Skip to main content
Select Source:

geotropism

geotropism (gravitropism) The growth of plant organs in response to gravity. A main root is positively geotropic and a main stem negatively geotropic, growing downwards and upwards respectively, irrespective of the positions in which they are placed. For example, if a stem is placed in a horizontal position it will still grow upwards. It is thought that mobile membrane-bound clusters of starch grains (amyloplasts) sink to the bottom of a plant cell, under the influence of gravity, and somehow create a physiological asymmetry within the cell. This results in differential growth of the upper and lower sides of the cell, and hence upward or downward curvature of the organ concerned, depending on whether it is a root or a shoot. The biochemical mechanisms of this differential growth remain largely unknown, although auxins are required for geotropism in shoots, and also possibly in roots, and there is evidence that calcium ions play a role too. See tropism.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"geotropism." A Dictionary of Biology. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"geotropism." A Dictionary of Biology. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism-1

"geotropism." A Dictionary of Biology. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

geotropism

ge·ot·ro·pism / jēˈätrəˌpizəm/ • n. Bot. the growth of the parts of plants with respect to the force of gravity. The upward growth of plant shoots is an instance of negative geotropism; the downward growth of roots is positive geotropism. DERIVATIVES: ge·o·trop·ic / ˌjēəˈträpik; -ˈtrō-/ adj.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"geotropism." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"geotropism." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/geotropism

"geotropism." The Oxford Pocket Dictionary of Current English. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/geotropism

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

geotropism

geotropism A directional movement of a plant in response to the stimulus of gravity. Primary tap roots show positive geotropism; vertical primary shoots show negative geotropism; horizontal stems and leaves are diageotropic (see diageotropism); and branches and secondary roots at oblique angles are plagiogeotropic.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"geotropism." A Dictionary of Ecology. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"geotropism." A Dictionary of Ecology. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism

"geotropism." A Dictionary of Ecology. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

geotropism

geotropism A directional movement of a plant in response to the stimulus of gravity. Primary tap roots show positive geotropism; vertical primary shoots show negative geotropism; horizontal stems and leaves are diageotropic (see DIAGEOTROPISM); and branches and secondary roots at oblique angles are plagiogeotropic.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"geotropism." A Dictionary of Plant Sciences. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"geotropism." A Dictionary of Plant Sciences. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism-0

"geotropism." A Dictionary of Plant Sciences. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/geotropism-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Geotropism

Geotropism

Geotropism is the term applied to the orientation response of growing plant parts to Earths gravitational field. Roots are positively geotropic, that is, they will bend and grow downwards, towards the center of Earth. In contrast, shoots are negatively geotropic, that is, they will bend and grow upwards, or away, from the surface.

Geotropism can be demonstrated with seedlings grown entirely in darkness. A seedling with its radicle (or seedling root) and shoot already in the expected orientation can be turned upside down, or placed on its side, while kept in darkness. The root will subsequently bend and grow downwards, and the shoot upwards. Because the plant is still in darkness, photo-tropism (a growth movement in response to light) can be eliminated as an explanation for these movements.

Several theories about the manner by which plants perceive gravity have been advanced, but none of them is entirely satisfactory. To account for the positive geotropism of roots, some researchers have proposed that under the influence of gravity, starch grains within the cells of the root fall towards the bottom of the cell. There they provide signals to the cell membrane, which are translated into growth responses.

However, there have been many objections to this idea. It is likely that starch grains are in constant motion in the cytoplasm of living root cells, and only sink during the process of fixation of cells for microscopic examination. Roots can still be positively geo-tropic and lack starch grains in the appropriate cells.

A more promising hypothesis concerns the transport of auxin, a class of plant-growth regulating hormones. Experiments since 1929 have shown that auxin accumulates on the down side of both shoots and roots placed in a horizontal position in darkness. This gradient of auxin was believed to promote bending on that side in shoots, and to do the opposite in roots. Confirmation of the auxin gradient hypothesis came in the 1970s. When seeds are germinated in darkness in the presence of morphactin (an antagonist of the hormonal action of auxin), the resulting seedlings are disorientedboth the root and shoot grow in random directions. Auxin gradients are known to affect the expansion of plant cell walls, so these observations all support the idea that the transport of auxin mediates the bending effect that is an essential part of the directional response of growing plants to gravity.

See also Gravity and gravitation.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Geotropism." The Gale Encyclopedia of Science. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"Geotropism." The Gale Encyclopedia of Science. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/geotropism

"Geotropism." The Gale Encyclopedia of Science. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/geotropism

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Geotropism

Geotropism

Plants can sense the Earth's gravitational field. Geotropism is the term applied to the consequent orientation response of growing plant parts. Roots are positively geotropic, that is, they will bend and grow downwards, towards the center of the Earth . In contrast, shoots are negatively geotropic, that is, they will bend and grow upwards, or away, from the surface.

These geotropisms can be demonstrated easily with seedlings grown entirely in darkness. A seedling with its radicle (or seedling root) and shoot already in the expected orientation can be turned upside down, or placed on its side, while kept in darkness. The root will subsequently bend and grow downwards, and the shoot upwards. Because the plant is still in darkness, phototropism (a growth movement in response to light ) can be eliminated as an explanation for these movements.

Several theories about the manner by which plants perceive gravity have been advanced, but none of them is entirely satisfactory. To account for the positive geotropism of roots, some researchers have proposed that under the influence of gravity, starch grains within the cells of the root fall towards the "bottom" of the cell . There they provide signals to the cell membrane , which are translated into growth responses. However, there have been many objections to this idea. It is likely that starch grains are in constant motion in the cytoplasm of living root cells, and only "sink" during the process of fixation of cells for microscopic examination. Roots can still be positively geotropic and lack starch grains in the appropriate cells.

A more promising hypothesis concerns the transport of auxin, a class of plant-growth regulating hormones . Experiments since 1929 have shown that auxin accumulates on the "down" side of both shoots and roots placed in a horizontal position in darkness. This gradient of auxin was believed to promote bending on that side in shoots, and to do the opposite in roots. Confirmation of the auxin gradient hypothesis came in the 1970s. When seeds are germinated in darkness in the presence of morphactin (an antagonist of the hormonal action of auxin), the resulting seedlings are disoriented—both the root and shoot grow in random directions. Auxin gradients are known to affect the expansion of plant cell walls, so these observations all support the idea that the transport of auxin mediates the bending effect that is an essential part of the directional response of growing plants to gravity.

See also Gravity and gravitation.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Geotropism." The Gale Encyclopedia of Science. . Encyclopedia.com. 10 Sep. 2018 <http://www.encyclopedia.com>.

"Geotropism." The Gale Encyclopedia of Science. . Encyclopedia.com. (September 10, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/geotropism-0

"Geotropism." The Gale Encyclopedia of Science. . Retrieved September 10, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/geotropism-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.