Lecture 4

Question 1

What are phytohormones

Answer 1

regulate all stages of the plant life cycle and its defense and stress response

Question 2

What are the 5 common phytohormones

Answer 2

auxin
cytokinin
gibberellin
abscisic acid
ethylene

Question 3

what are the newly discovered phytohormones

Answer 3

Brassinosteroid
salicylic acid
strigolactone
jasmonic acid

Question 4

What is the effect of salicylic acid

Answer 4

painkiller

plant hormone

Question 5

What is the effect of strigolactone

Answer 5

blocks axillary shoots

Question 6

When was cytokinin discovered

Answer 6

1941

Question 7

How was cytokinin discovered

Answer 7

demonstrated in plant culture the growth promoting properties of coconut milk

Question 8

When did Letham and Miller purify zeatin (natural cytokinin) from Zea Mays

Answer 8

1973

Question 9

Why is this hormone given the name cytokinin

Answer 9

for their growth promoting properties

cytokinesis = cell division

Question 10

Where are cytokinins synthesized from

Answer 10

adenine

Question 11

What are the natural cytokinins

Answer 11

zeatin

IPA

Question 12

What are the synthetic cytokinins

Answer 12

Kinetin

BAP

Question 13

What are the properties of cytokinins

Answer 13

• promotes growth and cell division
• delay tissue senescence
• act antagonistically to auxin :
  promotes shoot vs root development in cultured cells.
  blocks adventitious rooting

Question 14

true or false; cytokinins affect grain production and drought tolerance

Answer 14

true

Question 15

What happens to rice plants that accumulate more CK

Answer 15

can produce more grain per plant because of changes in inflorescence growth

Question 16

What happens to tobacco plants that produce more CK

Answer 16

they are more drought tolerant because of the delay of leaf senescence conferred by CK

Question 17

What are commercial uses of CK

Answer 17

antioxidants in cut salads

release of axillary buds

Question 18

How was ethylene discovered

Answer 18

• noticed because of effect of gas street lights in the 1800s on adjacent plants
• it is the first plant hormone identified
• leaking gas caused early leaf drop

Question 19

true or false; ethylene is a gas

Answer 19

true

Question 20

when was ethylene discovered as an active ingredient

Answer 20

1901

Question 21

Where is ethylene derived from

Answer 21

methionine

Question 22

What are the effects of ethylene

Answer 22

a ripening hormone

Question 23

What fruits make ethylene

Answer 23

tomatoes, apples, bananas, avocado

• make ethylene
• ripen in response to exogenous (added) ethylene

Question 24

Why does bad apple spoil the whole bunch

Answer 24

this is because a ripening apple (or infected) gives off ethylene, which induces ripening in the surrounding apples

Question 25

What does ethylene promote

Answer 25

- fruit ripening (promotes food softening and color development) - senescence - abscission of leaf, petals, fruit

Question 26

What does senescence mean

Answer 26

controlled process of growing old and redistribution of nutrients to growing parts of the plant

Question 27

true or false; in some cases senescence is terminated by abscission of the senescencing region

Answer 27

true

Question 28

what are snorkel genes in rice

Answer 28

- ethylene induced elongation, so rice submerged or floating in water can produce a snorkel to keep pace with rising flood waters ( anaerobic conditions)

Question 29

How are ethylene mutants detected

Answer 29

on an agar plate all Arabidopsis seedlings are sprayed with ethylene gas. The non mutants have their growth inhibited whilst the mutant will grow tall

Question 30

Where is ethylene normally produced

Answer 30

shoot tip - to enable seedlings to avoid obstacles when it is germinating and growing - produced in response to wounding

Question 31

true or false; ethylene induces a triple response in seedlings

Answer 31

true

Question 32

What does it mean by triple response

Answer 32

as increasing amounts of ethylene are sprayed on the seedlings; they will curve, grow thicker and become shorter and shorter - used arabidopsis mutants to work out ethylene signalling pathway

Question 33

What are the commercial uses of ethylene (adding)

Answer 33

- ripening stimulation (tomatoes, bananas) | - induction of abscission prior to mechanical harvest (cherries)

Question 34

commercial uses of ethylene (blocking or removing it)

Answer 34

- removal of ethylene gas (scrubbing) during apple storage (to halt ripening and spoilage) - treatment of cut flowers with silver ions (block ethylene perception) to stay fresh longer

Question 35

Who discovered Gibberellin and when

Answer 35

Kurosawa 1926 "foolish seedling disease"

Question 36

How was Gibberellin discovered

Answer 36

compound secreted by fungus Gibberella fujikuroi - in rice caused excessive shoot elongation, grain poor or absent - named Gibberellin after the fungus

Question 37

true or false; there are 80 natural GA molecules made from mevalonate pathway

Answer 37

true

Question 38

What is the classic role of Gibberellin (GA)

Answer 38

Hyper elongation of shoots by stimulation of both cell division and cell elongation (tall plants) - seed germination - stimulation of flowering in long day and biennial plants - fruit development

Question 39

What initiated the Green Revolution of the 20th century - genes controlling GA synthesis - due to GA mutants

Answer 39

due to increased use of fertilizer and introduction of semi dwarf varieties of gran - semi dwarf varieties put more energy into seed production than stem growth and are sturdier and less likely to fall over

Question 40

What are commercial uses of GA

Answer 40

- parthenocarpic development of fruit gives seedless table grapes

Question 41

What does parthenocarpy mean

Answer 41

fruit development in the absence of seeds

Question 42

What are the properties of ABA (abscisic acid)

Answer 42

found in: - dormant seeds (dried out) - buds and water stressed tissues such as mature leaves effects: not involved in abscission

Question 43

Where is ABA made from

Answer 43

mevalonate pathway

Question 44

What are the major roles of ABA

Answer 44

protect the plant from water stress | induces stomatal closure (reduces transpiration and water loss)

Question 45

what is the 'ein' mutant

Answer 45

an ethylene insensitive mutant | - fails to undergo triple response in the presence of ethylene

Question 46

What is the 'ctr' mutant

Answer 46

a constitutive triple response mutant | - undergoes the triple response even in the absence of ethylene

Question 47

What is the effect of GA3 on the growth of Thomson seedless grapes

Answer 47

looser cluster of larger grapes

Question 48

What are Brassinosteroids

Answer 48

are steroid molecules similar to cholesterol | and to animal hormones; purified from rapeseed

Question 49

What is brassinosteroid required for

Answer 49

- required for normal plant development | - stimulate cell division and elongation