topic 9.3 Flashcards
1
Q
what is auxin
A
- auxin is a plant hormone that plays a role in the cell elongation, promotion of root growth and suppression of lateral buds to promote apical dominance
2
Q
what effect do auxins have on cell walls
A
- they affect the ability of cell walls to stretch
3
Q
where are auxins synthesized and how do they travel down a plant
A
- synthesised in the meristems
- diffuse down the plant
4
Q
cell elongation
A
- auxin binds to receptors on cell membrane
- hydrogen ion pump is activated so pH decreases
- enzyme breaks bonds between cellulose microfibrils
- water enters by osmosis and cell elongates
5
Q
how does elongation stop
A
- eventually enzymes destroy the auxin’s - stopping elongation
6
Q
root growth
A
- auxin’s actively transported down the plant towards the roots
- the more the auxin’s are transported down the stem, the more the root growth
7
Q
what are tropisms
A
- they are directional growth responses to specific environmental cues
8
Q
what are the two type of tropisms
A
- phototropism
- gravitropism
9
Q
phototropism
A
- plant shoots grow toward light unilaterally
- positive phototropism
- plant roots grow away from light
- negative phototropism
when light hits the shoots of the plant, auxin’s move to shaded side and promote elongation towards the light
10
Q
gravitropism
A
- plant shoots grow against gravity
- negative gravitropism
- plant roots grow in the direction of gravity
- positive gravitropism
auxin’s move down the plant and promote elongation
11
Q
what are cytokinins
A
- cytokinins promote cell division in apical meristems and cambium, promote lateral bud development and work with ethene in abscission of leaves
12
Q
high levels of cytokinin?
A
- keeps the leave healthy and alive
13
Q
low levels of cytokinin
A
- leaf dies and falls
14
Q
gibberellins
A
- stimulate elongation of cells, growth of fruit and breaking dormancy in seeds
15
Q
how do gibberellins germinate
A
- the embryo secretes gibberellins that diffuse into the aleurone layer
- aleurone layer produces amylase to digest the carbohydrate stores of endosperm
- products from endosperm are used to make new cells and germinate
16
Q
synergy
A
- when two hormones work together complimenting each other and giving greater response together
17
Q
antagonism
A
- when two hormones have opposite effects and the balance between then determines response
18
Q
apical dominance
A
- this is when one lead shoot grows bigger and faster than the others
19
Q
auxin - apical dominance
A
- high auxin levels from dominant shoot inhibits lateral bud growth
- when the shoot grows further away, the inhibition of auxin is reduced (cytokinin dominant)
- as level of auxin reduces down the stem, lateral buds start to develop
- if main shoot is removed, source of auxin is removed so cytokinin is dominant → lateral buds can grow
20
Q
cytokinin and auxin work…
A
antagonistacally
21
Q
what is phytochrome
A
- a plant pigment that reacts differently with different type of light and affects the responses of plants
22
Q
what are the two forms of phytochrome pigment
A
Pr and Pfr
23
Q
what converts Pr to Pfr
A
red light
24
Q
what converts Pfr to Pr
A
far red light
25
how is Pr converted to Pfr
- a seedling germinates and makes Pr
- it breaks through the surface of the soil and is exposed to red light
- this causes Pr to be converted Pfr
26
when do short day plants flower
autumn
27
short day plants
- short days and long nights
- not a lot of light
- **high levels of Pfr inhibit flowering**
- longer nights so most Pfr is converted to Pr
- Pfr levels **fall**
- hence flowering can occur
- short daytime = Pr →Pfr; Pfr inhibits flowering
- long nightime = Pfr
## Footnote
flower in spring and autumn
28
long day plants
- long days and short nights
- lots of light
- high levels of Pfr stimulate flowering
- short nights so little Pfr is converted back to Pr
- Pfr levels maintained are high
- hence flowering occurs
- long daytime = Pr → Pfr; Pfr stimulates flowering
- nightime = more Pr than Pfr
## Footnote
flower in summer
29
photomorphogenesis
- the process by which the form and development of a plant is controlled by the levels of and type of light
30
ehat are the two forms phytochrome converts between
- biologically inactive Pr which absorbs red light
- biologically active Pfr absorbs far red light
31
etiolated plant
- all phytochrome is in the Pr form
- these grow rapidly using food reserves in attempt to reach light
- tall and thin
- small yellow leaves
- little root growth
32
what does phytochrome control
- the changes that take place when a plant becomes etiolated
- the reverse when it reaches light when germinating seeds break through soil are controlled by phytochrome
33
germination - phytochrome
- phytochrome is synthesised as Pr
- when a seedling energes from a seed underground it only contains Pr as there is no light to produce Pfr
- seedling shows characteristics of etiolation
- stem lengthens quickly, doesn't thicken, little root growth, no leaf growth, no chloropyll
- when shoot breaks through surface, stem elongation slows down, leaves open, chloropyll forms, seedling starts to photosynthesise
- changes are caused by Pfr
34
how does phytochrome act as a transcription factor
- involved in switching genes on and off in the nucleus of plant cells
35
phytochrome as a transcription factor
- Pr is converted to Pfr in the presence of light
- Pfr moves into the nucleus through pores in the nuclear membrane
- Pfr binds to protein phytochrome interacting factor, PIF3, in nucleus
- PIF3 **activates gene transcription** when it is bound to Pfr
- genes activated by PIF3 control different aspects of growth and development in plants
36
what is PIF3
- PIF3 is a transcription factor which only binds to Pfr
