Lecture 4 Flashcards
Hormone function to co-ordinate plant development as well as responses to the environment. Genetic studies, mainly in Arabidopsis, have led to a greatly improved knowledge of genes involved in hormone perception and response
What are phytohormones
regulate all stages of the plant life cycle and its defense and stress response
What are the 5 common phytohormones
auxin cytokinin gibberellin abscisic acid ethylene
what are the newly discovered phytohormones
Brassinosteroid
salicylic acid
strigolactone
jasmonic acid
What is the effect of salicylic acid
painkiller
plant hormone
What is the effect of strigolactone
blocks axillary shoots
When was cytokinin discovered
1941
How was cytokinin discovered
demonstrated in plant culture the growth promoting properties of coconut milk
When did Letham and Miller purify zeatin (natural cytokinin) from Zea Mays
1973
Why is this hormone given the name cytokinin
for their growth promoting properties
cytokinesis = cell division
Where are cytokinins synthesized from
adenine
What are the natural cytokinins
zeatin
IPA
What are the synthetic cytokinins
Kinetin
BAP
What are the properties of cytokinins
- promotes growth and cell division
- delay tissue senescence
- act antagonistically to auxin :
promotes shoot vs root development in cultured cells.
blocks adventitious rooting
true or false; cytokinins affect grain production and drought tolerance
true
What happens to rice plants that accumulate more CK
can produce more grain per plant because of changes in inflorescence growth
What happens to tobacco plants that produce more CK
they are more drought tolerant because of the delay of leaf senescence conferred by CK
What are commercial uses of CK
antioxidants in cut salads
release of axillary buds
How was ethylene discovered
- 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
true or false; ethylene is a gas
true
when was ethylene discovered as an active ingredient
1901
Where is ethylene derived from
methionine
What are the effects of ethylene
a ripening hormone
What fruits make ethylene
tomatoes, apples, bananas, avocado
- make ethylene
- ripen in response to exogenous (added) ethylene
Why does bad apple spoil the whole bunch
this is because a ripening apple (or infected) gives off ethylene, which induces ripening in the surrounding apples
What does ethylene promote
- fruit ripening (promotes food softening and color development)
- senescence
- abscission of leaf, petals, fruit
What does senescence mean
controlled process of growing old and redistribution of nutrients to growing parts of the plant
true or false; in some cases senescence is terminated by abscission of the senescencing region
true
what are snorkel genes in rice
- ethylene induced elongation, so rice submerged or floating in water can produce a snorkel to keep pace with rising flood waters ( anaerobic conditions)
How are ethylene mutants detected
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
Where is ethylene normally produced
shoot tip
- to enable seedlings to avoid obstacles when it is germinating and growing
- produced in response to wounding
true or false; ethylene induces a triple response in seedlings
true
What does it mean by triple response
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
What are the commercial uses of ethylene (adding)
- ripening stimulation (tomatoes, bananas)
- induction of abscission prior to mechanical harvest (cherries)
commercial uses of ethylene (blocking or removing it)
- 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
Who discovered Gibberellin and when
Kurosawa
1926
“foolish seedling disease”
How was Gibberellin discovered
compound secreted by fungus Gibberella fujikuroi
- in rice caused excessive shoot elongation, grain poor or absent
- named Gibberellin after the fungus
true or false; there are 80 natural GA molecules made from mevalonate pathway
true
What is the classic role of Gibberellin (GA)
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
What initiated the Green Revolution of the 20th century
- genes controlling GA synthesis
- due to GA mutants
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
What are commercial uses of GA
- parthenocarpic development of fruit gives seedless table grapes
What does parthenocarpy mean
fruit development in the absence of seeds
What are the properties of ABA (abscisic acid)
found in:
- dormant seeds (dried out)
- buds and water stressed tissues such as mature leaves
effects:
not involved in abscission
Where is ABA made from
mevalonate pathway
What are the major roles of ABA
protect the plant from water stress
induces stomatal closure (reduces transpiration and water loss)
what is the ‘ein’ mutant
an ethylene insensitive mutant
- fails to undergo triple response in the presence of ethylene
What is the ‘ctr’ mutant
a constitutive triple response mutant
- undergoes the triple response even in the absence of ethylene
What is the effect of GA3 on the growth of Thomson seedless grapes
looser cluster of larger grapes
What are Brassinosteroids
are steroid molecules similar to cholesterol
and to animal hormones; purified from rapeseed
What is brassinosteroid required for
- required for normal plant development
- stimulate cell division and elongation
