Cuscuta reflexa is a plant parasite that grows without roots or leaves at the shoots of other plants. With the so called haustoria, the parasite infiltrates the tissue of compatible hosts and scavenges nutrients, assimilates and water. Because of the fact that Cuscuta spec. has a wide host range and attacks many economically important crops, the parasite can cause extensive damage. Studies have shown that for example C. pentagona infestation reduced tomato yield by 50 to 75% in California. Among several lytic enzymes, an herbal cysteineprotease (cuscuin) is expressed in the haustoria during the interaction between a host and the plant parasite. In the present study, cuscuin was expressed in E. coli and isolated. The protease was characterized with FTC-Casein as a substrate in a fluorimeter. Optimal reaction temperature, pH, Ki and the Km values revealed that the protease had many similarities with previously characterized cysteineproteases of other parasitic organisms. The enzyme was found to be stable at neutral or slightly alkaline pH and the temperature optimum was 30 0C. The Ki value showed remarkable inhibition of the protease by its propeptide at neutral pH. Other herbal cysteineproteases were more resistant to the propeptide. Tobacco, which is a compatible host for Cuscuta reflexa, was immunized to some extent against its attack by the application of propeptide. The used peptide was identical to the propeptide of already characterized Cysteineprotease cuscuin. Based on the experimental evidences, cuscuin seems to play a key role in hydrolysing the defence enzymes and/or storage proteins of the host, after the cell wall is destroyed by other lytic enzymes. | English |
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