plant responses to hormones
Post on 07-Jan-2016
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Plant responses to Plant responses to hormoneshormones
What the spec says….What the spec says….
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
Growth substances can be…Growth substances can be…
Synergistic – enhance each others’ Synergistic – enhance each others’ effectseffects
Antagonistic – counteract each otherAntagonistic – counteract each other
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
Phototropism experimentsPhototropism experiments
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)
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
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
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
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.
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
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
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
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
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
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