crown gall


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crown gall:

see gallgall,
abnormal growth, or hypertrophy, of plant tissue produced by chemical or mechanical (e.g., the rubbing together of two branches) irritants or hormones. Chemical irritants are released by parasitic fungi, bacteria, nematode worms, gall insects, and mites.
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Crown gall

A neoplastic disease of primarily woody plants, although the disease can be reproduced in species representing more than 90 plant families. The disease results from infection of wounds by the free-living soil bacterium Agrobacterium tumefaciens which is commonly associated with the roots of plants.

The first step in the infection process is the site-specific attachment of the bacteria to the plant host. Up to half of the bacteria become attached to host cells after 2 h. At 1 or 2 weeks after infection, swellings and overgrowths take place in tissue surrounding the site of infection, and with time these tissues proliferate into large tumors (see illustration). If infection takes place around the main stem or trunk of woody hosts, continued tumor proliferation will cause girdling and may eventually kill the host. Crown gall is therefore economically important, particularly in nurseries where plant material for commercial use is propagated and disseminated.

Crown gall on peachenlarge picture
Crown gall on peach

Unlike healthy normal cells, crown gall tumor cells do not require an exogenous source of phytohormones (auxins and cytokinin) for growth in culture because they readily synthesize more than sufficient quantities for their own growth. They also synthesize basic amino acids, each conjugated with an organic acid, called opines. The tumor cells also grow about four times faster and are more permeable to metabolities than normal cells.

These cellular alterations, such as the synthesis of opines and phytohormone regulation, result from bacterial genes introduced into host plant cells by A. tumefaciens during infection. Although it is not understood how these genes are introduced into the plant cell, the genes for the utilization of these opines and for regulating phytohormone production have been found to be situated on an extrachromosomal element called the pTi plasmid. This plasmid, harbored in all tumor-causing Agrobacterium species, also carries the necessary genetic information for conferring the tumor-inducing and host-recognition properties of the bacterium.

Crown gall is consequently a result of this unique bacteria-plant interaction, whereby A. tumefaciens genetically engineers its host to produce undifferentiated growth in the form of a large tumor, in which there is the synthesis of a unique food source in the form of an opine for specific use by the bacterial pathogen. See Bacterial genetics, Genetic engineering, Plant hormones, Plant pathology

crown gall

[′krau̇n ‚gȯl]
(plant pathology)
A bacterial disease of many plants induced by Bacterium tumefaciens and marked by abnormal enlargement of the stem near the root crown.
References in periodicals archive ?
crown gall, removing soil from around infected plant roots to assure galls and infected roots are discarded before planting in the same area -- Looking for protective sprays that will control foliar and flower diseases (powdery mildew and Botrytis) that are effective and are environmentally safe -- Raking and destroying fallen leaves from around rose bushes during and at the end of each growing season to avoid continued spread and over- wintering of disease
Crown gall tumor disc bioassay: a possible aid in the detection of compounds with antitumor activity.
Agrobacterium radiobacter k1026 is a biopesticide used to control the crown gall disease of fruits and trees and shrubs.
Professor Abhaya Dandekar and doctoral candidate Matthew Escobar, of the UC Davis pomology department, discovered that gene silencing can be used to interrupt the process of tumor formation in crown gall disease.
Crown gall tumors vary considerably in their morphology, ranging from recognizable stem or root tissue to a chaotic mixture of cell types (Drummond, 1979).
Winston Brill of Agracetus says the proposal describes a model system only; crown gall disease is not normally a problem with tobacco.
He and several collaborators named three new bacterial species that affected plants, and published a paper showing for the first time that crown gall of plants could be cured.
Inspect plants carefully before purchasing to find evidence of invaders such as spider mites, scale insects or mealybugs, or root swellings that might mean crown gall disease on plants such as flowering cherries or roses.
During the first decade of the 20th century, the plant disease crown gall was found to be caused by the soil bacteria later called A.
Crown Gall is a neoplastic plant disease caused by A.
For example, a helpful soil microorganism, Agrobacterium radiobacter, controls crown gall in crops like peach, apple, or rose.