Plant Hormones and Growth Regulators Part 2 Ethylene & ABA Flashcards
In Ancient times, people in China used to
burn incense in rooms to cause fruits to ripen
more quickly.
In 1800’s gas leaks associated with street
lamps
caused leaves to fall off trees
Ethylene
C2H4 (gaseous hormone)
First shown to be made by plants in 1934
Ethylene in general
- Some negative and some positive effects
- Wound hormone
– Ethylene concentrations increase after wounding - Ethylene promotes it own synthesis (autocatalytic)
- High auxin concentrations promote ethylene
synthesis
– Explains why high auxin concentrations are inhibitory
Roles of Ethylene 1
Causes leaf abscission.
Causes leaf abscission.
Causes an increase in cellulase activity in
abscission zone.
Roles of Ethylene 2
2) Promotes flowering in some species e.g. pineapples
2) Promotes flowering in some species e.g. pineapples
- In Hawaii treat pineapples with NAA (synthetic auxin) to
promote ethylene synthesis. - Bonfires are started to cause flowering of pineapples
Roles of Ethylene 3
3) Promotes ripening of climacteric fruits
*One part per million will cause ripening
People used to gash fruits in Egypt why
– The wounding resulted in ethylene synthesis that
promoted ripening
Ethylene used commercially to
to ripen bananas,
honeydew melons, color up citrus fruits
ethylene Only climacteric fruits respond
– They have a major increase in respiration prior to
ripening, and ethylene levels increase by 100X
– Will continue to ripen after they are picked
Roles continued ethylene 4
promoting fruit spoiling
Post harvest physiology:
- Almost no ethylene in the absence of oxygen
- Carbon dioxide and silver are inhibitors of ethylene
- Fruits are shipped in trucks with carbon dioxide
- Fruits are stored at low temperatures in nitrogen or
carbon dioxide
ethylesnes roles 5
5) Promotes leaf and flower senescence.
Senescence
breakdown of cellular components
leading to death
Florists keep flowers
cool, and some use carbon
dioxide as an inhibitor
– Other hormones exert anti-senescence effect:
* Auxin in low concentrations
* Gibberellins
* Cytokinins
Roles ethynol
6) Affects growth and ultimate form of plants.
Epinasty
increased growth on upper surface that causes
downward bending
* 2,4 D and other auxin –based herbicides cause this
ethylene causes roots and stem
thickenig
(thigmomorphogenesis
Wind causes shorter and thicker plants by inducing ethylene synthesis
thigmomorphogenesis
changes in morphology in response to touch
ethylene Affects seedlings as they grow through the soil
Pressure of the soil causes seedlings to curve and have a hook
due to ethylene synthesis
Abscisic Acid (ABA)
dormin
misnomers
made in plastids
misnomers
Not involved in leaf abscission (except
perhaps in cotton
