Samenvatting Plant physiology H7: Ethylene
Introduction:
• GAS so special
• Has a triple response = 3 different responses
o Short hypocotyl & root
o Exaggerated apical hook
o Swelling of the hypocotyl
• Plants produce this gas, some pathogens produce it as well
• Major hazard → flammable, advantage → you need a lot of it to be dangerous
Ethylene Biosynthesis:
• Production requires oxygen
• Produced from methionine with 1-aminocyclopropane-1-carboxylic acid (ACC) as
precursor
o Part of the Yang cycle that recycles MTA towards methionine
o Synthesis of S-adenosyl-L-methionine (SAM) through SAM synthetase
o ACC-synthase (cytosolic enzyme) catalyzes SAM → ACC + MTA
o ACC-oxidase (cytosolic & nuclear) catalyzes ACC → ethylene
▪ Requires oxygen, Fe2+, bicarbonate/CO2, Ascorbic acid (Vit C)
o NOTE: HCN is a side product → this is deadly but it is luckily detoxified into -
cyanoalanine by -cyanoalanine synthase
• Both synthase & oxidase have inhibitors
• ACC-oxidase has 3(4) derivatives
o 1-malonyl-ACC (MACC)
▪ By AMT
▪ Only activated by ethylene treatment in unripe stages
▪ MACC hydrolase (unknown) can reconverse MACC to ACC
o Jasmonic acid ACC (JA-ACC)
▪ By JAR1 = jasmonic acid amino synthetase
o -glutamyl-ACC (GACC)
▪ By GGT = gamma-glutamyltranspeptidase
o -ketobutyrate
▪ By ACC-deaminase from plant growth promoting bacteria (PGPB)
,Ethylene Transport:
• Gas so this is transported through diffusion & can’t really be regulated → regulation
happens in the ACC transport
• ACC transport
o LHT1 = Lysine histidine transporter 1 (high affinity)
o Long distance
o Xylem mediated
▪ Both epinasty & hyponasty can happen (species specific)
▪ By flooding, ethylene production is only & even more done by the
shoots
o Phloem mediated
, Ethylene Signaling:
• ETR1 is the main ethylene receptor
• Again, like the 2-component system
• A functional receptor is a dimer, otherwise they are not functional
• The ethylene receptor has 3 states → on – intermediate – off
• They are bound at the ER membrane bcs ethylene is hydrophobic, so it likes to be in
the hydrophobic environment of the membrane
• It is a negative regulator of ethylene signaling, so:
o No ethylene → receptor = ON → no ethylene responses
o Ethylene → receptor = OFF → ethylene responses
• Cu is a cofactor & essential for ethylene binding, Ag is a competitive antagonist
(reverts the reaction)
• The receptor interacts with CTR1 = constitutive triple response 1 (kinase)
o This is a negative regulator of ethylene sigaling
▪ Active CTR1 represses ethylene signal
▪ Inactive CTR1 allows ethylene responses
o This means that you have a double negative signaling
Introduction:
• GAS so special
• Has a triple response = 3 different responses
o Short hypocotyl & root
o Exaggerated apical hook
o Swelling of the hypocotyl
• Plants produce this gas, some pathogens produce it as well
• Major hazard → flammable, advantage → you need a lot of it to be dangerous
Ethylene Biosynthesis:
• Production requires oxygen
• Produced from methionine with 1-aminocyclopropane-1-carboxylic acid (ACC) as
precursor
o Part of the Yang cycle that recycles MTA towards methionine
o Synthesis of S-adenosyl-L-methionine (SAM) through SAM synthetase
o ACC-synthase (cytosolic enzyme) catalyzes SAM → ACC + MTA
o ACC-oxidase (cytosolic & nuclear) catalyzes ACC → ethylene
▪ Requires oxygen, Fe2+, bicarbonate/CO2, Ascorbic acid (Vit C)
o NOTE: HCN is a side product → this is deadly but it is luckily detoxified into -
cyanoalanine by -cyanoalanine synthase
• Both synthase & oxidase have inhibitors
• ACC-oxidase has 3(4) derivatives
o 1-malonyl-ACC (MACC)
▪ By AMT
▪ Only activated by ethylene treatment in unripe stages
▪ MACC hydrolase (unknown) can reconverse MACC to ACC
o Jasmonic acid ACC (JA-ACC)
▪ By JAR1 = jasmonic acid amino synthetase
o -glutamyl-ACC (GACC)
▪ By GGT = gamma-glutamyltranspeptidase
o -ketobutyrate
▪ By ACC-deaminase from plant growth promoting bacteria (PGPB)
,Ethylene Transport:
• Gas so this is transported through diffusion & can’t really be regulated → regulation
happens in the ACC transport
• ACC transport
o LHT1 = Lysine histidine transporter 1 (high affinity)
o Long distance
o Xylem mediated
▪ Both epinasty & hyponasty can happen (species specific)
▪ By flooding, ethylene production is only & even more done by the
shoots
o Phloem mediated
, Ethylene Signaling:
• ETR1 is the main ethylene receptor
• Again, like the 2-component system
• A functional receptor is a dimer, otherwise they are not functional
• The ethylene receptor has 3 states → on – intermediate – off
• They are bound at the ER membrane bcs ethylene is hydrophobic, so it likes to be in
the hydrophobic environment of the membrane
• It is a negative regulator of ethylene signaling, so:
o No ethylene → receptor = ON → no ethylene responses
o Ethylene → receptor = OFF → ethylene responses
• Cu is a cofactor & essential for ethylene binding, Ag is a competitive antagonist
(reverts the reaction)
• The receptor interacts with CTR1 = constitutive triple response 1 (kinase)
o This is a negative regulator of ethylene sigaling
▪ Active CTR1 represses ethylene signal
▪ Inactive CTR1 allows ethylene responses
o This means that you have a double negative signaling
