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5 Major Plant Hormones, Precursors and their Function|| A Simplified Summary|| Biologyexams4u

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do you know the agent orange the toxic

herbicide widely used by the us military

during u.s vietnam war

is a synthetic plant hormone

this agent orange is sprayed using

helicopters in vietnam forest

to uncover the soldiers and also to

cause crop loss

and this is the image that shows the

defoliation or shedding of leaves caused

by this chemical

the drastic effect of this disastrous

chemical still persists

as long-term illness birth defects

cancers etc agent orange is made up of

two synthetic auxins or synthetic plant hormones

hormones

two for dichlorophenoxy acetic acid and

two for trichlorophenoxy acetic acid

hi friends welcome to biology

exams4u.com today's topic of our

discussion is how plant hormones

regulate plant growth and development

within 5-10 minutes

at the end of the discussion you will be

having a simplified clear-cut

understanding about plant hormones and

precursors how they are classified as

growth promoters and growth inhibitors

role of major plant hormones

auxin chipper and cytokine in ethylene

and aba within 5-10 minutes

if you are new to this channel please

consider subscribing this channel

plant hormones just like animal hormones

are chemicals that is produced in minor

quantities by plants that regulates

growth and development of plants

it's broadly classified into growth

promoters and growth inhibitors growth

promoters means plant hormones that is

involved in cell division and cell differentiation

differentiation

and that includes auxin

giberline and cytokinin

whereas growth inhibitors

the term indicates that is not involved

in cell division these are also

essential hormones that is involved in

abscission or senescence or natural

detachment of ripened leaves and fruits

from the plant thus helping to complete

the life cycle that includes abscisic

acid and ethylene abscisic acid is also

called as stress hormone

whereas ethylene is called as ripening hormone

hormone

also called the senescence hormone

now let us see the precursors of these hormones

hormones auxin

auxin

the precursor is amino acid tryptophan

whereas giberline it's formed

through maybelonic pathway are still

coenzyme a is a precursor but the

immediate precursor is carbonic acid

whereas cytokinin as you see it is an

adenine derivative the precursor is

adenosine monophosphate

whereas abscisic acid the precursor is zeaxanthin

zeaxanthin

and finally ethylene

the glaciers hormone the precursor is

amino acid methionine exactly it is s

adenosine methionine that is converted

to acc or amino cyclopropyl

carboxylic acid therefore the immediate

precursor of ethylene is acc chasmonic

acid brassinolite salicylic acid etc are

primarily involved in plant defense

let's move into the detail of each of

this plant hormone starting with auxin

auxin are growth promoters that is

involved in growth cell division and

cell differentiation

in tissue culture

high oxygen concentration to cytokine ratio

ratio

furthers root formation

whereas low oxygen to cytokinin ratio

fevers shoot formation

intermediate concentration fervors

callus and this

combination is applicable to maturity of

plants so oxycytokinin together are

widely used in tissue culture for

shooting and rooting and also for callus

formation auxin favors

epical butt dominance or activation of

apical but whereas it inhibits lateral bud

bud

activation or keeps lateral butt dormant

auxin promotes epical bar dominance it

follows germination that means it breaks

the dormancy

it is involved in flowering of many

plants or promotes flowering in many

plants auxin promotes fruiting

especially parthenocarpi the formation

of fruits without fertilization thereby

forming seedless fruits

it prevents abscission or falling off

leaves or aging senescence as it is a

growth promoter it inhibits aging or senescence

senescence

it breaks dormancy as it furthers germination

germination

these are the major roles of auxin

regarding the transport of oxygen oxygen

is often synthesized

at shoot tip or shoot meristem

meristematic region

transport is top to bottom and is polar

and top to bottom transport is called as

there are different types of auxins

natural locks oxygen the most common one

is indole acetic acid then there is iba

phenylalactic acid etc

synthetic auxins include 240

245 t

then naa

methoxy dichlorobenzoic acid these are

widely used as we decides this 240

dicamba and piccoloram these are widely

used as we decides

that selectively eliminates broadleaved

plants or thai cut plants na is widely

used as rooting hormone

widely used as rooting hormone

as we mentioned earlier agent orange is

a combination of 240 and

second one is keeperlin chipperlin

chipperlin

is also a growth promoter it is

primarily involved in cell division

thereby causing stem elongation

this is a roasted plant or a dwarf plant

this dwarfism can be reversed by

treating with giberlin so when treated

with giberline as you can see there is

internal elongation this is

