Plant Regulation

Chapter 39

Plant growth

Plants respond to environmentGrowth response to abiotic factorsWater, wind & 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

Signal transduction pathway

CYTOPLASMCELLWALL

Plasma membrane

second messengers

Relay proteins andReceptor

Hormone orenvironmentalstimulus

Activationof cellularresponses

Transduction ResponseReception1 2 3

Potato plant de-etiolation (greening)

(a) Before exposure to light (b) After a week’s exposureto natural daylight

Potato response

Reception

CYTOPLASM

Plasmamembrane

Phytochromeactivatedby light

Cellwall

Light

1 Transduction

cGMP

Secondmessengerproduced

Proteinkinase 1

2

Ca2+ channelopened

Ca2+

De-etiolation(greening)responseproteins

Translation

Transcription

Transcriptionfactor 2

NUCLEUSTranscriptionfactor 1

Response3

P

P

Proteinkinase 2

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 shootsPromotes activity of vascular cambium Promotes lateral root growthFound in pollen, fruit development

Auxins

Plasticity (soften) of plantElongation of plantAuxin moves from light exposed sideTo shady sideBends towards light

Auxins

Synthetic auxinsPrevent apples from dropping earlyBerries on hollySeedless tomatoes Control weeds

Cytokinins

Similar to adenine (purines)Cell 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

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.

Ethylene

Commercially sprayed on green tomatoes Hastens ripening

Light response

Certain wavelengths of light Initiate biological changePhytochrome: Pigment containing proteinPr (inactive form)

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

Acts as switching mechanism Controls various light-induced eventsPhytochrome exposed to red light Pr is converted to Pfr

Triggering germinationFar-red light inhibits germination

Light response

Light response

Determine plant spacing Pfr plant grows tallPr plant branches

Circadian clocks

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

Gravity response

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 responseDirection of touch Object, animal, windThigmonasticResponds in one directionDespite where the contact is

Touch response

Tendril touches an object

Uneven growth

Wraps around the object

Fly trap

Touch hairs, closes (0.3 sec)

Turgor Movement

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

Turgor movement

Environmental stimuli Rapid loss of K+ out of half the pulvini cellsWater followsCauses cells to be flaccidLeaves fold in Reverses in approx 15-30 minutes

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Dormancy

Survive environment extremesSignals 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, trichomes

Plant defense

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

Plant defense

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

Plant defense

Pacific Yew produces TaxolFights cancer especially breast cancerCinchona tree bark Quinine Anti-malaria drug

Plant defenses

Toxic when metabolized by herbivore

Plant defense

Allelopathy:When a chemical secreted by roots Inhibits growth of other plantsBlack walnut trees

Plant defense

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