A Novel Burdock Fructooligosaccharide Induces Changes in the Production of Salicylates, Activates Defence Enzymes and Induces Systemic Acquired Resistance to Colletotrichum orbiculare in Cucumber Seedlings

摘要

The ability of burdock fructooligosaccharide (BFO), a type of linear fructooligosaccharide extracted and isolated from the roots of Arctium lappa, to induce systemic acquired resistance (SAR) was studied in cucumber seedlings. BFO strongly induced changes in salicylic acid (SA) and SA-glucoside (SAG) in BFO-treated leaves, and similar changes of SA and SAG were also found in untreated leaves of the same seedling. The level of SA in the first leaves sprayed with BFO (5.0 g/l) increased by 3.6 times after 24 h and then gradually declined from 48 to 96 h and finally decreased to a nadir at 120 h. The SAG level increased by 2.1 times at 24 h and then continued to increase to about 10.0 times as much as that in control from 96 to 120 h. The levels of SA in the untreated leaves of the same seedling only increased by 1.6-1.9 times during the period of 24-72 h followed by a decrease at 120 h, while SAG increased by 1.1 times at 24 h but steadily continued to increase to its maximum from 24 to 120 h. In summary, the patterns of expression of SA and SAG in the untreated leaf were similar to that of the treated leaf of the same seedling, while the pattern of expression of SAG was quite different from that of SA both in the treated and untreated leaves. Pretreatment with BFO reduced the lesions caused by Colletotrichum orbiculare by 56.8%. Additionally, the amount of lignin and the activities of some defensive enzymes including peroxidase, superoxide dismutase, polyphenoloxidase and o-1,3-glucanase significantly increased in the first leaves pretreated with BFO and followed with C. orbiculare inoculation. These results demonstrate that BFO can enhance the contents of endogenous SA, the resistance against C. orbiculare, and the activities of defensive enzymes of cucumber seedlings.