Gall

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Kalanchoë infected with crown gall using Agrobacterium tumefaciens.
A detail photo of a crown gall on a Kalanchoë infected with Agrobacterium tumefaciens.
Galls can also appear on skeletal animals and in the fossil record. Two galls with perforations on a crinoid stem (Apiocrinites negevensis) from the Middle Jurassic of southern Israel.

Galls or cecidia are outgrowths on the surface of lifeforms. Plant galls are abnormal outgrowths[1] of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites. Plant galls are often highly organized structures and because of this the cause of the gall can often be determined without the actual agent being identified. This applies particularly to some insect and mite plant galls. In pathology, a gall is a raised sore on the skin, usually caused by chafing or rubbing.[2]

Causes of plant galls[edit]

Insects[edit]

Insect galls are the highly distinctive plant structures formed by some herbivorous insects as their own microhabitats. They are plant tissue which is controlled by the insect. Galls act as both the habitat and food source for the maker of the gall. The interior of a gall can contain edible nutritious starch and other tissues. Some galls act as "physiologic sinks", concentrating resources in the gall from the surrounding plant parts.[3] Galls may also provide the insect with physical protection from predators.[4][5]

Insect galls are usually induced by chemicals injected by the larvae or the adults of the insects into the plants, and possibly mechanical damage. After the galls are formed, the larvae develop inside until fully grown, when they leave. In order to form galls, the insects must seize the time when plant cell division occurs quickly: the growing season, usually spring in temperate climates, but which is extended in the tropics.

The meristems, where plant cell division occurs, are the usual sites of galls, though insect galls can be found on other parts of the plant, such as the leaves, stalks, branches, buds, roots, and even flowers and fruits. Gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall.

Gall-inducing insects include gall wasps, gall midges, gall flies, Agromyzidae aphids (such as Melaphis chinensis, Pemphigus spyrothecae, and Pemphigus betae), scale insects scale insects, and psyllids.

Fungi[edit]

One gall-inducing fungus is Cedar-apple rust. Galls are often seen in Millettia pinnata leaves and fruits. Leaf galls appear like tiny clubs; however, flower galls are globose.

It is worth noting that the fungus Ustilago esculenta associated with Zizania latifolia, a wild rice, produces an edible gall highly valued as a food source in the Zhejiang and Jiangsu provinces of China.[6]

Bacteria and viruses[edit]

Agrobacterium tumefaciens is an example of a gall-causing bacterium.

Other plants[edit]

Mistletoe can form galls on its hosts

Uses[edit]

Galls are rich in resins and tannic acid and have been used in the manufacture of permanent inks (such as iron gall ink) and astringent ointments, in dyeing, and in tanning. A high-quality ink has long been made from the Aleppo gall, found on oaks in the Middle East; it is one of a number of galls resembling nuts and called "gallnuts" or "nutgalls".

The larvae in galls are useful for a survival food and fishing bait; see the Indigenous Australian foods Bush coconut and Mulga apple. Nutgalls also produce purpurogallin.

The gall of Rhus chinensis, Galla chinensi, has long been considered to possess many medicinal properties.[7]

Gallery[edit]

See also[edit]

Footnotes[edit]

  1. ^ [1] Merriam-Webster Online Dictionary, accessed Nov. 16, 2007 ("an abnormal outgrowth of plant tissue usually due to insect or mite parasites or fungi and sometimes forming an important source of tannin")
  2. ^ medical-dictionary.thefreedictionary.com
  3. ^ Larson, K. C., and T. G. Whitham. 1991. Manipulation of food resources by a gall-forming aphid: the physiology of sink-source interactions. Oecologia 88, P.15 – 21.
  4. ^ Weis, A. E., and A. Kapelinski. 1994. Variable selection on Eurosta’s gall size. II. A path analysis of the ecological factors behind selection. Evolution 48, P.734 – 745.
  5. ^ Graham N. Stone and Karsten Schonrogge (2003) The adaptive significance of insect gall morphology. TRENDS in Ecology and Evolution 18(10):512-522
  6. ^ Terrell, E.E. and L.R. Batra. Zizania latifolia and Ustilago esculenta, a grass-fungus association. Economic Botany 36(3):274-285.
  7. ^ Zhang J, Li L, Kim SH, Hagerman AE, Lü J. 2009. "Anti-cancer, anti-diabetic and other pharmacologic and biological activities of penta-galloyl-glucose." Pharm Res 26: 2066–2080.

Further reading[edit]

  • Blanche, Rosalind (2012). Life in a Gall: The Biology and Ecology of Insects that Live in Plant Galls. Collingwood, Vic.: CSIRO Publishing. ISBN 064310643X. 
  • Redfern, Margaret (2011). Plant Galls. London: Collins. ISBN 0002201445. 
  • Russo, Ron (2007). Field Guide to Plant Galls of California and Other Western States. Berkeley, Calif.: Univ. of California Press. ISBN 9780520248854. 

External links[edit]