Plant Regulation

Chapter 39

Plant growth

Plants respond to environmentGrowth response to abiotic factorsWater, wind and light

Plant responses

LightGravityTouchWater Temperature

Plant hormones

Internal signal (developmental)Environmental signalChemical binds receptorPhysiological responseDevelopmental responseReception-transduction-responseRegulate growth & developmentNew protein or activation of protein

Light response

Photomorphogenesis:Nondirectional light-triggered developmentChange in formFlower formationPhototropisms:Directional developmentTrope (turn)

Plant hormones

AuxinCytokininsGibberellinsBrassinosteriodsEthyleneAbscisic acid

Auxin

First plant hormone(IAA) Indoleacetic acidFound in apical meristems of shootsPlasticity (soften) of plantElongation of plant

Auxins

Auxin moves from light exposed sideTo the shady sidePromotes growth & elongationHelps plants response to environmentPromotes activity of vascular cambium Promotes lateral root growthFound in pollen, fruit development

Auxins

Synthetic auxinsPrevent apples from dropping earlyBerries on hollySeedless tomatoes (green house tomatoes)Control weeds (higher dose, prevents axial growth)

Cytokinins

PurinesSimilar structure to adenineCell division & differentiationFound in root apical meristems Transported through plantLateral buds into branchesInhibit lateral roots (auxin promotes)

Cytokinins

Remove terminal bud Plant becomes bushierPromotes lateral buds into branchesAuxin on cut surface Inhibits lateral buds

Cytokinins

Applied to cut leaves prevent agingFlorists spray on fresh cut flowersCrown gallTumor growth on treesBacteria causes increased production of auxin & cytokinins

Gibberellins

Stem elongationEnhances if auxin presentFound in apical portions of stems & rootsApply to dwarf plants restores normal growth

Gibberellins

Stimulate enzymes that utilize food during germinationHastens germinationFruit developmentHelps space grape leaves (internodes)Fruits have more space to grow

Brassinosteriods

Similar in structure to testosterone, estradiol, cortisolElongation & cell divisionBending of stemsReproductive developmentDelays senescence

Abscisic Acid

Found in mature green leaves, fruit & root capsFormation of winter budsInduce seed dormancyControls stomata open/close

Ethylene

GasSuppresses stem & root elongationHastens fruit ripening Response to stressLeaf abscissionProgrammed cell death

Ethylene

Mechanical stress on stem tip.Triple response Enables a seedling to avoid an obstacle.Stem elongation slows, Stem thickens, Curvature causes the stem to start growing horizontally.

Ethylene

Commercially sprayed on green tomatoes Hastens ripening

Light response

Certain wavelengths of light Initiate biological changePhytochrome: Pigment containing proteinTwo forms Pr (inactive form) and Pfr(active form)

Light response

Inter-convertible formsPr absorbs red light (660nm)Converts to the active form Pfr

Pfr absorbs far red light (730 nm)Converts to the inactive form Pr

Light response

Inter-conversion acts as switching mechanism Controls various light-induced eventsPfr form triggers plant’s developmental responses to light.Exposure to far-red light inhibits the germination response.

Light response

Light response

Seeds exposed to sunlightPhytochrome exposed to red light Pr is converted to Pfr

Triggering germination.

Light response

Determine spacing between plants Pfr plant grows tallPr plant branches

Circadian clocks

GravitropismResponse of plant to gravitational pullShoot negative gravitropic responseRoots positive gravitropic response

Gravity response

Gravity response

Response present at germinationStemGreater concentration of a elongation hormone on the under sideCells grow more then upper sideRoot Upper cells grow more rapidly Root grows down

Gravity response

Amyloplasts:Starch containing organellesMaybe involved in sensing gravityStem located in the endoplasmRoot located in the root capRoot cap is involved in sensing gravity

Touch response

ThigmotropismDirectional growth responseIn direction of touch Object, animal, windThigmonasticResponds in one direction despite where the contact is

Touch response

Tendril touches an object

Uneven growth

Wraps around the object

Fly trap

Touch hairs, closes (0.3 sec)

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Turgor Movement

Touch induces change in turgorCells collapseCauses leaf movementPulvini:Multicellular swellings at the base of the leaf or leaflet

Turgor movement

Stimuli such as wind, touch, heatRapid loss of K+ out of half the pulvini cellsWater followsCauses cells to be flaccidLeaves fold in MimosaReverses in approx 15-30 minutes

Dormancy

Survive environment extremesPlant have a dormant stageTemperature, light & water Signals that initiate or terminate dormancyTemperate regions dormancy occurs during winter (day-length)Dry climates dormancy comes in summer (rainfall)

Plant defense

First defense Dermal tissue systemCutin, suberinBark, thorns, trichomesNematodes, fungi, bugs still penetrate these defenses

Plant defense

PoisonsCyanide-containing compoundsStops electron-transport Cassava (African food)Secondary metabolitesAlkaloids (caffeine, nicotine, cocaine, and morphine)

Secondary metabolites

Soy products produce PhytoestrogensSimilar in structure to human estrogenDecreased prostate cancer in Asian menHelp minimize menopausal symptoms

Secondary metabolites

Pacific Yew produces TaxolHelps fight cancer especially breast cancerCinchona tree bark Quinine Anti-malaria drugDesigned to harm herbivores

Plant defenses

1. Toxin in membrane-bound structure2. Poison toxic when metabolized by herbivore

Allelopathy

Chemical secreted by roots of one plant Inhibits growth of other plantsBlack walnut trees

Plant response

Plant is injuredCell death at locationPrevents further spread of pathogenH2O2 & NO can be produced

Can cause harm to invaderChemicals released to warn other plants of an invasion

Wasps