international elongation

by the application of jperlin

and also flowering this

rapid growth or rapid illumination and

flowering is often termed as bolting

so reversal of darfism or stem

elongation is possible by the

application of giberline or

then it promotes germination

it is involved in flowering promotes

flowering of many plants

it promotes fruiting just like oxygen

it prevents abscession as is a growth

promoter it prevents abscession or aging

aging

it breaks dormancy as it promotes germination

germination

regarding the transport

kuberlin transport there is no polarity

it moves upwards and downwards

so the transport is non-polar unlike auxin

auxin

where transport is polar

so these are the different types of

hyperlinks nearly 136 different

gibberellins molecules have been

identified ga3 is the most studied and

the most common

whereas ga1 is involved in elongation

whereas gn iron is involved in flowering

like that

next one is cytokinin cytokine is a

growth promoter therefore it further

cell division and differentiation

we have mentioned this already high

cytokinin ratio to auxin fervor's shoot formation

formation

in tissue culture whereas

whereas

low cytokine into high oxygen ratio fervors

fervors

root formation in tissue culture

cytokinin is a hormone that is

antagonistic to auxin's activity

activity

auxin favors epical blood dominance

whereas cytokinin fevers

lateral blood growth it follows lateral

bud growth thereby inhibiting a pickle

bud dominance

it furthers germination it favors

flowering in many plants

promotes fruiting in many plants

often causes opening of stomata

it inhibits abscission

or aging

or senescence

it breaks dormancy and as it favors germination

germination

regarding the transport toxin is often synthesized

synthesized

in roots so the transport is from bottom

to top

and often it is called as acropetal

acropatal transport

it is an adenine derivative kinetic is a

synthetic cytokinin whereas xetin is a

natural cytokinin that is from

z mace

now ethylene ethylene is also called as

ripening hormone or senescence hormone

inhibits growth or cell division

it furthers germination

promotes flowering in some plants

fruiting in some plants

it fervors abscission it is involved in

abscission or natural detachment of

ripened leaves and fruits

from the plant

this is the activity of ethylene it

cause falling or natural detachment of

ripened leaves and fruits

what is actually happening is the oxygen

concentration is decreased then the

ethylene concentration is increased at

the site of detachment then

allowing of leaves occurs

there will be chlorophyll degradation

then formation of an absorption layer

let me zoom in this region as you can

see this is the absorption layer this

absorption layer is made up of thin

layer of cells so

causes the detachment

without causing wound

so ethylene causes the abscission

without causing any wound so it's an

important process

for dispersal of

seeds and also

providing nutrients to young leaves and

young parts of the plant

then it

breaks dormancy as it favors germination

then one more point to add is when

seedlings are treated with ethylene

there is a typical response a triple

response seedling stem stops elongation

elongation is stopped

then the stem thickens there is a

horizontal thickness of stem followed by

bending of seedlings forming a hook leg structure

structure

so this is called triple response

when seedlings are treated with ethylene

there is a typical response which is

called as triple response

regarding the transport of ethylene

ethylene is a cases hormone therefore it diffuses

diffuses

it moves by diffusion

to all parts of the plant

and finally abscisic acid abscisic acid

is also called as stress hormone it

inhibits growth

it is primarily produced during drought

condition or flooding when there is a

stress abscisic acid is synthesized more

that's why it is called a stress hormone

it prevents germination

promotes flowering in shorter plants

promotes fruiting in some plants

causes tomato closure especially during

flooding and drought

so that the transpiration rate is

minimized water loss is minimized

it favors abscission just like ethylene

both work together in abscission and ripening

ripening

abscisic acid is involved in

maintaining or promoting dormancy

during drought and flooding this

absolute catastrophic concentration increases

increases

in root especially in root

then it closes the stomach stomatal

closure thereby prevent water loss

so abscisic acid is primarily involved

in plants survival mechanism during

flooding and throat that's why it's

called as a stress hormone

regarding the transport there is no polarity

polarity

it can move up and down abscisic acid is

can move up and down of the plant

without any specific polarity

abscisic acid and ethylene actually controls

controls

abscission or natural detachment of

ripened leaves and fruits from the plant

and that is about the plant hormones

thank you so much for your support

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5 Major Plant Hormones, Precursors and their Function|| A Simplified Summary|| Biologyexams4u