Botany lecture notes

Host Selective and Non-Host Selective Toxins in Host Parasite Interactions and Pathogenesis


toxins in plant pathogen interactions

Toxins in Plant Pathogenesis
Toxins in Plant Pathogen Interaction

The process of pathogenesis (the onset of diseased condition) in plants is facilitated by many factors such as virulence of the pathogen, susceptibility of the host, presence of suitable environmental conditions and various enzymes and metabolites of pathogens. Previously we have discussed the importance of different enzymes involved in plant pathogen interactions. These enzymes facilitate the entry of the pathogen into the host and help to colonize inside the host cell. The production of different hydrolytic enzymes may not always result in the establishment of pathogen inside the host tissue. Certain plant pathogen may successfully invade the host tissue area but fail to induce the onset of disease. These findings highlighted the involvement of certain toxins, microbial toxins or aggressins, in the establishment of diseased conditions in plants. The present post describes the Toxins involved in plant pathogen interaction and pathogenesis with examples.

What is meant by ‘toxin’ in Plant Pathology?

Ø  Definition: Any substances produced by a pathogen which is injurious to host and it directly and immediately play a crucial role in pathogenesis.

Ø  Toxins involved in plant parasite interactions are also called as aggressin.

Ø  According to Koch’s postulates, a substance to be called as a ‘toxin’ should follow the following criterions:

@.   The compound must be isolated from the diseased plant

@.   It should NOT be present in the healthy plant

@.   Compound must be chemically characterized

@.   When isolated toxin is reintroduced to a healthy host, it should produce the original symptoms.

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Botany lecture notes

Enzymes in Plant Pathogenesis (Host Parasite Interactions-Part I)


Host Parasite Interactions

(Plant-Pathogen Interaction Part I: Enzymes in Plant Pathology)


What are the enzymes involved in pathogenesis (plant pathology)?

Most of the fungal and bacterial parasites produce many enzymes that degrade the plant materials in vivo. Enzymes involved in pathogenesis or virulence (process of disease initiation) includes both constitutive and inducible enzymes.

(1). Constitutive enzymes are those enzymes which are present all the time in the cells.

(2). Inducible enzymes are those enzymes which are produced only when they are needed by the cells in response to certain internal or external stimuli.

Important classes of enzymes involved in pathogenesis are:

(1). Cutinases

(2). Pectinases

(3). Cellulases

(4). Hemicellulases

(5). Ligninases

(6). Lipases

(7). Proteinases

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