Auxin is a plant hormone that controls the growth of the plant neear the tips, shoots and roots.
It controls the response to light (Photoropism), gravity (gravitropism) and moisture.
Auxin is produced in the tips and moves bach to stimulate cell elongation.
If the tip is removed then no auxin is produced and the plant stops growing.
Extra auxxin promotes the growth in the shoot bu inhibits growth in the root.
Plant Hormones- Towards light
When a shoot tip is exposed to light, more auxin accumalates on the side that in the shade than the side in the light.
This makes the cells grow faster on the shaded side so the shoot bends towards thee light.
Plant Hormones- Away from Gravity
When a shoot is growing sideways , gravity produces an unequal distrubution of auxin in the tip, more auxin on the lower side.
This causes the lower side to grow faster, bending the shoot upwards.
Plant Hormones- Towards gravity
A root growing sideways will also have more auxin on its lower side.
But in a root extra auxin inhibits growth . this means the top side will elongate and bend downwards.
Plant Hormones- Towards Moisture
An uneven amount of moisture causes the side facing the more moisture to produce extra auxin.
This inhibits the growth on the bottom side, causing the root to elongate downwards.
PLANT HORMONES IN AGRICULTURE-
Auxin can be spread on to fields to help promote growth.
Auxin can be used to kill weeds, as too much auxin inhibits growth.