Plant Responses to the Environment

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Plant Responses to the Environment. Chapter 45. Plant Hormones. Hormones chemicals secreted by cells, transported to other cells where they exert effect Released in response to an environmental stimuli Promote growth, development, aging. Six Plant Hormones. Auxins Gibberellins - PowerPoint PPT Presentation


Plant Responses to the EnvironmentChapter 45 Plant HormonesHormones chemicals secreted by cells, transported to other cells where they exert effectReleased in response to an environmental stimuliPromote growth, development, agingSix Plant HormonesAuxinsGibberellinsCytokininsEthyleneAbscisic acidFlorigensAuxinsPromote or inhibit elongation in target cellsShoot high conc. causes elongationRoot low levels stimulate elongation, high conc. inhibit Synthetic auxin (2,4 D) is used to kill dicotsCommercially used to promote root formation in plant cuttings, stimulate fruit development, delay fruit fallGibberellinsPrimarily in plant shootsPromote stem elongation by increasing cell elongation and divisionStimulate bud sprouting, flowering, fruit production and development, seed germinationProduced in the shoot apical meristem, young leaves, plant embryosCytokininsPromote cell divisionSynthesized in root apical meristemInhibit formation of root branches, cause nutrients to be transported to leaves, stimulating chlorophyll production and delaying agingCommercially - sprayed on cut flowers to keep them freshEthyleneGasProduced in plant tissues, released in response to a range of environmental stimuliStress hormone produced in response to wounding, flooding, drought, extreme temp.Stimulates weak celled abscission layers - leaves, petals, fruit drop off at appropriate timesCommercially used to ripen fruitAbscisic AcidSynthesized in tissues throughout the plantHelps plants to withstand unfavorable environmental conditionsCauses stomata to close when water is scarcePromotes root growth, inhibits stem growth in dry conditions.Helps maintain dormancyFlorigensSynthesized in leavesControl flowering in response to environmentDiscovered in 2007Hormones regulate plant life cyclesHormones are produced in response to an environmental stimulusThese hormones may influence the activity of genes (activate, repress)Maintaining Dormancy of SeedsIn temperate zones, seeds remain dormant until springCold weather reduces abscisic acid, preparing plant for spring germinationIn desert plants, some seeds have high levels of abscisic acid in their coats. It may be washed away by rainGrasslands, chaparral, forest require fire for germination Gibberellin Stimulates Germination-Abscisic acid and +Gibberellin = germinationGibberellin is produced by the embryoEnzymes break down starch for energyAuxin controls OrientationLight and gravity help the seedling figure which way is upAuxin controls phototrophism growth towards light, in shootsGravitropism growth to/away from gravity, in shoots and rootsGravirtopism and phototrophism work together to cause shoot to grow upwardAuxin mediates GravitropismVertical stem auxin distributed evenlyHorizontal stem position detected and auxin distributed to lower side of stem. Lower cells elongate, bending stem upwards (-gravitropism)When stem is vertical auxin is evenly distributedAuxin from the shoot tip travels down and collects in the root tipAuxin, produced in the shoot tip, is distributed evenly across the shoot and root as it travels downwardrootseedshoot(a) The shoot and root are orientedverticallyGravitropismAuxin is transported to the lower side of theshoot, where it stimulates cell elongationand causes the stem to bend upwardAuxin is transported to the lower side of theroot, where it inhibits cell elongation andcauses the root to bend downward(b) The shoot and root are orientedhorizontallyGravitropismNegative Gravitropism Positive Gravitropism Auxin mediates Phototropism Auxin accumulates in the side of the shoot that is away from the light.Cells elongate and bend towards the lightAnimation: Hormone CharacteristicsAnimation: Hormone Transport and ActivityAuxin mediates Root ElongationToward gravityIf root is horizontal, they sense gravity and cause auxin transport to lower sideLower side cells elongate, causing root to grow towards gravityHow do they sense gravity? Statoliths starch filled plastids settle into the lower part of the cellStatoliths May Be Gravity Detectors rootstatolithsnucleuscell inroot capPlant responds to EnvironmentWhen shoot or root push against soil, ethylene is given off.Elongation slows and cells become thicker and strongerMore able to force their way through soilDicots ethylene causes formation of hook in forming shoot ThimotropismDirectional movement or growth in response to touchCell elongation on contact side is inhibited, tendrils growEtheylene may be produced by cells touching the objectShoot and Root BranchingControlled by Auxin and CytokininGrowth of shoot must be balanced by root growthWater, mineral, anchorage of plantStems auxin inhibits later bud growth to form branches, cytokinin promotes this growthRoot cytokinin stimulates root