Chapter 39: Chapter 39: Plant CommunicationPlant Communication

Plants and their EnvironmentsPlants and their Environments

Plants are living and respond to envir.Plants are living and respond to envir.

They detect light and gravity especially.They detect light and gravity especially.

Plants respond by altering growth.Plants respond by altering growth.

Receptors receive signals and initiate a Receptors receive signals and initiate a cellular response.cellular response.

–Signal Transduction PathwaySignal Transduction Pathway

–Ex: Potatoes bud in dark not lightEx: Potatoes bud in dark not light

b/c they grow in absence of light b/c they grow in absence of light (underground)(underground)

HormonesHormones Chemical Signals Chemical SignalsSent by one cell to initiate responses in Sent by one cell to initiate responses in othersothers

Can be introduced to soil or water to Can be introduced to soil or water to affect plantaffect plant

Minimal concentrations needed for big Minimal concentrations needed for big effecteffect

–Triggers a cascade response Triggers a cascade response

Relative, not absolute levels of Relative, not absolute levels of hormones regulate plant responseshormones regulate plant responses

TropismsTropismsWhole body response of plant to stimuli.Whole body response of plant to stimuli.Phototropism – Plant grows towards light.Phototropism – Plant grows towards light.Coleoptile tip must be exposed to light. If Coleoptile tip must be exposed to light. If removed or covered, no response.removed or covered, no response.Detection at coleoptile, but growth occurs Detection at coleoptile, but growth occurs further down shoot.further down shoot.–Chemical response sent from tip to Chemical response sent from tip to

shoot.shoot.Gravi-. Photo- and thigmo-tropismGravi-. Photo- and thigmo-tropism–Gravity, light, touchGravity, light, touch

PhototropismPhototropism

Plants detect the intensity, Plants detect the intensity, direction, and wavelength of light.direction, and wavelength of light.

They will bend towards the area They will bend towards the area with the best light with the best light (intensity/quality)(intensity/quality)

Phytochromes = receptorsPhytochromes = receptors

Phototropism is a Hormonal ResponsePhototropism is a Hormonal Response

Auxins – Plant Growth HormoneAuxins – Plant Growth HormoneResponsible for Responsible for tropisms.tropisms.2 Theories:2 Theories:–Auxin concentrated Auxin concentrated

on dark side of plant on dark side of plant traditional theory traditional theory

–An auxin inhibitor An auxin inhibitor concentrated on concentrated on light side of plant light side of plant

more recent more recent researchresearch

AuxinsAuxins

Main function is to promote shoot Main function is to promote shoot elongation at low concentrations elongation at low concentrations

Loosen cell wall and allow increase HLoosen cell wall and allow increase H22O O

uptake (elongation)uptake (elongation)

Also induce division in cambiumAlso induce division in cambium

Too high of a [auxin] will cause production Too high of a [auxin] will cause production of ethylene which inhibits elongationof ethylene which inhibits elongation

Causes rapid translation of proteinsCauses rapid translation of proteins

–Gene regulationGene regulation

CytokininsCytokininsInduce cytokinesis (cell division)Induce cytokinesis (cell division)Operate in balance with auxinsOperate in balance with auxins–Equal: No differentiation, just Equal: No differentiation, just

divisiondivision–More cytokinin: Shoot buds form More cytokinin: Shoot buds form –More auxin: roots formMore auxin: roots form–Auxins inhibit auxiliary growth, Auxins inhibit auxiliary growth,

cytokinins promote itcytokinins promote it–Slow agingSlow aging

GibberellinsGibberellinsProduced in roots Produced in roots and leavesand leaves

Stimulate growth of Stimulate growth of leaves and stemsleaves and stems

Elongation and Elongation and divisiondivision

Works in cooperation Works in cooperation with auxin to loosen with auxin to loosen cell walls (more Hcell walls (more H22O O

in = elongation)in = elongation)Effect of Gibberellins

Seed Dormancy and GibberellinsSeed Dormancy and Gibberellins

When conditions are appropriate, When conditions are appropriate, the release of gibberellins signals the release of gibberellins signals the seed to germinatethe seed to germinate

May stimulate digestive enzymes May stimulate digestive enzymes to mobilize stored nutrientsto mobilize stored nutrients

Abscisic Acid (ABA)Abscisic Acid (ABA)

