Investigations about the occurrence and chemical nature of the resistance inducing factor in the extract of Reynoutria sachalinensis.
1992
Kowalewski A. | Herger G.
Extracts from the leaves of the giant knotweed, Reynoutria sachalinensis (Polygonaceae) induce a systemic resistance against powdery mildew on cucumbers, tomatoes and several other plants. Plants from different sites were examined for a period of two years for possible differences in their growth rate and efficacy. Growth was better when the site provided high amounts of water and when nitrogen supply was sufficient. Leaf material collected in early spring showed less activity than that collected later in the season. In plants from all sites the amount of the active principle increased in early spring and then remained constant throughout the year. On the basis of these results the conclusion was drawn that the first harvest should be carried out in the middle of June at the earliest. Investigations about the chemical nature of the active constituents excluded the involvement of proteins, terpenoids, phenolic substances and regular sugars. A bulk transfer (ether/water, HCl/NaOH) showed that the constituents were rather polar. After extraction of the water extract with ethylacetate, the active principle was equally distributed in the aqueous and in the organic phase. The active substance had a high affinity for different column matrixes. It was concluded that the resistance inducing factor is most likely a carbohydrate with a hydrophobic part. The inactive sap from squeezed leaves gained activity by boiling it with acid. It seemed that the active principle was formed out of a precursor by acid hydrolysis or during the extraction procedure.
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