Ethylene: gas hormone

• Overview• Chemistry• Conditions of

production• Physiological effects• Mode of action

History

• Gas hormone (C2H4) • Citrus growers and kerosene heaters/ fruit

ripening • bioassay for the triple response

Biosynthesis

• synthesized from Methionine

• ACC • ACC oxidase

produces ethylene • requires oxygen • not conjugated • catabolized to

ethylene oxide or CO2

Conditions of production• flooding • transport of ACC • no O2 in roots for

ethylene production• senescence • wounding • drought stress • IAA--some effects of

auxin are actually ethylene

Physiological effects Triple response

• Effective @ 1ul/L • Abscission • Fruit Ripening • Developmental

effects

Inhibition of flower senescence

Abscission

• reduces auxintransport

• seperation layer

Abscission

Wild type ethylene insensitive

Fruit Ripening

• climacteric fruits: examples

• respiratory burst • ACC first then

ethylene • targets cell wall

softening • cellulase in avocado

Climacteric fruits

ethephon: synthethic ethylene

• synchronize ripening • conditions slow ripening: high CO2/cool

temperatures/low O2

Root hair formation

Air ethylene

Epinasty

Mode of action

• ethylene receptor • membrane protein• Inactivated• Allows ethylene

response pathway • activates transcription

Activation of genes