Plant Hormones Flashcards
(66 cards)
1
Q
functions of gibberellins
A
- germination of seeds
- elongation of plant stems (effect length of internodes)
2
Q
how were gibberellins discovered?
A
- rice seedlings were infected with the Gibberella fungus
- they grew extremely tall and thin
3
Q
how did scientists test their discovery of gibberellins?
A
- isolated gibberellins produced by Gibberella fungus
- found that plants produce the same compounds
4
Q
uses of gibberellins and why is it useful?
A
- breeding dwarf plants where gibberellin synthesis pathway is interrupted
- reduces waste and less vulnerable to damage by weather and harvesting
- we eat fruits and leaves not the stems so it’s more financially beneficial
5
Q
what activates gibberellelins to be produced in seeds?
A
seed absorbs water which activates embryo to produce gibberellins
6
Q
how do gibberellins stimulate seed germination?
A
- storage proteins are broken down into amino acids
- amino acids used to make amylase
- amylase hydrolyses starch to maltose
- maltose is hydrolised to glucose
- glucose is respired to produce ATP
- ATP is used as an energy store to build materials to grow and break out of the seed coat
7
Q
structure of a seed
A
- outer seed coat
- layer containing protein
- starchy food store inside
- embryo takes up about a third of the seed
8
Q
which part of the seed produces gibberellins?
A
embryo
9
Q
antagonistic plant hormones example (short explanation of how they act as antagonistic)
A
- gibberellins switch on genes coding for amylases and proteases
- ABA acts as an antagonist
10
Q
what hormone concentrations determine seed germination?
A
relative concentrations of gibberellins and ABA
11
Q
what are the names for dicot and monocot seeds?
A
dicot - cotyledons
monocot - endosperm
12
Q
two pieces of evidence for gibberellins
A
- when the genes to produce gibberellins are removed the seeds don’t germinate but when gibberellins are applied externally the seeds germinate normally
- when gibberellin biosynthesis inhibitors are applied the seeds don’t germinate but when inhibition is removed the seeds germinate normally
13
Q
response to low temperature in plants
A
solutes (e.g. polysaccharides, amino acids and proteins) are actively pumped into the cytoplasm and vacuole sap to lower the freezing point of the cell
14
Q
how are mechanisms in response to abiotic stress in plants controlled?
A
- transcription factors
- genes suppressed or activated in response to sustained temperature or daylight length changes
15
Q
why is abscission important?
A
- plant is more likely to be damaged or blown over by wind with more leaves
- rate of respiration may be higher than rate of photosynthesis meaning glucose is used up faster than it can be produced OR glucose produced is not enough to prevent leaves freezing
–> losing leaves can lower energy demand
16
Q
name for the sensitivity to lack of light
A
photoperiodism
17
Q
uses of photoperiodism
A
- dormancy
- flowering
- tuber formation
18
Q
how is light intensity detected?
A
- phytochrome pigment
- Pr and Pfr absorb different types of light
- ratio of Pr : Pfr changes depending on light intensity
19
Q
what hormones do falling light levels affect?
A
- decrease auxin concentration
- this increases the production of ethene
20
Q
how does ethene cause abscission?
A
- ethene switches on genes in abscission zone
- production of enzymes which digest and weaken cell walls in separation layer
- vascular bundles seal up
- fatty material deposited to form protective layer from pathogens
- cells deep in separation zone retain water, swell and put pressure on weak cell walls
- wind finishes off the process
21
Q
two zones involved in abscission
A
- protective layer
- separation zone
22
Q
three responses to herbivory
A
- alkaloids
- pheromones
- folding in response to touch
23
Q
what are alkaloids? name three examples
A
- bitter tasting, nitrogenous compounds
- drugs affecting metabolism
- caffeine, nicotine, morphine
24
Q
pheromones
A
- released when under attack
- stimulate production of things like callose
25
how do plants fold in response to touch?
- K+ actively pumped into certain cells
- lowers water potential of the cells
- water diffusers inter sales fire osmosis
26
how does folding in response to touch help defend against herbivory?
- frighten large herbivores
- dislodge insects
27
when do stomata open?
when temperatures and water availability are high
28
what hormone stimulates stomatal control?
