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5 Major Plant Hormones, Precursors and their Function|| A Simplified Summary|| Biologyexams4u | biologyexams4u | YouTubeToText
YouTube Transcript: 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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