CHAPTER 8CHAPTER 8

PLANT HORMONES PLANT HORMONES Biochemistry and Biochemistry and

MetabolismMetabolism

Plants Hormones :Plants Hormones :

Means intercellular comunication within plants is mediated by Means intercellular comunication within plants is mediated by the action of chemical messengersthe action of chemical messengers

Signal molecules that individually or cooperatively direct the Signal molecules that individually or cooperatively direct the development of individual cells, development of individual cells,

or /@or /@

Carry information between cells and thus coordinate growth Carry information between cells and thus coordinate growth and developmentand development

Naturally occurring organic substances that at low Naturally occurring organic substances that at low concentration will influence physiological processconcentration will influence physiological process

Site of synthesis not clearly localizedSite of synthesis not clearly localized

More diffuse, cannot always localized to discrete organsMore diffuse, cannot always localized to discrete organs

Types of plant hormones Types of plant hormones

5 recognized groups of plant hormones :5 recognized groups of plant hormones :

Auxins; Gibberellins; Cytokinins; Abscisic Auxins; Gibberellins; Cytokinins; Abscisic acid; and Ethyleneacid; and Ethylene

More recently a 6 groups :More recently a 6 groups :

Brassinosteroids; Polyamines; Jasmonic acid; Brassinosteroids; Polyamines; Jasmonic acid; and Salicylic acidand Salicylic acid

(i) AUXIN(i) AUXIN

First plant hormone to be discoveredFirst plant hormone to be discovered Play a major role :Play a major role :

i. in the regulation of plant cell elongationi. in the regulation of plant cell elongation

ii. in the growth responses of plants to ii. in the growth responses of plants to

undirectional stimulus, it known as tropismundirectional stimulus, it known as tropism

Natural auxins :Natural auxins : Indole-3-acetic acid (IAA) Indole-3-acetic acid (IAA) 4-chloroindole-3-acetic asid 4-chloroindole-3-acetic asid Phenylacetic acidPhenylacetic acid Indole-3-butyric acid (IBA)Indole-3-butyric acid (IBA)

Synthetic auxins:Synthetic auxins: Naphthaleneacetic acid (NAA) Naphthaleneacetic acid (NAA) 2-Methoxy-3,6-dichloro-benzoic acid (dicamba)2-Methoxy-3,6-dichloro-benzoic acid (dicamba) 2,4-Dichlorophenoxyacetic acid (2,4-D)2,4-Dichlorophenoxyacetic acid (2,4-D) 2,4,5-Trichlorophenoxy-acetic acid (2,4,5-T)2,4,5-Trichlorophenoxy-acetic acid (2,4,5-T) Amount of IAA present depend on a number of Amount of IAA present depend on a number of

factors :factors :

(i) Type of tissue(i) Type of tissue (ii) Age of tissues(ii) Age of tissues (iii) Stage of growth(iii) Stage of growth Concentrations exceeding the optimum Concentrations exceeding the optimum characteristically result in reduced growthcharacteristically result in reduced growth

Auxin concentration is high enough Auxin concentration is high enough ⇨⇨ growth growth inhibited compared with controlinhibited compared with control

Exogenous hormone Exogenous hormone ⇨⇨ do not show a do not show a significant responsesignificant response

Endogenous hormone Endogenous hormone ⇨⇨ content at intact content at intact tissues enough to support elongationtissues enough to support elongation

Effect of exogenous supplied auxin only in Effect of exogenous supplied auxin only in tissues that have been removed from the tissues that have been removed from the auxin supply (such as excised segments of auxin supply (such as excised segments of stem and coleoptile)stem and coleoptile)

Auxins : Chemistry, Metabolic and Auxins : Chemistry, Metabolic and TransportTransport 1870s ; Darwin and son Francis studies plant 1870s ; Darwin and son Francis studies plant

growth phenomena of the growth stimulus in growth phenomena of the growth stimulus in Avena Avena sativasativa (oat) coleoptile (oat) coleoptile

Auxin regulated cell enlargement in excised tissues Auxin regulated cell enlargement in excised tissues such as coleoptilesuch as coleoptile

If the tip of a coleoptile removed If the tip of a coleoptile removed ⇨⇨ coleoptile coleoptile growth ceased. They found that the tip of the growth ceased. They found that the tip of the coleoptile preceived lightcoleoptile preceived light

