Auxins Flashcards
What is IAA
Indoleacetic acid, an important auxin produced in tips of shoots in flowering plants
What happens when IAA enters the nucleus of a cell
It’s able to regulate the transcription of genes related to cell elongation and growth
How does IAA move around plant
Moves by diffusion from tip of roots and shoots to neighbouring plants and active transport short distances and via phloem over longer distances
Where does IAA accumulate
On darker side of roots (furthest from light) and shoots by diffusing away from light source, uneven distribution of IAA means uneven growth of the plant
How does shoot show phototropism
IAA diffuses away from light source, cells elongate on darker side furthest from light source faster than lighter and shoot bends towards light
How does root show phototropism
IAA accumulates on darker side by diffusing away from light source so growth inhibited (inhibits growth in roots on side furthest from light source) so root bends away from light downwards
How does root show geotropism
IAA diffuses away from light source and accumulates on side furthest from light source and inhibits growth here so root bends downwards
What are phytocromes
Photoreceptors that detect light found in leaves seeds roots and stem
What do phytocromes do
Control range of responses eg plants flower in dif seasons depending on how much day light there is at that time of year
What are the two states phytocromes exist in
PR state: absorbs red light at wavelengths of 660nm
PFR state: absorbs far red light at wavelength of 730nm
What happens when PR exposed to red light
Quickly converted into PFR
What happens when PFR exposed to far red light
Quickly converted into PR
What happens when PFR in darkness
Slowly converted into PR
What type of light does daylight contain more of and what does this mean
Contains more red than far-red light so more PR converted into PFR than PFR converted to PR
What do different amounts of PR and PFR control
The responses to light by regulating the transcription of genes involved in these responses
Why do some plants flower in summer
When nights short there’s not much time for PFR to be converted back into PR so PFR builds up and genes involved in flowering are transcribed as in some plants high levels of PFR stimulates flowering
Which cells elongate
Those across the zone of elongation due to auxins moving down shoot tip
How does cells elongate
Cell walls ‘loosen’ which go on to take in water by osmosis and stretch, protons pumped into the cell wall from the cell cytoplasm disrupt the bonds between cellulose molecules allowing the cell wall to be stretched
How does shoot show geotropism when sideways
IAA diffuses away from light source and accumulates on side furthest from light source, causes cell elongation on underside so shoot grows upwards
