It is responsible for swellings known as crown galls.
Plants, as happens in animals, have hormones that perform certain physiological functions, among which are defensive tasks and growth and development. Thus, for example, cytokines act as promoters of the lateral shoot buds of the stem and as repressors of root growth, while auxins produce the opposite effect. The action of both hormones configures the definitive architecture of a plant.
In certain situations, the hormonal balance is broken and excessive growth occurs, which ends up giving rise to the appearance of galls or tumors. The origin of this process must be sought in an uncontrolled cell division generated by the action of certain gill organisms (viruses, bacteria, fungi, mites, insects, or nematodes).
From enemy to ally
Among the bacteria capable of producing galls is Agrobacterium tumefaciens, a gram-negative, flagellated bacillus that inhabits soils. It penetrates the plant through wounds caused during maintenance work or by the action of certain insects and nematodes.
When the bacterium infects a host plant cell, a very high secretion of cytokines and auxins is produced, whose final derivative is uncontrolled cell growth and division, which ends up giving rise to a newly formed tissue, of very diverse shapes and colors.
This disease currently affects more than eighty different families of herbaceous and forest plants. Initially, the galls are woody and maintain both the color and the texture of the bark, but over time they become fragmented and take on a darker color.
Additionally, the bacterium makes the plant work for it, since part of its genetic material interacts with the plant’s genome, causing it to synthesize ‘opens’, amino acids that serve as a source of nitrogen and carbon for the bacterium.
In recent years this singularity of the Agrobacterium has been used for our own benefit, through biotechnology certain plants have been genetically modified so that they are capable of producing the Bt insecticide, a biological alternative to pesticides.
Galls in crown
Tumors caused by these phytopathogenic bacteria can appear both in the root, in the neck, and in the aerial part since the microorganism moves systemically. Those that appear on the neck are larger and usually do so grouped in the form of chains.
The disease usually manifests itself initially as small bulges located at the junction between the roots and the graft, close to the ground, a malformation known as ‘crown galls’.
Fortunately for plants, and unlike what happens in animals, tumors almost never kill them, so they could be considered a protective response against the attack of certain organisms. However, there are situations in which they have negative effects, such as when they affect the leaves since they undermine the process of photosynthesis.