Chemotropism

The growth of a plant part due to chemical stimulus is known as chemotropism

'Chemotropism is growth of organisms such as bacteria and plants, navigated by chemical stimulus from outside of the organism or organism's part. The response of the organism or organism part is termed ‘positive’ if the growth is towards the stimulus, or ‘negative’ if the growth is away from the stimulus.

Chemotropism in plants

PSM V77 D352 The course of the pollen tube in a rock rose

An example of chemo-tropic movement can be seen during the growth of the pollen tube, where growth is always towards the ovules. It can be also written that conversion of flower into fruit is an example of chemotropism.

Fertilization of flowers by pollen is achieved because the ovary releases chemicals that produce a positive chemo-tropic response from the developing pollen tube.[1]

An example of positive and negative chemotropism is shown by a plant’s roots; the roots grow towards useful minerals displaying positive chemotropism, and grow away from harmful acids displaying negative chemotropism.[2][3]

Chemotropism in animals

Another example of chemotropic movement includes the growth of individual neuronal cell axons in response to extracellular signals. These signals guide the developing axon to innervate the correct target tissue.[4] The neuronal growth cones are guided by gradients of chemoattractant molecules emanating from their intermediate or final targets. There is evidence that the axons of peripheral neurons are guided by chemotropism and the directed growth of some central axons is also a chemo-tropic response, it remains to be determined whether chemotropism also operates in the central nervous system. Evidence of chemotropism has also been noted in neuronal regeneration, where chemotropic substances guide the ganglionic neurites towards the degenerated neuronal stump.[5]

Other examples of Chemotropism

The addition of atmospheric nitrogen, also called nitrogen fixation, is an example of chemotropism.

Chemotropism is different from Chemotaxis, the major difference being that chemotropism is related to growth, while chemotaxis is related to locomotion.

See also

References

  1. ↑ Reger, BJ; Chaubal, R; Pressey, R (1992). "Chemo-tropic responses by pearl millet pollen tubes". Sexual plant reproduction. 5 (1): 47–56. doi:10.1007/BF00714557. Retrieved 7 February 2018.
  2. ↑ Henke, Michael; Sarlikioti, Vaia (3 August 2014). "Exploring root developmental plasticity to nitrogen with a three-dimensional architectural model". Plant Soil. 385: 49–62. doi:10.1007/s11104-014-2221-7. Retrieved 9 February 2018.
  3. ↑ Newcombe FC, Rhodes AL (1904). "Chemotropism of Roots". Botanical Gazette. 37 (1): 22–35. doi:10.1086/328441. JSTOR 2465652.
  4. ↑ Tessier-Lavigne, Placzek, Lumsden, Dodd, Jessell (1988). "Chemotropic guidance of developing axons in the mammalian central nervous system". Nature. 336 (6201): 775–8. doi:10.1038/336775a0. PMID 3205306.
  5. ↑ Gu X, Thomas PK, King RH (1995). "Chemotropism in nerve regeneration studied in tissue culture". Journal of Anatomy. 186 (1): 153–63. PMC 1167281. PMID 7649810.


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