A pathotoxin is a naturally occurring poison, produced by living organisms, that directly causes plant disease. It's a chemical, not an enzyme, that disrupts the plant's metabolism leading to illness. Most pathotoxins are created by plant pathogenic fungi or bacteria, but some originate from higher plants themselves. In some cases, a pathotoxin can even be a product of a plant and bacterium interaction.
Understanding Pathotoxins
- Source: Primarily produced by plant pathogenic fungi and bacteria. Examples include Helminthosporium maydis race T, producing the T-toxin, and Xanthomonas albilineans, producing albicidin.
- Mechanism: Pathotoxins disrupt the host plant's cellular metabolism. The T-toxin, for instance, inhibits oxidation of α-ketoglutarate and malate while stimulating NADH oxidation in susceptible maize plants.
- Specificity: Some pathotoxins are host-selective, meaning they only affect certain plant species or varieties. This characteristic makes them crucial in understanding disease resistance mechanisms.
- Impact: They are a major factor in various plant diseases, causing significant damage to crops.
Examples of Pathotoxins and Their Effects
- T-toxin (from Helminthosporium maydis race T): Causes Southern corn leaf blight, affecting maize plants with Texas male-sterile cytoplasm (cms-T). Non-sterile cytoplasm maize is resistant.
- Albicidin (from Xanthomonas albilineans): Causes leaf scald disease in sugarcane.
Distinguishing Pathotoxins from Other Toxins
While all pathotoxins are toxins (naturally occurring poisons produced by living organisms), not all toxins are pathotoxins. A toxin could be produced by an animal or a bacterium that doesn't specifically cause plant disease. Pathotoxins are specifically defined by their causal role in plant pathology.
