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Plant responses Plant responses to hormones to hormones

Plant responses to hormones

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Plant responses to hormones. What the spec says…. Types of plants hormone. Cell division. Cell elongation. Auxins Gibberellins Cytokinins Abscisic acid Ethene. Promotors of growth. Initiation of organs. Differentiation. Inhibitors of growth / Antagonists to growth stimulators. - PowerPoint PPT Presentation

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Page 1: Plant responses to hormones

Plant responses to Plant responses to hormoneshormones

Page 2: Plant responses to hormones

What the spec says….What the spec says….

Page 3: Plant responses to hormones

Types of plants hormoneTypes of plants hormone

1.1. AuxinsAuxins

2.2. GibberellinsGibberellins

3.3. CytokininsCytokinins

4.4. Abscisic acidAbscisic acid

5.5. EtheneEthene

Promotors of growth

Inhibitors of growth /Antagonists to growth stimulators

Cell division Cell elongation

Differentiation Initiation of organs

Page 4: Plant responses to hormones

Growth substances can be…Growth substances can be…

Synergistic – enhance each others’ Synergistic – enhance each others’ effectseffects

Antagonistic – counteract each otherAntagonistic – counteract each other

Page 5: Plant responses to hormones

AuxinAuxin

Indoleacetic acidIndoleacetic acid Causes elongation of cellsCauses elongation of cells

– Increases plasticity of cellsIncreases plasticity of cells– Cell walls softenCell walls soften– Cell becomes less turgid and take up Cell becomes less turgid and take up

more watermore water– Cell expandsCell expands

Responsible for phototropismResponsible for phototropism

Page 6: Plant responses to hormones

Phototropism experimentsPhototropism experiments

Page 7: Plant responses to hormones

Other activities of auxinsOther activities of auxins

Apical dominance – apical bud Apical dominance – apical bud inhibits lateral (axillary buds)inhibits lateral (axillary buds)– E.g. pruning stimulates axillary budsE.g. pruning stimulates axillary buds

Formation of lateral roots – Formation of lateral roots – stimulates INITIATION of lateral roots stimulates INITIATION of lateral roots and adventitious rootsand adventitious roots– E.g. napthalene acetic acid (NAA)E.g. napthalene acetic acid (NAA)– Indole butyric acid (IBA)Indole butyric acid (IBA)

Page 8: Plant responses to hormones

More auxin functionsMore auxin functions

Abscission of leaves and fruitAbscission of leaves and fruit Abscission = falling of fruit and Abscission = falling of fruit and

leavesleaves IAA – delays early stages, promotes IAA – delays early stages, promotes

later stages later stages – Stimulates ethene productionStimulates ethene production– Ensure fruit stays on trees until harvestEnsure fruit stays on trees until harvest

Page 9: Plant responses to hormones

Even more auxin functionsEven more auxin functions

Fruit developmentFruit development– Produced in pollen & developing seedProduced in pollen & developing seed– Stimulates fruit development after Stimulates fruit development after

fertilisationfertilisationUsed in production of seedless fruitsUsed in production of seedless fruits

Weed killersWeed killers– 2,4-D causes abnormal growth of Dicots 2,4-D causes abnormal growth of Dicots

(e.g. dandelions) monocots are (e.g. dandelions) monocots are unaffectedunaffected

Page 10: Plant responses to hormones

GiberellinsGiberellins

Stem elongation in dwarf plantsStem elongation in dwarf plants– E.g. dwarf peasE.g. dwarf peas

Bolting of long day plants when the Bolting of long day plants when the days are short i.e. cause them to days are short i.e. cause them to flowerflower

Overcome lack of cold period Overcome lack of cold period required for flowering in long day required for flowering in long day plantsplants

Page 11: Plant responses to hormones

A wild type rice plant A wild type rice plant (left) compared to a (left) compared to a semidwarf transgenic semidwarf transgenic plant (right) plant (right) containing  the containing  the gaigai mutant allele. mutant allele. 

The The gaigai mutant allele mutant allele confers giberellin confers giberellin insensitivity upon the insensitivity upon the transgenic plant, and transgenic plant, and causes its reduced causes its reduced stature.stature.

Page 12: Plant responses to hormones

More giberellinsMore giberellins

Fruit developmentFruit development– Stimulates growth of fruit stalkStimulates growth of fruit stalk– Delays senescence (aging)Delays senescence (aging)

Seed germination – stimulatesSeed germination – stimulates Stimulate Stimulate αα – amylase production in – amylase production in

seeds, improves malt yields from seeds, improves malt yields from barleybarley

Page 13: Plant responses to hormones

CytokininsCytokinins

Produced by meristemic tissueProduced by meristemic tissue– Apices of roots and shootsApices of roots and shoots

Development of roots, shoots and lateral Development of roots, shoots and lateral budsbuds

Cell enlargementCell enlargement Maturation of chloroplastsMaturation of chloroplasts

Dependant on auxin for functionDependant on auxin for function

Page 14: Plant responses to hormones

Cytokinins are Cytokinins are commonly used tocommonly used tostimulate shoot stimulate shoot initiation in culture initiation in culture as is shown by as is shown by shoot/bulblet shoot/bulblet formation on bulb formation on bulb scales of scales of BowieaBowieavolubilis. volubilis. Benzyladenine was Benzyladenine was used here to stimulate used here to stimulate shoot growth shoot growth

Page 15: Plant responses to hormones

Abscissic acidAbscissic acid

Inhibit / alter growthInhibit / alter growth Linked to environmental stressLinked to environmental stress

– Seeds can become dormantSeeds can become dormant– Abscission of leaves, flowers and fruitsAbscission of leaves, flowers and fruits– Close stomata in times of water Close stomata in times of water

deficiencydeficiency

Page 16: Plant responses to hormones
Page 17: Plant responses to hormones

Ethene (ethylene)Ethene (ethylene)

Promotes ripening of fruitsPromotes ripening of fruits Promotes abscission (auxin prevents Promotes abscission (auxin prevents

it)it)– Abscission layerAbscission layer

Antagonistic to auxinAntagonistic to auxin