three developmental processes that are promoted by ethylene toward the end of the growing season? Explain how each of these processes occurs and explain how they benefit the plant?What morphological changes are mediated by ethylene that helps plants cope with drought and flooding stress? Explain how these two stresses increase ethylene concentrations.Outline ethylene’s signaling pathway and explain how its regulation is unique from the other four major plant hormones. If you overexpressed CTR1 what would be the expected phenotype of a seedling in early development?There are multiple receptors encoded by genes for each of the major hormones in Arabidopsis. Give two reasons why plants have evolved multiple receptors for the same