Plant Growth Hormones and their Uses

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Plant Hormones and Growth
Auxins are plant hormones which control growth at the tips of roots and shoots
Auxins are dissolved in a solution of water
Auxins stimulates cell elongation
Inhibits growth in the roots
Promotes growth in the shoot
Auxins use light responses from light (phototropism) and gravity (geotropism)
Shoots are positively phototropic ­ Grow towards light. More auxin is produced on the
side in the shade ­ cells elongate and the shoot grows towards the light
Shoots are negatively geotropic ­ Grow away from gravity. A shoot grows sideways and
gravity produces more auxin on the bottom end which causes it to shoot upwards
Roots are negatively phototropic ­ Grow towards gravity. The shoot will have more
auxins on the bottom side but the auxin will inhibit growth so it grows towards the ground
Roots are positively geotropic ­ Grow away from light. More auxins are found on the
shaded side. The cell elongation is inhibited and grows back into the ground
Plants need light and water for photosynthesis and they use tropisms to be near those
sources. They can either grow away or to the stimulus which is controlled by auxins.
Auxins are made in the roots and shoots of a plant and diffuse to the other parts
Auxins change the rate of elongation in plant cells ­ which controls growth. Cells in
the shoots grow more and roots grow less: auxins have the opposite effects on the
roots and shoots
Auxins accumulate on the shaded side of a plant or it bends towards/away from

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Uses of Plant Hormones:
Selective Weed killers:
Attacks some plants but not others ­ only affects broad leaved plants
Contains a growth hormone which makes them grow too quickly
Rooting Powder:
Provides roots to stem cuttings quickly
Allows clones of plants to be make very quickly
Controlling Fruit Ripening:
Plant hormones slow down ripening while in transport
Less damaged when packaged
Plant hormones are used to ripen the fruit when in the shop
Stops seeds germinating until conditions have changed
`Gibberelin' breaks the dormancy…read more


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