If their covered the tips If their covered the tips With metal – No growth toward lightWith metal – No growth toward light With glass – Growing towards lightWith glass – Growing towards light # coleoptile growth towards light is controlled by # coleoptile growth towards light is controlled by

coleoptile tip coleoptile tip

Went’s discovery :Went’s discovery :Growth promoting substance from excised coleoptile Growth promoting substance from excised coleoptile tips would diffuse into agar blocktips would diffuse into agar block

Blocks could the used to restore growth in Blocks could the used to restore growth in decapitated coleoptiledecapitated coleoptile

If agar block containing auxin was placed on one If agar block containing auxin was placed on one side of coleoptile stump side of coleoptile stump ⇨⇨ coleoptile bent away from coleoptile bent away from the side containing the blockthe side containing the block

Curvature occurred because:Curvature occurred because: i. the increase in auxin on one side stimulated cell i. the increase in auxin on one side stimulated cell

elongation; and elongation; and ii. decrease in auxin on the other side caused a ii. decrease in auxin on the other side caused a descrease in the growth ratedescrease in the growth rate

Refer to fig 16.1 page 400 (Taiz /Zieger)- Plant Refer to fig 16.1 page 400 (Taiz /Zieger)- Plant PhysiologyPhysiology

Transport of auxinsTransport of auxins Depend on the developmental stage of Depend on the developmental stage of

theorgan/tissue of planttheorgan/tissue of plant

Transport of hormone into or out of tissue/organ Transport of hormone into or out of tissue/organ influence level of active hormone within influence level of active hormone within tissue/organtissue/organ

Hormone (Auxin) transport of plant is the polarity Hormone (Auxin) transport of plant is the polarity of movementof movement

Polar transport expressed as movement in one Polar transport expressed as movement in one directiondirection

This indicate that polarity is not driven by external This indicate that polarity is not driven by external forces (gravity etc.) but the property of cells forces (gravity etc.) but the property of cells themselvesthemselves

When movement is preferentially away from the When movement is preferentially away from the morphological apex toward the morphological morphological apex toward the morphological base of the transporting tissue, the direction of base of the transporting tissue, the direction of movement described as movement described as basipetalbasipetal

Movement in the opposite direction, that it toward Movement in the opposite direction, that it toward the morphological apex referred as the morphological apex referred as acropetalacropetal

When stem or coleoptile is inverted, original When stem or coleoptile is inverted, original direction is maintaineddirection is maintained

# Refer to Fig 16.7 page 349 textbook# Refer to Fig 16.7 page 349 textbook

14C-IAA 14C-IAA

14C-IAA14C-IAA

A

B

B

A

A

A

A

B

B

B

Normal orientation

Inverted sections

Receiver block

Donor block

Fig. 16.7 Polarity in auxin transport in Avena sativa coleoptile segment

Auxin has a variety of effect s on plant growth and Auxin has a variety of effect s on plant growth and morphogenesis such as :morphogenesis such as :

promote the elongation growth of stem and coleoptile promote the elongation growth of stem and coleoptile (however, it inhibit root elongation)(however, it inhibit root elongation)

promote cell division in stems (but inhibit in lateral buds)promote cell division in stems (but inhibit in lateral buds) Development of fruitDevelopment of fruit

Effect of auxin depend of factor, including Effect of auxin depend of factor, including (i) developmental stage of tissue or organ(i) developmental stage of tissue or organ(ii) concentration of auxin(ii) concentration of auxin(iii) type of auxin (natural @ synthetic)(iii) type of auxin (natural @ synthetic)(iv) involvement of other plant hormones(iv) involvement of other plant hormones(v) use of intact versus excised tissue for (v) use of intact versus excised tissue for experimentexperiment

Physiologial Effects of AuxinPhysiologial Effects of Auxin

1. Cell elongation/enlargement1. Cell elongation/enlargement

Stimulate cell elongation in excised tissue Stimulate cell elongation in excised tissue (coleoptile)(coleoptile)

Auxin concentration response curve show Auxin concentration response curve show increasing response with increasing increasing response with increasing concentration of auxin an optimum concentration of auxin an optimum concentration is reachedconcentration is reached