branching, auxin promotes this growthApical DominancePinching back the tip of a plant causes bushy growth because apical meristems release auxin which suppresses bud development into branches.Lateral bud sproutingAuxin is transported from the stem to the root, decreasing in concentration.Cytokinin is transported from the root to the stem, decreasing in concentration.Lateral buds closes to shoot receive enough auxin to inhibit growth, very little cytokinin = remain dormantLower lateral buds receive less auxin and more cytokinin = stimulate to grow into branchesRoot branch formationAuxin, transported down from the stem stimulates branch roots to formCytokinin produced in the root apical meristem inhibits root branching and is transported from the root towards the shootRoots closer to the shoot develop branch rootsGradient of hormones keeps size of root and shoot in balanceLateral buds are inhibited by high auxin levelsBranch roots develop (optimal ratio of cytokinin to auxin)Branch roots are inhibited by high cytokinin levelsLateral buds develop into branches (optimal ratio of auxin to cytokinin)auxincytokininhighhighshoot tiproot tipGradient of Auxin and CytokininResponse to Light and DarkTiming of flowering and seed production is crucialEnvironmental clues like water and temperature are unpredictableDay length is very reliableShortening vs. lengthening days Its about the amount of darknessDay-neutral plants flower independently of day length Roses, tomatoes, cucumbers, cornLong-day plants flower when uninterrupted dark is shorter than species-specific durationIris, lettuce, spinach, hollyhocksShort-day plants flower when uninterrupted dark is longer than species-specific durationCockleburs, chrysanthemums, asters, potato, goldenrodIt is really more about the amount of darkness than lightlong nightshort nightnightdayinterrupted nightlong-day plant (iris)short-day plant (chrysanthemum)day-neutral plant (rose)The Effects of Darkness on Flowering Phytochrome Plants measure darkness using a biological clock that isnt well understoodEach time the phytochrome molecule is exposed to light, the clock resets to 0If a plant needs 8 hours of dark to flower but is interrupted with a flash of light at 4 hours, the clock will resetLight changes the shape of the phytochrome moleculeconversion in lightabsorbsred lightPr(inactive)Pfr(active)Pfr stimulates or inhibits aresponseconversion in darkabsorbsfar-red lightboth forms are present in daylightThe Light-Sensitive Phytochrome Pigment Author Animation: PhytochromeAuthor Animation: Morning GloryAnimation: Seedling ElongationFlorigen Stimulates FloweringLeaves produce florigen in response to the biological clockTransported on phloem to the apical meristem where it activates genes that are responsible for floweringCoordination of Seeds and FruitAuxin and gibberellin promote growth of ovaryApply to fruit and they grow larger and looserEthylene Unripe fruit is green, bitterRipened fruit turns color & attracts animalsEthylene gas stimulates ripening, as they ripen fruits give off ethylene gas to stimulate ripening of adjacent fruit Bananas & tomatoes are picked & shipped greenSenscenceGenetically programmed series of events that prepare the plant for winterEthylene production increasesAuxin and cytokinin production decreasesStarches and chlorophyll are broken down and stored in the stem and rootsThe Abscission Layer A layer located where the fruit or leaf join the stemEthylene promotes breakdown of this layerLeaves/fruit drop at correct timeCan also be triggered by stressPlant CommunicationPlants summon insect bodyguardsWhen attacked by caterpillars, corn releases chemicals, stimulated by volicitin (in caterpillar saliva)Parasitic wasps are attracted to chemical, lay eggs in caterpillarLima beans, attacked by spider mites release chemical that attracts carnivorous mite that preys on spider mite A caterpillar chews on a corn leaf, leaving traces of saliva that contains volicitin1 Volicitin and leaf damage cause the plant to synthesize and release volatile chemicals2 The wasps lay their eggs on the caterpillar, which will provide food for their larvae4 The released chemicals attract female parasitic wasps3A Chemical Cry for Help Animation: Chemical MessengersPlant DefenseSome plants, when damaged by insects, produce a signaling molecule that moves through the plant. The plant then makes a distasteful chemicalRadishes and caterpillarsWarning the NeighborsHealthy plants sense chemicals released by neighbors that have been wounded by insects.Salicylic acid methyl salicylate (volitile)Neighbors boost their defensesMimosaThigmotropism - sensitive to touchStimulated by electric signals conducted through motor cells at the base of each leafCarnivorous PlantsSundew - movement of trapped insects triggers thigmotropism in the hairs, secrete sticky goop, smothering the insectBladderwort trapdoor is sprung by insect, opens inward suddenly, sucking insect into the bladder where it is digested.A Sundew and Its Insect Prey The Bladderwort Snares Tiny Aquatic Organisms Author Animation: Venus Fly Trap


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