Slows growthSlows growth

Works antagonistically against the Works antagonistically against the other growth hormones other growth hormones (gibberellins, auxins, cytokinins)(gibberellins, auxins, cytokinins)

Ratio b/t ABA and othersRatio b/t ABA and others

Seed dormancySeed dormancy

Allows plants to withstand droughts Allows plants to withstand droughts (close stomata)(close stomata)

EthyleneEthylene

Leaf abscission (fall off)Leaf abscission (fall off)

Fruit ripeningFruit ripening

Programmed cell deathProgrammed cell death

High [auxins] stimulate productionHigh [auxins] stimulate production

Involved in thigmotropism (touch)Involved in thigmotropism (touch)

ApoptosisApoptosis

ApoptosisApoptosisSystematic, preprogrammed (DNA) Systematic, preprogrammed (DNA) cell death.cell death.Enzymes break down organics (DNA, Enzymes break down organics (DNA, chlorophyll, RNA, proteins)chlorophyll, RNA, proteins)Bursts of ethylene during autumn Bursts of ethylene during autumn cause plants to lose their leaves and cause plants to lose their leaves and prepare for winter. First, they break prepare for winter. First, they break down the organic molecules.down the organic molecules.–Stored in stem parenchyma cells Stored in stem parenchyma cells

(reused by new spring leaves)(reused by new spring leaves)

Seed Dispersal Seed Dispersal Fruits FruitsWhen a bear eats a When a bear eats a piece of fruit, he eats piece of fruit, he eats the seeds. the seeds.

He doesn’t digest He doesn’t digest the seeds.the seeds.

He poops the seeds.He poops the seeds.

The poop is fertilizer The poop is fertilizer for the seeds.for the seeds.

Thanks Fozzy.Thanks Fozzy.

Ripening of FruitRipening of Fruit

Ethylene production causes Ethylene production causes ripeningripening

Storing fruits in a paper bag Storing fruits in a paper bag accelerates ripening (traps accelerates ripening (traps ethylene)ethylene)

Storing orange juice in the cabinet Storing orange juice in the cabinet accelerates ripening accelerates ripening

Circadian RhythmsCircadian Rhythms

Plants go through processes in Plants go through processes in a 24-hour (approx.) cyclea 24-hour (approx.) cycle

When isolated, they lose sync When isolated, they lose sync with the external ques and with the external ques and regain when replacedregain when replaced

Think JetlagThink Jetlag

PhotoperiodismPhotoperiodismPlant leaves monitor the relative length of Plant leaves monitor the relative length of day and nightday and nightAllows seasonal changes in plants (ie: Allows seasonal changes in plants (ie: flowering)flowering)Short-day plantsShort-day plants require light period require light period shortershorter than a critical length to flower. than a critical length to flower.Long-day plantsLong-day plants flower when the light flower when the light period is period is longerlonger than a critical number of than a critical number of hourshoursDay-neutral plantsDay-neutral plants flower at maturity, flower at maturity, regardless of day lengthregardless of day length

Short/Long Day PlantsShort/Long Day Plants

Short day = Short day = long nightlong night

Long Day = Long Day = short nightshort night

Many plants Many plants require require uninterrupted uninterrupted darkness darkness hours to hours to flowerflower

Water DeficitWater Deficit

Bright, sunny days Bright, sunny days plants can lose plants can lose more Hmore H22O than they take inO than they take in

As HAs H22O dec. the guard cells close O dec. the guard cells close

stomatastomata

Inc. ABA production (close stomata)Inc. ABA production (close stomata)

Inhibit growth of young leavesInhibit growth of young leaves

Leaves roll to dec. surface areaLeaves roll to dec. surface area

All designed to decrease transpirationAll designed to decrease transpiration

Heat/Cold StressHeat/Cold Stress

Denatures plant enzymesDenatures plant enzymes

Transpiration = evaporative coolingTranspiration = evaporative cooling

Heat shock protein = produced when Heat shock protein = produced when temp. is raised beyond thresholdtemp. is raised beyond threshold

Often bind to enzymes to prevent Often bind to enzymes to prevent denaturizationdenaturization

Extreme cold also freezes plantsExtreme cold also freezes plants

Many plants collect solutes (dec. fp)Many plants collect solutes (dec. fp)

DefenseDefenseSome “call” Some “call” other species other species to fight to fight predators offpredators off

Plants release Plants release signal signal chemicals to chemicals to alert other alert other plants of an plants of an infestation of infestation of herbivoresherbivores