Concentration exceeding the optimum Concentration exceeding the optimum ⇨⇨ rduced growthrduced growth

Concentration high Concentration high ⇨⇨ growth inhibited growth inhibited

2. Increases the extensibility of 2. Increases the extensibility of the cell wallthe cell wall

Increase in cell wall extensibility in coleoptile and young Increase in cell wall extensibility in coleoptile and young developing stemdeveloping stem

Auxin acts at the plasma membrane @ within the cell Auxin acts at the plasma membrane @ within the cell Acid growth hypothesis proposed that auxin activates ATP-Acid growth hypothesis proposed that auxin activates ATP-

proton pump located in plasma membrane.proton pump located in plasma membrane. Acid-growth hypothesis to explains auxin stimulated plant Acid-growth hypothesis to explains auxin stimulated plant

cell elongation and enlargementcell elongation and enlargement According to the hypothesis, auxin causes responsive cells According to the hypothesis, auxin causes responsive cells

to extrude proton (Hto extrude proton (H++)actively into the cell wall regions )actively into the cell wall regions ⇨⇨ decrease pH activates wall-loosening enzymes that promote decrease pH activates wall-loosening enzymes that promote the breakage of cell wall bond the breakage of cell wall bond ⇨⇨ increase wall extensibility increase wall extensibility

3. Growth responses to 3. Growth responses to directional stimulidirectional stimuli Auxin mediate effect of light and gravity on plant Auxin mediate effect of light and gravity on plant

growthgrowth Plant oriented to the environment Plant oriented to the environment ⇨⇨ leaves leaves

(houseplant) facing to window; roots growing (houseplant) facing to window; roots growing toward the earthtoward the earth

Tropic responses i.e. growth in response to Tropic responses i.e. growth in response to directional light directional light ⇨⇨ phototropism or gravity phototropism or gravity ⇨⇨ gravitropismgravitropism

Toward light Toward light ⇨⇨ +ve phototropism +ve phototropism Away from light Away from light ⇨⇨-ve phototropism-ve phototropism

4. Inhibits the growth of lateral 4. Inhibits the growth of lateral buds buds @ Apical Dominance@ Apical Dominance

Removal of shoot apex, stimulate growth one Removal of shoot apex, stimulate growth one @ more lateral bud @ more lateral bud

Auxin from apical bud inhibits growth of Auxin from apical bud inhibits growth of lateral (axillary) budlateral (axillary) bud

5. Promote the formation of 5. Promote the formation of lateral rootslateral roots

Elongation growth of root inhibited by auxin, but Elongation growth of root inhibited by auxin, but initial of lateral (branch) root and adventitious initial of lateral (branch) root and adventitious root is stimulated by high auxin levelroot is stimulated by high auxin level

The dividing cell by auxin form a root apex and The dividing cell by auxin form a root apex and lateral root grow through root cortex and lateral root grow through root cortex and epidermisepidermis

Adventitious root develop from a part of the Adventitious root develop from a part of the plant @ other than the normal form of root plant @ other than the normal form of root branchingbranching

6. Delay the onset of leaf 6. Delay the onset of leaf abscissionabscission Process of shedding organs such as leaves, flower and Process of shedding organs such as leaves, flower and

fruit; known as abscissionfruit; known as abscission Abscission occurs in region called abscission zone; Abscission occurs in region called abscission zone;

located near the base petiole.located near the base petiole. Organ ages Organ ages ⇨⇨ cell wall in abscission layer weaken and cell wall in abscission layer weaken and

separateseparate Leaf aging called leaf senescence. The cell wall in Leaf aging called leaf senescence. The cell wall in

abscission layer digested which cause them to become abscission layer digested which cause them to become soft and weak soft and weak

The leaf break off at the abscission layer due to stressThe leaf break off at the abscission layer due to stress Abscission dependent on concentration of auxin on either Abscission dependent on concentration of auxin on either

side of the abscission layerside of the abscission layer As leaf ages release of auxins decline, inducing the As leaf ages release of auxins decline, inducing the

ethylene synthesis ethylene synthesis ⇨⇨ abscission stimulated abscission stimulated

