plant hormones

• auxin is a plant hormone that controls growth near tops of shoots and roots
• auxin controls plant growth in response to light (phototropism) and gravity (geotropism)
• auxin is produced in the tips and moves backwards to stimulate cell elongation which occurs in cells just behind the tips
• if the tip of a shoot is removed, no auxin is available and the shoot may stop growing
• extra auxin promotes growth in the shoot but inhibits growth in the root
• when a shoot tip is exposed to light, more auxin accumulates on the side that’s in the shade. this makes cells elongate faster on the shaded side, so the shoot bends to the light
• I hen a shoot is growing sideways, gravity produces unequal distribution of auxin in the tip, with more auxin on the lower side. this causes the lower side to grow faster, bending the shoot up
• auxins can kill weeds. weeds normally have broad leaves, so some weedkillers have been developed using auxins which only affect broad leaved plants. this disrupts their growth patterns and kills them.
• auxins can cause cuttings to grow. if you add rooting powder (contains auxins), they will produce roots and start growing. this means growers can clone good plants quickly
• tissue culture can be used to grow clones of a plant from a few of its cells. to do this, auxins and nutrients are added to the growth medium to stimulate cells to divide to form roots and shoots