Summary
Directional growth in response to gravity, with roots growing down and shoots growing up.
In depth
Statoliths (starch-filled amyloplasts) in root cap cells settle and trigger auxin redistribution. High auxin inhibits root elongation on the lower side so the root bends down; in shoots it promotes elongation, so they bend up.
Gravity sensing by statoliths leads to PIN protein repositioning and auxin redistribution. Roots show positive gravitropism and shoots negative.
Common mistake: plants do not 'know' up from down using a nervous system; it is a cellular response to sedimenting starch grains.
Roots show positive gravitropism and shoots negative. Starch-filled amyloplasts (statoliths) in columella cells of the root cap sediment, and this triggers redistribution of auxin by PIN3 so that the lower side of a horizontal root has more auxin, slows growth and bends the root downward. Shoots use endodermal cells as sensors and elongate more on the lower side.
Experiments on the International Space Station showed that plants orient in the absence of gravity using light, and clinostats rotate plants to cancel gravity. Gravitropism helps seedlings find soil and leaves reach light. Lateral organs often grow at set angles (gravitropic setpoint).
Remember: removing the root cap abolishes the gravity response, which shows where sensing happens.
Frequently asked questions
What is Gravitropism?
Directional growth in response to gravity, with roots growing down and shoots growing up.
Which area of biology covers Gravitropism, and how advanced is it?
Gravitropism is one of the 56 topics in Plant Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Auxin and Phototropism, Phytochrome Signalling, Plant Hormones.
Can you give an example of Gravitropism?
Plants grown in space show altered gravitropism.
What should I learn before Gravitropism?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to Gravitropism. Intermediate topics assume the Beginner vocabulary.
What topics are related to Gravitropism?
The closest topics to Gravitropism are Auxin and Phototropism, Phytochrome Signalling, Plant Hormones, Translocation. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Gravitropism?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Gravitropism. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is Gravitropism different from Auxin and Phototropism?
Gravitropism: Directional growth in response to gravity, with roots growing down and shoots growing up. Auxin and Phototropism: Auxin moves to the shaded side of a shoot, causing cells there to elongate so it bends toward light. Read both side by side and note what each one explains.
What is a common mistake about Gravitropism?
Plants do not 'know' up from down using a nervous system; it is a cellular response to sedimenting starch grains.
How should I study Gravitropism step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Auxin and Phototropism and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.