tropism

[From -TROPISM.]

(TRO-piz-uhm)

noun
The turning or bending (typically by growth instead of movement) of an organism in response to an external stimulus.

Etymology
From Greek tropos (turning). Ultimately from Indo-European root trep- (to turn) that also gave us troubadour, tropic, entropy, and contrive

If you've ever noticed a plant bending towards the light, you've seen an example of tropism. The term is usually applied to plants. The response to a stimulus could be positive or negative: towards or away from the stimulus. Some examples of stimuli are light (phototropism), gravity (geotropism), heat (thermotropism), touch (thigmotropism), and water (hydrotropism).
Darwin and his son Francis demonstrated that the tip of the plant detected light and if you covered just the tip, the plant would grow straight, not toward the light.
The word tropism is related to trope, the term for rhetorical devices such as metaphor and irony. The idea is that the words in those rhetorical devices are turned in a special way.
garg AT wordsmith.org

Maureen Dowd earned her Alt-Clicks with her attack on Judy Miller. The column peaked with:

"She more than earned her sobriquet 'Miss Run Amok.'"

after opening with:

"I've always liked Judy Miller. I have often wondered what Waugh or Thackeray would have made of the Fourth Estate's Becky Sharp. The traits she has that drive many reporters at The Times crazy - her tropism toward powerful men, her frantic intensity and her peculiar mixture of hard work and hauteur - have never bothered me. I enjoy operatic types."

Tropism, hauteur and sobriquet all finished in the Top 5 Alt-Clicks for the day.

Link: Woman of Mass Destruction

Posted October 23, 2005.

See our Word Overheard blog to see interesting uses of strange words.

Tropism is the movement of a plant in response to a stimulus. The categories include:

Chemotropism-a response to chemicals by plants in which incurling of leaves may occur.

Geotropism or gravitropism-a response to gravity in which the plant moves in relation to gravity. Shoots of a plant are negatively geotropic (growing upward), while roots are positively geotropic (growing downward).

Hydrotropism-a response to water or moisture in which roots grow toward the water source.

Paraheliotropism-a response by the plant leaves to avoid exposure to the sun.

Phototropism-a response to light in which the plant may be positively phototropic (moving toward the light source) or negatively phototropic (moving away from the light source). Main axes of shoots are usually positively phototropic, whereas roots are generally insensitive to light.

Thermotropism-a response to temperature by plants.

Thigmotropism or haptotropism-a response to touch by the climbing organs of a plant. For example, the plant's tendrils may curl around a support in a spring-like manner.

A growth response in a nonmotile organism elicited by an external stimulus, and either toward (positive tropism) or away from (negative tropism) the stimulus; used as a word element combined with a stem indicating nature of the stimulus (e.g. phototropism) or material or entity for which an organism (or substance) shows a special affinity (e.g. neurotropism).

A reaction to an external stimulus, such as light. See also phototropism; geotropism.

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Phycomyces, a fungus, exhibiting phototropism

A tropism (from Greek, tropos, to turn) is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus (as opposed to nastic movements which are non-directional responses). Viruses and other pathogens also affect what is called "host tropism" or "cell tropism" in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, or specific cell types within those species. The word tropism comes from the Greek trope ("to turn" or "to change"). Tropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to light) and may be either positive (towards the stimulus) or negative (away from the stimulus).

Tropisms are typically associated with plants (although not necessarily restricted to them). Where an organism is capable of directed physical movement (motility), movement or activity in response to a specific stimulus is more likely to be regarded by behaviorists as a taxis (directional response) or a kinesis (non-directional response).

In English, the word tropism is used in sometimes derisive way to indicate an action done without cognitive thought: However, "tropism" in this sense has a proper, although non-scientific, meaning as an innate tendency, natural inclination, or propensity to act in a certain manner.

Ecotropism or ecotropic from Eco, meaning the hearth (from which words like ecology and enonomy are derived, and "Tropic," meaning to turn towards. The basic philosophy of ecotropism and ecotropics argues that to be healthy human culture itself must inhabit an ecological niche, and thereby, relate appropriately with all the co-evolving forces, organic and inorganic. In short, human culture must turn towards the environment for a sustainable and meaningful future.

Curiously, the scientific community has latched onto this word to formulate the exact inverse. Here Ecotropics indicates that a pathogen like a virus or a bacterium has a narrow host range and can infect only one or a small group of species or cell culture lines.

Types of tropisms

• Chemotropism, movement or growth in response to chemicals
• Gravitropism (or geotropism), movement or growth in response to gravity
• Heliotropism, movement or growth in response to sunlight
• Phototropism, movement or growth in response to lights or colors of light
• Thermotropism, movement or growth in response to temperature
• Thigmotropism, movement or growth in response to touch or contact
• Host tropism or cell tropism, the host range of pathogens
  • Ecotropism, limited host range (e.g. infects only one species or cell type)
  • Amphotropism, wide host range (e.g. infects many species or cell types)
  • HIV tropism, the means of entry into cells used by a given strain of HIV
  • Neurotropism, a virus that preferentially infects the host's nervous system.

See also

• Rapid plant movement

v • d • e Tropism Chemotropism · Gravitropism · Hydrotropism · Heliotropism · Phototropism · Thermotropism · Thigmotropism

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