Plant Hormones and Growth Regulators Part 2 Ethylene & ABA

Question 1

In Ancient times, people in China used to

Answer 1

burn incense in rooms to cause fruits to ripen
more quickly.

Question 2

In 1800’s gas leaks associated with street
lamps

Answer 2

caused leaves to fall off trees

Question 3

Ethylene

Answer 3

C2H4 (gaseous hormone)
First shown to be made by plants in 1934

Question 4

Ethylene in general

Answer 4

• 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

Question 5

Roles of Ethylene 1

Answer 5

Causes leaf abscission.

Question 6

Causes leaf abscission.

Answer 6

Causes an increase in cellulase activity in
abscission zone.

Question 7

Roles of Ethylene 2

Answer 7

2) Promotes flowering in some species e.g. pineapples

Question 8

2) Promotes flowering in some species e.g. pineapples

Answer 8

• In Hawaii treat pineapples with NAA (synthetic auxin) to
  promote ethylene synthesis.
• Bonfires are started to cause flowering of pineapples

Question 9

Roles of Ethylene 3

Answer 9

3) Promotes ripening of climacteric fruits
*One part per million will cause ripening

Question 10

People used to gash fruits in Egypt why

Answer 10

– The wounding resulted in ethylene synthesis that
promoted ripening

Question 11

Ethylene used commercially to

Answer 11

to ripen bananas,
honeydew melons, color up citrus fruits

Question 12

ethylene Only climacteric fruits respond

Answer 12

– They have a major increase in respiration prior to
ripening, and ethylene levels increase by 100X
– Will continue to ripen after they are picked

Question 13

Roles continued ethylene 4

Answer 13

promoting fruit spoiling

Question 14

Post harvest physiology:

Answer 14

• 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

Question 15

ethylesnes roles 5

Answer 15

5) Promotes leaf and flower senescence.

Question 16

Senescence

Answer 16

breakdown of cellular components
leading to death

Question 17

Florists keep flowers

Answer 17

cool, and some use carbon
dioxide as an inhibitor
– Other hormones exert anti-senescence effect:
* Auxin in low concentrations
* Gibberellins
* Cytokinins

Question 18

Roles ethynol

Answer 18

6) Affects growth and ultimate form of plants.

Question 19

Epinasty

Answer 19

increased growth on upper surface that causes
downward bending
* 2,4 D and other auxin –based herbicides cause this

Question 20

ethylene causes roots and stem

Answer 20

thickenig
(thigmomorphogenesis
Wind causes shorter and thicker plants by inducing ethylene synthesis

Question 21

thigmomorphogenesis

Answer 21

changes in morphology in response to touch

Question 22

ethylene Affects seedlings as they grow through the soil

Answer 22

Pressure of the soil causes seedlings to curve and have a hook
due to ethylene synthesis

Question 23

Abscisic Acid (ABA)

Answer 23

dormin
misnomers
made in plastids

Question 24

misnomers

Answer 24

Not involved in leaf abscission (except
perhaps in cotton

Question 25

ABA roles

Answer 25

– Makes buds become dormant and stay dormant
– Keeps seeds dormant
– Causes stomates to close

Question 26

Makes buds become dormant and stay dormant

Answer 26

Promotes formation of bud scales

Question 27

Keeps seeds dormant

Answer 27

GAs break dormancy

Question 28

Causes stomates to close

Answer 28

ABA levels rise and cause stomates to close