Mechanisms of some Toxins

Mechanisms of some Toxins

Prepared by

Fahd Al-Dhabaan

Ph.D. student

Faculty of Science

King Saud University

Pathotoxin

Pathotoxin is a chemical of biological origin other than an enzyme that plays an important role in a plant disease.

Most pathotoxins are produced by plant pathogenic fungi such as Alternaria alternata or bacteria such as Pseudomonas seruginosa, but some are produced by higher plants, and one has been reported to be the product of an interaction between a plant and a bacterial pathogen.

Properties of Pathotoxins

1.Some pathotoxins are selective in their action but others are nonselective.

2.Some of pathotoxins act as plant growth regulators.

3.Pathotoxins are considered microtoxins due to small size of their molecules.

4.Pathotoxins cause plant diseases as well as fungal-fungal destruction.

Chemistry and mode of action of pathotoxins

Pathotoxins mean toxins which cause pathogenicity to organisms. Pathotoxins group included various members of toxins each of which has specific manner such as gibberellins, fusicoccin, and tentoxin.

Gibberellins

   The gibberellins were produced by the fungus Gibberella fujikuroi and cause disease of rice. This fungus which produces gibberellins infects the plant and form long internodes, which typify the effects of this group of plant hormones.

Fusicoccin

   Fusicoccin produced by the fungus Fusicoccum amygdali, which causes a wilt disease of peach and almond trees, is another nonselective pathotoxin with growth-regulator properties.

This chemical also causes stomata to open.

Tentoxin

   Tentoxin is a product of Alternaria alternata, it causes a striking variegated chlorosis in cucumber, cotton, lettuce, and many other sensitive plants, but has no effect on tobacco, radish, willow, or other insensitive species. Tentoxin binds specifically to coupling factor 1 in chloroplasts of sensitive species, and presumably acts by disrupting energy generation in the photophosphorylative electron transport system.

Figure
Leaf spots and chlorosis caused by the Alternaria alternata toxin

Victorin (HV-toxin)

Victorin is produced by the fungus Cochliobolus (Helminthosporium) victoriae. Cochliobolus victoriae infects the basal portions of susceptible oat plants and produces a toxin that is carried to the leaves, causes a leaf blight, and destroys the entire plant. Toxin production in the fungus is controlled by a single gene (Vb).

Victorin cause loss of electrolytes from cells and increased respiration. Subsequently leads to decreased both of growth and protein synthesis.

The toxin not only produces all the external symptoms of the disease induced by the pathogen, but it also produces similar histochemical and biochemical changes in the host, such as changes in cell wall structure

Victorin has been purified and its chemical structure has been determined to be a complex chlorinated, partially cyclic pentapeptide.

The primary target of the toxin seems to be the cell plasma membrane where victorin seems to bind to several proteins. The possible site of action of victorin seems to be the glycine decar-boxylate complex.

Fusaric acid

Fusaric acid is a picolinic acid derivative produced from various Fusarium species such as Fusarium oxysporum, and has been proposed for a various therapeutic applications. However, it is primarily used as a research tool.

Its mechanism of action is not well understood. It likely inhibits Dopamine beta-hydroxylase (the enzyme that converts dopamine to norepinephrine). It may also have other actions, such as the inhibition of cell proliferation and DNA synthesis.

Factors affecting the toxicity

1.Toxin dose: Toxicity depends on the dose of the poison introduced into the host, so that the proportional relationship between the dose of poison and toxicity. The more toxic dose increased the effect of toxicity.

2.Time of poison abuse: Toxicity increases over time from the beginning of the poison abuse where the toxin spreads and dips in the body of the host and be able to cause damage or death.

3. Age of host: Age of host is a significant factor which depend upon it the extent of toxicity. High toxicity be on two phases of the life on opposite sides either in the early or later stages of age due to weakened immunity and little or no resistance to the poison. Youth is the stage of power that can be faced the toxicity correlated with other factors.

4. Nutrition of host: The host can resists the influence of the poison and slows down its spreading if there is proper nutrition because vitamins and proteins delay the activity of the toxin. And vice versa, toxicity increases if the host body was weak due to malnutrition.