Study on the role of free radical at the infection sites of plant pathogenic Bacteria and on its application for the control of plant diseases.

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First, we have devised the way to detect the formation of free radicals by electron spin resonance. Namely, we could minimize the noise by detecting the absorption at room temperature using the freeze-dried whole plants as the samples. Using this system, we have found that many plants showed common and stable absorption of width 8G at around g = 2,004. As the browning of plants due to cellular damage increased, the absorption became higher. when browning was retarded by dipping the plant tissues in NaCl solution, new absorption pattern which resembles to the one of chelated manganese appeared. The latter absorption was also observed in the process of green tea. In the plant pathogenic bacteria, pectin lyase, a plant tissue-macerating enzyme, was found to be induced by the formation of free radicals in plants. Then, we proceeded to the further analysis of free radicals in the browning process induced by pathogenic bacteria using the culture of tobacco cells. One of the nonpathogenic mutants, which was obtained by random transposition and was deficient in inducing browning, was used as the control. From the analyses of ESR absorption and of chemiluminescence, we could show that the free radicals are involved in the early event of the infection by plant pathogens. These data indicate that plant breeding by single cell selection and disease management can be done by interfering the balance of the formation and destruction of free radicals.