Plant Tropisms

• Auxins are produced by the shoot apical meristem, young leaves, buds, flowers, fruits, and roots.
• In the shoots, auxins promote cell elongation; more auxin = more cell elongation = more growth.
• In the roots auxins inhibit cell elongation; less auxin = less cell elongation = less growth.
• Role in phototropism: Auxin accumulates on the shaded side of a stem, promoting elongation & causing the stem to bend towards the light source (positive phototropism)
• Role in gravitropism: Auxin accumulates on the lower side of a stem in shoots, causing it to grow upwards (negative gravitropism)
• Role in gravitropism: Auxin inhibits growth on the lower side of the root, allowing it to grow downwards in the direction of gravity (positive gravitropism).
• Gravitropism (geotropism) is the growth response to gravity. A negative response grows away and a positive response grows towards gravity.
• Phototropism is the growth response from the source of light. A negative response bends away from light and a positive response grows towards the light source.