A Prelimnary Study On Mechanism Of Sunflower Resistance To Rust Induced By Oligosaccharide

Sunflower rust, which is one of the major diseases of sunflower, is increasingly serious. A good way to prevention and control of plant diseases is to use the elicitor to induce activation of defense responses of plants. Oligosaccharide elicitor can be used as early signal molecule to activate the plant defense system, In this study, sunflower seedlings treated with oligosaccharide. The effect of oligosaccharide of different concentrations on the disease development, on activity of defensive enzymes in sunflower, on pathogenesis-related protein and cell wall substances in sunflower leaves, on changes of reactive oxygen of sunflower were tested, and ultrastructure of sunflower resistance to rust induced by oligosaccharide was observed to unravel the mechanism of induced resistance to Puccinia hanlianthi. The experimental results showed that:1. The 50, 100, 300, 500, 800-fold dilution oligosaccharide enhance disease resistance for sunflower rust all, the effect of 100-fold dilution is best.2. The leaves of sunflower seedling were induced by different concentrations of oligosaccharide. Four kinds of denfensive enzyme in sunflower leaves were measured. The result of the experiments showed the activity of phenylalanine ammonia-lyase (PAL), polyphenoloxidase (PPO), peroxidase (POD) and catalase (CAT) of sunflower all increased under different treatment.3. After treatment with oligosaccharide,β-1, 3-glucanase and chitinase activities increased, the content of lignin and hydroxyproline-rich glycoprotein (HRGP) enhanced. In another experiment sunflower leaves treated with oligosaccharide and inoculated with Puccinia helianthi Schw. were assayed,β-1,3-glucanase, chitinase and cell wall substances were induced, their production were higher than in other treatments. The results showed that the increase levels of these two enzyme and cell wall substances in sunflower leaves treated with oligosaccharide play an important role in the induced resistance to sunflower =rust.4. Spraying sunflower leaves with oligosaccharide, the production rate of superoxide anions(O2-·) and hydrogen peroxides (H2O2) content of leaves were detected after induction at different time, also reactive oxygen in situ was tested. Results showed that in a period of time after the induction of oligosaccharide, the production rate of O2-·and H2O2 content increased obviously. O2-·reached its peak at 3 hours, H2O2 stayed at a higher level at 3 to 6 hours. In-situ staining reaction also showed that O2--·and H2O2 accumulated significantly at 3 to 6 hours, showing that oligosaccharide induction can lead to an early reactive oxygen accumulation of sunflower plant.5. After treatment with oligosaccharide, some uredospores on the induced plant were sunken and the germination was inhibited. The host cells of sunflower produced defense structures and material related to the infection. The host cell wall was thickened and deeply stained, dark material deposited under the cell wall and the walls of haustoria thickened and extra-haustorial matrix was found to be enlarged; some haustoria became malformed and disintegrated, deformation and vacuolation of host organelles occurred, finally the whole host cell disintegrated, collapsed.