Environmental stress eg. Water stress, nutrient deficiency reduce IAA

Ethylene produced at the abscission layer

Cell wall expand and suberized

cellulase & pectinase are produced

Middle lamela degraded

Cells separated, leaves/fruits shedd

Abscission layer

senescence

7. Regulates fruit 7. Regulates fruit developmentdevelopment Auxin produced in pollen, endosperm and Auxin produced in pollen, endosperm and

embryo of developing seedsembryo of developing seeds

Involve in the initial stimulus for fruit growth from Involve in the initial stimulus for fruit growth from pollinationpollination

After fertilization, fruit growth depend on auxin After fertilization, fruit growth depend on auxin produced in developing seedproduced in developing seed

In some species In some species ⇨⇨seedless fruits produced seedless fruits produced naturally @ by treating the unpollinated flower naturally @ by treating the unpollinated flower with auxin called parthenocarpywith auxin called parthenocarpy

Ethylene known to influence fruit developmentEthylene known to influence fruit development

The effect of auxin on fruiting mediated through The effect of auxin on fruiting mediated through the promotion of ethylene synthesisthe promotion of ethylene synthesis

Gibberellins members of terpenoidsGibberellins members of terpenoids Gibberellins; assigned as GAGibberellins; assigned as GA

most important in higher plantsmost important in higher plants

GAGA33 extracted from fungal culture extracted from fungal culture

3 principal sites of gibberellin biosynthesis :3 principal sites of gibberellin biosynthesis :

(i) Developing seeds (developing endosperm, (i) Developing seeds (developing endosperm, cotyledon, scutellum)cotyledon, scutellum)

(ii) Developing fruits (ii) Developing fruits

(iii) Young leaves of developing apical bud and (iii) Young leaves of developing apical bud and elongating elongating

shootsshoots

(iv) Apical region of root(iv) Apical region of root

GIBBERELLINSGIBBERELLINS

1.Stimulate hyperelongation of 1.Stimulate hyperelongation of intact stemsintact stems

Occurs especially in dwarf and rosette plants Occurs especially in dwarf and rosette plants Promote elongation in intact plants rather than Promote elongation in intact plants rather than

excised tissuesexcised tissues Study on dwarf mutants of Study on dwarf mutants of Oryza sativaOryza sativa, , Zea Zea

mays, Phaseolus vulgarismays, Phaseolus vulgaris These mutants exhibit the normal phenotype These mutants exhibit the normal phenotype

when treated with GAwhen treated with GA33

GA treated enhanced internode elongationGA treated enhanced internode elongation

PHYSIOLOGICAL ACTION OFGIBERELLINS

The role of gibberellin in stem elongation come The role of gibberellin in stem elongation come from the study of rosette plantsfrom the study of rosette plants

Rosette plants Rosette plants ⇨⇨ compact growth habit, closely compact growth habit, closely spaced leavesspaced leaves

Failure of internode elongation may result from a Failure of internode elongation may result from a genetic mutation @ environmentally inducedgenetic mutation @ environmentally induced

Environmentally limited rosette plant (egEnvironmentally limited rosette plant (eg. Brassica . Brassica spsp. and . and Spinacea oleraceaeSpinacea oleraceae) generally do not ) generally do not flower in the rosette formflower in the rosette form

Before flowering, plants undergo extensively Before flowering, plants undergo extensively internode elongation; known as bolting internode elongation; known as bolting

Bolting, due to environmental signal eg. Bolting, due to environmental signal eg. photoperiod or low temperaturephotoperiod or low temperature

Bolting in rosette plants can be induced by Bolting in rosette plants can be induced by exogenous application of GAexogenous application of GA

2. Seed germination2. Seed germination

Cereal grain seeds like Cereal grain seeds like Hordeum vulgareHordeum vulgare consists of embryo and non embryonic consists of embryo and non embryonic regionsregions

Embryo region synthesized GA and induced Embryo region synthesized GA and induced release of α-amylase to hydrolyze endosperm release of α-amylase to hydrolyze endosperm (starch)(starch)

Non embryonic region if treated with GA will Non embryonic region if treated with GA will stimulate to produce α-amylase at high stimulate to produce α-amylase at high concentration concentration

3. Stimulate mobilization of 3. Stimulate mobilization of nutrient nutrient reserve during germination reserve during germination Occurs of cereal grainOccurs of cereal grain

During imbibition water is absorbed by seed to During imbibition water is absorbed by seed to ensure GA secretionensure GA secretion