ABA (abscisic acid)
29
what stimulates ABA production?
levels of soil water fall
30
where is ABA produced?
- leaves
- roots
31
how does ABA close stomata?
- ABA produced in leaves and/or roots
- transported to leaves
- binds to plasma membrane receptors of guard cells
- changes ionic concentration
- Ψ lowers
- water diffuses into guard cells via osmosis
- guard cells become turgid (close stomata)
32
what happens to the stomata when guard cells are flaccid or turgid?
turgid - stomata closed
flaccid - stomata open
33
which tropism cannot be positive or negative?
chemotropism
34
five tropisms
- phototropism
- geotropism
- chemotropism
- hydrotropism
- thigmotropism
35
which tropisms can only be positive?
- hydrotropism
- thigmotropism
36
stimulus of geotropism
gravity
37
stimulus of thigmotropism
touch
38
example of chemotropism
pollen tubes grown down style towards ovary
39
example of thigmotropism
pea spindles curl around pole to help grow upwards
40
positive vs negative geotropism
- positive geotropism stimulates roots to grow down towards stimulus
- negative geotropism stimulates shoots to grow away from the force of gravity
41
define tropisms
- directional growth responses of plants caused by an external stimulus
- direction of response is determined by the stimulus direction
42
how are plant hormones transported?
- active transport
- diffusion
- mass flow
43
what does ABA stand for?
abscisic acid
44
how do auxins stimulate phototropism?
- auxin actively transports H+ out of cell to lower pH of surroundings
- decrease in pH activates cellulase
- cellulose hydrolyses cellulose
- loosens the binding of cellulose fibres in the cell wall (more permeable)
- water diffuses into cell via osmosis
- cell expands
45
what activates cellulase?
decrease in pH
46
cellulase function
hydrolyse cellulose
47
what happens to auxin in mature cells? and what is the effect of this?
- auxin is destroyed
- surrounding pH increases
- cellulase inactivated
- cell retains a fixed shape
48
what is IAA short for?
auxin
49
coleoptile
pointed protective sheath covering the emerging sheet in monocotyledons such as grasses
50
functions of auxin
- cell elongation (positive phototropism and positive geotropism)
- apical dominance
51
evidence for apical dominance
- apical bud removed so no auxins are released
--> lateral shoots begin to grow freely and quickly
- auctions artificially applied again and apical dominance is restored
52
advantages of apical dominance
- survival advantage
- out compete other plants for light
- more light means faster rate of photosynthesis so more sugars can be produced which increases rate of respiration so more ATP can be produced leading to more growth
53
difference between auxins in roots and shoots
- increased auxin concentration decreases cell elongation in roots
- increased auxin concentration increases cell elongation in shoots
54
how do auxins stimulate positive geotropism?
- root tip produces auxins
- auxins diffuse to the lower side of root due to gravity
- auxins diffuse along lower side of root
- cell elongation is inhibited so the lower side grows slower than the upper side
- root curves downwards
55
synergism
hormones work together to give a greater response than they would on their own
56
antagonism
balance of hormones determines the response (one stimulates and another inhibits)
57
commercial uses of auxins
- flower production
- hormone rooting powder
- seedless fruit
- herbicides/weed killers
58
commercial uses of gibberellins
- fruit production
- delay ripening and ageing in fruit
59
commercial uses of cytokinins
- tissue culture
- prevent aging of ripened fruit
60
cytokinins function
promote mitosis
61
commercial uses of ethene
- fruit ripening
- fruit drop
- lateral growth
62
how does ethene help in the ripening of fruits? and why is this beneficial?
- fruits continues to ripen after harvest
- allows fruit to be harvested as soon as it matures even if it's not ripe yet (time efficient)
- unripe fruit is less easily damaged during transport
- fruit ripens at the same rate (prevent waste)
63
commercial uses of hormone rooting powders
- stimulate growth of roots in micropropagation
64
what does hormone rooting powder contain?
auxins
65
how can synthetic auxins be used as weedkillers?
- synthetic auxins are absorbed by plants and their metabolism is affected
- growth rate increases and becomes unsustainable leading to death
66
benefits of synthetic auxins
- kill weeds to reduce competition with crops
- relatively simple and cheap
- low toxicity to mammals
- selective (in respect to which plants they affect)
