Plant disease resistance

The plant immune response is a natural defense mechanism of plants, similar to the immune response in animals. Since plants do not have antibody-mediated adaptive immunity, the plant immune response count in full for the innate immune response. The fact that this mapping is also evolutionarily correct, indicates the presence of pathogen - associated molecular patterns in plants and animals.

Plants have no antibodies in contrast to vertebrates. However, they are usually against diseases that can be caused by pathogens such as bacteria, nematodes, fungi or viruses resistant. Various defense mechanisms come here used. Saponins, a group of triterpenes are formed by the plants before infection. They provide protection against fungi by binding to sterols in the plasma membrane and thereby destroy them. Other defensive measures put only one during infection.

Induced defense

Under the induced defense molecules bind from the pathogen ( for example, proteins, sterols, polysaccharide fragments) to a receptor protein in plant plasma membrane. The binding of such elicitor of the receptor is activated and sets two signaling cascades in motion. Firstly, the co-located at the plasma membrane NADPH oxidase is activated so that air oxygen to superoxide is reduced. Superoxide anions are reacted in succession to the hydroxyl radicals and hydrogen peroxide. These three reactive oxygen species initiate radical chain reactions with organic molecules from which lipid peroxidation, enzyme inactivation and degradation of nucleic acids result, which pathogen and infected plant cells are affected. The second initiated by the plant receptor signaling cascade leads to calcium-dependent activation of nitric oxide synthase and thus to the formation of nitric oxide, which together with hydrogen peroxide ( H2O2) can trigger the following plant species and pathogenabhängige defense mechanisms:

Hypersensitive reaction

Under the die hypersensitive reaction cells accelerates from surrounding the site of infection, so that the pathogen with the withdrawal of nutrients no propagation ability is given. The dead cells are macroscopically visible as necrotic lesions. The hypersensitive response is a form of programmed cell death, leading inter alia to increased formation of nucleases and proteases that degrade nucleic acids or proteins by hydrolysis. Many plant species respond to pathogen attack by the synthesis of lignin or callose, representing a physical barrier against pathogen spread. A similar response is a proline-rich by hydrogen peroxide -induced cross-linking the proteins in the cell wall, which leads to their compression. Infecting fungi can be blocked with the synthesis of chitinases, the enzymes hydrolyzing chitin as a constituent of the fungal cell wall. In addition, the expression of glucanases or other fungal enzymes attacking can be increased. The synthesis of antimicrobial phytoalexins has been extensively studied in various plants. These secondary metabolites are different substances such as isoflavones in the case of legumes or sesquiterpenes in the case of the nightshade family. According to a pathogen infection, the plant may have an increased resistance to a range of different pathogens, including in previously infested areas. This systemic acquired resistance based inter alia on the aforementioned hydrolytic enzymes. Salicylic acid is likely to result in this case for the synthesis of a lipid ( or lipid derivative ). The signal molecule is transported in the phloem and causes the resistance in not yet infested plant parts. The methylated form of salicylic acid ( methyl salicylate ) is volatile, so that an increased resistance can also be induced in neighboring plants.