GA moves from the embryo to the aleurone where GA moves from the embryo to the aleurone where stimulated stimulated -amylase secretion (-amylase secretion (-amylase -amylase synthesized) and synthesis protease enzymesynthesized) and synthesis protease enzyme

Aleurone Aleurone ⇨⇨ a layer of cell surrounding the a layer of cell surrounding the endosperm in seedendosperm in seed

Protease converts an inactive Protease converts an inactive -amylase to the -amylase to the active form active form

-amylase and -amylase and -amylase together digest starch to -amylase together digest starch to glucose glucose ⇨⇨ which mobilized to meet the metabolic which mobilized to meet the metabolic demands of the growing embryodemands of the growing embryo

GA

protease

-amylase (inactive)

-amylase (active)

-amylase starch

glucose

aleurone

endosperm

scutellum

coleoptile

plumule embryo

radical

4. Flowering4. Flowering

Flowering is induced by gibberellinsFlowering is induced by gibberellins Eg. Eg. Pharbitis nil, Chenopodium rubrumPharbitis nil, Chenopodium rubrum will will

flower immediately flower immediately Many perennial plants capable of flowering Many perennial plants capable of flowering

after pass through a juvenile phaseafter pass through a juvenile phase Gibberellins overcome juvenile phase in Gibberellins overcome juvenile phase in

many conifers and stimulate precocious many conifers and stimulate precocious floweringflowering

Gibberellins promote maleness in unisexual Gibberellins promote maleness in unisexual flowers while auxin promote femalenessflowers while auxin promote femaleness

5. Inhibition of gibberellins 5. Inhibition of gibberellins biosynthesisbiosynthesis

Growth of stem can be inhibited or reduced by synthetic Growth of stem can be inhibited or reduced by synthetic chemical that block gibberellin biosynthesis i.e growth chemical that block gibberellin biosynthesis i.e growth retardant or anti gibberellins (AMO-1618, cycocel, retardant or anti gibberellins (AMO-1618, cycocel, Phosphan-D, ancymidol)Phosphan-D, ancymidol)

These compound has commercial application in These compound has commercial application in production of ornamental plantsproduction of ornamental plants

Effects:Effects: ⇨⇨ To reduce stem elongationTo reduce stem elongation ⇨⇨ Results in shorter and compact plants with darker Results in shorter and compact plants with darker green foliagegreen foliage Spraying the plant (Wheat) with antigibberellin produce a Spraying the plant (Wheat) with antigibberellin produce a

shorter, stiffer stem and preventing lodgingshorter, stiffer stem and preventing lodging

Cytokinin- adenine derivativesCytokinin- adenine derivatives Kinetin- first compound found with cytokinin Kinetin- first compound found with cytokinin

activityactivity Synthetic cytokinin prepared by heating DNASynthetic cytokinin prepared by heating DNA Zeatin- first natural cytokinin discovered and Zeatin- first natural cytokinin discovered and

most widespreadmost widespread Isopentenyl adenine (iP)Isopentenyl adenine (iP) Dihydrozeatin (diHZ) : leass active than Dihydrozeatin (diHZ) : leass active than

zeatinzeatin Benzyl adenine (BAP)Benzyl adenine (BAP)

CYTOKININS

11..Cytokinins regulate cell Cytokinins regulate cell divisiondivision

Cytokinin is major factor in regulating cell Cytokinin is major factor in regulating cell division in the presence of auxindivision in the presence of auxin

Have capacity to initiate division in plant Have capacity to initiate division in plant cells and in quiescent or non dividing cells cells and in quiescent or non dividing cells (tissue culture)(tissue culture)

Initiate cell division by controlling cell cycle Initiate cell division by controlling cell cycle at two pointsat two points

1. Catalyze transition from G2 phase to 1. Catalyze transition from G2 phase to mitosismitosis

2. Control G1 to S phase transition2. Control G1 to S phase transition

2. Stimulate cell proliferation2. Stimulate cell proliferation

In the case of neoplastic (tumorous growth)In the case of neoplastic (tumorous growth) Bacterium Bacterium Agrobacterium tumefaciens Agrobacterium tumefaciens pathogens pathogens

that causes tumorous growth on stems known: that causes tumorous growth on stems known: crown gallcrown gall

