auxins + photochromes - topic 8 Flashcards
what do plants use instead of a nervous system to send messages
chemicals
name the two types of tropism and state what they mean
photo - response to light
geo - response to gravity
what is the most common type of auxin
IAA
what does IAA do and how is it transported?
- it stimulates transcription and cell elongation
- transported by diffusion and active transport
- longer distances it is transported in the phloem
describe how phototropism is achieved
- when sun shines on one side of a plant
- IAA moves to shady side
- it is unevenly distributed
- stimulates cell elongation on this side
shaded side grows causing stem to grow towards light
why does phototropism occur?
more of the plant is in the light so it can photosynthesise
describe how positive geotropism is achieved
- auxins move to bottom side of the root due to gravity
- auxin inhibits growth so bottom grows less
- root grows down
describe how negative geotropism is achieved
- auxins move to bottom side of the stem due to gravity
- auxin stimulates growth so bottom grows more
- stem grows up
name the two types of photochromes
pfr - absorbs far red light
pr- absords red light
what happens to photochromes in the sunlight?
- sunlight has more red light
- causes pr -> pfr
- pfr accumulates
describe what happens to photchromes in the dark
pfr converted back to pr as no red light available
describe how long day plants flower
- flowers when nights are short
- increased pfr stimulates flowering
- because cause expression of genes that activate flowering
- gene is transcribed and translated
- flowers are produces rather than stems and leaves
describe how short day plants flower
- flower when darkness >12hrs
- pfr -> pr
- pfr inhibits flowering
- a single flash of light will negate effect of dark period
EQ. Explain why a plant would be grown in agar containing IAA (3)
- cause cell elongation
- increased transcription of cells / increased plasticity of celll wall
- stimulates roots tp grow/ stimulates growth of plants
EQ Describe the role of IAA (auxin) in the phototropic response of plants.(4)
- IAA produced inn the tip of shoots
- IAA accumalates on shaded side of the plant
- stimulated cell elongation
- causing shoot to grow towards light source
How do auxins bring about responses for gene expression ?
- Auxins bind to protein receptors in target cells
- activates second messenger signal molecules
-which activate transcription factors - start transcription
- genes produce proteins for cell devision, expansion and differentiation
How does auxin bring about cell expansion
- stimulated proton pump
- causes acidification of cell wall
- activation of expansin enzymes
- bind between cellulose microfibrils break (wall becomes more plastic)
- increased water uptake = elongation
