Tropism
/ˈtroʊpɪzəm/
Definition
Tropism is a plant biological response in which growth changes direction because of an outside stimulus. Unlike a temporary movement, it involves unequal growth, so the bending is usually lasting. Stems often show positive phototropism by growing toward light, while roots may show positive gravitropism by growing downward in response to gravity. Other forms respond to touch, water, or chemicals.
Biological Role
- Directional growth control: In plants, tropism helps shoots and roots place themselves where light, water, and physical support are more favorable, which improves access to resources without moving the whole organism.
- Hormone-driven bending: Many responses depend on uneven distribution of auxin, a plant growth hormone, across an organ. Cells on one side elongate more than the other, causing a curve.
- Different responses in roots and shoots: Shoots commonly bend toward light, while roots often grow downward and may grow toward moisture. These contrasting patterns help divide aboveground and belowground functions.
- Practical value indoors and in propagation: Observable bending can explain leaning houseplants, one-sided seedlings, and climbing stems that wrap supports. Rotating containers or providing even light can reduce uneven growth in some situations.
Related Terms
Phototropism
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Geotropism
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Hydrotropism
Hydrotropism is a plant growth response to moisture gradients, most often seen in roots bending toward areas with more…
Thigmotropism
Thigmotropism is a directional growth response to touch or physical contact. In plants, it occurs when contact with a…
Nastic movement
Nastic movement describes a plant movement triggered by a stimulus such as touch, light, temperature, or day-night…
Photoperiodism
Photoperiodism describes a plant’s biological response to the relative lengths of day and night. It is a timing…
Phytochrome
Phytochrome is a light-sensing plant pigment protein, or photoreceptor, that detects red and far-red light. It helps…