Crown gall tissue can be excised and maintained Crown gall tissue can be excised and maintained on simple medium without hormoneon simple medium without hormone

Have capacity to synthesis auxin and cytokininHave capacity to synthesis auxin and cytokinin When bacteria invade host tissue, it transfer these When bacteria invade host tissue, it transfer these

genes genes Genes replicated in host cellGenes replicated in host cell Produced elevated level of auxin and cytokinin Produced elevated level of auxin and cytokinin Stimulate neoplastic growthStimulate neoplastic growth

Crown gallCrown gall

2. Organogenesis2. Organogenesis Cytokinin and auxin stimulate organogenesis: Cytokinin and auxin stimulate organogenesis:

organ formationorgan formation Development of shoot and rootDevelopment of shoot and root Cell culture growth required cytokinin and Cell culture growth required cytokinin and

auxinauxin High Cytokinin/auxin ration stimulate root High Cytokinin/auxin ration stimulate root

formationformation Low cytokinin/auxin ration stimulate shoot Low cytokinin/auxin ration stimulate shoot

formation formation

3. Senescence3. Senescence Mature leaves and fruits express senescenceMature leaves and fruits express senescence Senescence: breakdown of protein, nucleic acids, Senescence: breakdown of protein, nucleic acids,

other macromolecules, loss of chlorophyll, other macromolecules, loss of chlorophyll, accumulation of amino acids accumulation of amino acids

Cytokinins will delay senescence while ethylene Cytokinins will delay senescence while ethylene promote senescencepromote senescence

Cytokinins direct nutrient mobilization and retention Cytokinins direct nutrient mobilization and retention by stimulating metabolism in the area of applicationby stimulating metabolism in the area of application

Creates a new sink: area that attract metabolites Creates a new sink: area that attract metabolites from region of applicationfrom region of application

senescence

Radioactive spreads into vascular tissue for export through

petiole

Radioactive accumulates in the area treated with

kinetin

kinetin kinetin

Control Treatment with cytokinins

radioactive

Radioactive retain near point of

application

Experiment : role of cytokinins Experiment : role of cytokinins in nutrient mobilizationin nutrient mobilization

A B

C

-Radioactive labeled nutrient are fed to the plant-In control (A) radioactive spreads into vascular tissue for export through petiole

-In treatment (B) one part/half of leaf is treated with cytokinin-Radioactive accumulates in the area treated with kinetin -In other treatment (C) cytokinin applied on part of leaf (right)-Radioactive retain near point of application

-Cytokinins direct nutrient mobilization and retention by stimulating metabolism in the area of application-creates a new sink area that attract metabolites from region of application

Stimulate cell enlargement Stimulate cell enlargement Regulate vascular differentiaitonRegulate vascular differentiaitonPromote axillary bud and release apical Promote axillary bud and release apical

dominance dominance

Other effects of cytokininsOther effects of cytokinins

Abscisic acid is a single compoundAbscisic acid is a single compound Occur in mature, green leavesOccur in mature, green leaves Synthesized in cytoplasm of leaf mesophyll cell Synthesized in cytoplasm of leaf mesophyll cell

and accumulated in chloroplastand accumulated in chloroplast Able to move quickly out of leaves sink tissuesAble to move quickly out of leaves sink tissues Actions: induce storage protein synthesis during Actions: induce storage protein synthesis during

seed developmentseed development Regulating stomatal closure during water stressRegulating stomatal closure during water stress Also involved in regulating abscission and bud Also involved in regulating abscission and bud

dormancydormancy

Abscisic AcidAbscisic Acid

In drought, leaves will synthesized high level of In drought, leaves will synthesized high level of ABA ABA

Allowed stomata closureAllowed stomata closure Water will be stored during drought/Water will be stored during drought/waterwater stress stress

2. Bud/seed dormancy2. Bud/seed dormancy Woody plants in temperate zoneWoody plants in temperate zone ABA concentration maximum in early winter and ABA concentration maximum in early winter and

low end of winterlow end of winter ABA prevents bud development and seed ABA prevents bud development and seed

germinationgermination

1. Stomatal closure1. Stomatal closure

ABA physiological effects

ABA actions antagonistic with other hormone: ABA actions antagonistic with other hormone: Inhibits amilase which produced by seed treated Inhibits amilase which produced by seed treated

with giberellins with giberellins Promote chlorosis which have been inhibited by Promote chlorosis which have been inhibited by

cytokininscytokinins Inhibits cell wall elasticity and cell enlargement Inhibits cell wall elasticity and cell enlargement

by IAAby IAA

Simple hydrocarbon gaseous : H2C=CH2Simple hydrocarbon gaseous : H2C=CH2 Not required for normal vegetative growthNot required for normal vegetative growth Synthesized primarily in response to stress Synthesized primarily in response to stress Produced in large amounts by tissues Produced in large amounts by tissues

undergoing senescence or ripeningundergoing senescence or ripening Occurs in all plant organsOccurs in all plant organs

ETHYLENE

Stimulate elongation of stems, petioles, roots Stimulate elongation of stems, petioles, roots and floral structure of aquatic and semiaquatic and floral structure of aquatic and semiaquatic plantsplants

Ethylene promotes gibberellin synthesis in rice Ethylene promotes gibberellin synthesis in rice to promote root and shoot elongationto promote root and shoot elongation

While in peas, root and shoot elongation While in peas, root and shoot elongation inhibited by ethyleneinhibited by ethylene

Stimulate abnormal growth response such as Stimulate abnormal growth response such as swelling of stem tissues and downward swelling of stem tissues and downward curvature of leaves (epinasty)curvature of leaves (epinasty)

Vegetative developmentVegetative development

Physiological effects of ethylene

Stimulate fruit ripening: banana, apple avocado Stimulate fruit ripening: banana, apple avocado etc..etc..

Ethylene is autocatalyticEthylene is autocatalytic release of ethylene gas by ripening fruitsrelease of ethylene gas by ripening fruits will in turn stimulate premature climactericwill in turn stimulate premature climacteric and ethylene production by other fruits stored and ethylene production by other fruits stored

nearnear Number of qualitative metabolic changes are Number of qualitative metabolic changes are

initiated in fruit initiated in fruit

Fruit RipeningFruit Ripening

Changes in fruit ripening:Changes in fruit ripening:

During ripening promote production of sugars, During ripening promote production of sugars, which increase sweetness (breakdown of starch which increase sweetness (breakdown of starch and acid) and odor and acid) and odor

Induced rupture of cell membranes and water loss Induced rupture of cell membranes and water loss from tissues: increase cell wall softening by the from tissues: increase cell wall softening by the action of enzymesaction of enzymes

Involved breakdown of chlorophyll and synthesis Involved breakdown of chlorophyll and synthesis of pigments of pigments

Synthesis of flavorSynthesis of flavor

Ethylene has important Ethylene has important commercial usescommercial uses

Storage facilities developed to inhibit ethylene Storage facilities developed to inhibit ethylene production and promote preservation of fruits production and promote preservation of fruits have a controlled atmosphere of have a controlled atmosphere of low Olow O22

concentrationconcentration and and low temperaturelow temperature that inhibits that inhibits biosynthesisbiosynthesis

High concentration of COHigh concentration of CO22 (3-5%) prevents (3-5%) prevents

ethylene actionethylene action

Low pressure to remove ethylene and oxygen Low pressure to remove ethylene and oxygen from storage chamberfrom storage chamber

Use of inhibitors of ethylene actionUse of inhibitors of ethylene action

Such as COSuch as CO22 and Ag and Ag++ (silver) (silver)

Will delay or prevent ripeningWill delay or prevent ripening

Ethylene has high diffusion rateEthylene has high diffusion rate

Difficult to apply in a gas formDifficult to apply in a gas form

Spray ethylene releasing compound such as Spray ethylene releasing compound such as ethepon ethepon

When taken up by plant tissue, ethepon is When taken up by plant tissue, ethepon is converted to ethyleneconverted to ethylene

BrassinosteroidsBrassinosteroids

Steroid hormonesSteroid hormones Chemical structure similar to animal steroid Chemical structure similar to animal steroid

hormoneshormones Brassinolides most biologically actveBrassinolides most biologically actve Functions: brassinosteroids promote stem Functions: brassinosteroids promote stem

elongation in mutant plants, shoot elongation elongation in mutant plants, shoot elongation and ethylene productionand ethylene production

Inhibits root growth and developmentInhibits root growth and development