Study On Synthesis Of Oligosaccharide Elicitors And Their Bioactivity To Induce Tobacco Resistance To Phytophthora Nicotianae

It has become evident in recent years that the oligosaccharides as elicitors with particular structures can induce defense response in plants to diseases. To understand structure-biofunction relationship of oligosaccharide elicitors is the key point of the research on glycobiology. The oligosaccharide elicitors from natural sources are not suitable for the research due to their complicated structures and varied molecular weight as well as the difficulty to gain pure preparation from natural products. The chemosynthesis method may obtain the pure oligosaccahrides with explicit structures that are desirable for the research on the structure-biofunction relationship of oligosaccharide elicitors.In the present work, five oligosaccharides were synthesized and their activity as the elicitors to induce tobacco plant resistance to Phytophthora nicotianae was observed.The results are as follows: l.Oligosaccharide elicitors synthesisUsing glucose, lactose, fucose, glucosamine, galactose as the raw material five kinds of oligosaccharide were synthesized with good yields by the ideal schemes. Among them two kinds of Lewis3 oligosaccharides are reported for the first time. All the synthesized compounds are affirmed by mass spectra, NMR and elemental analysis. 1.1 Synthesis of Lewis1 trisaccharide(I) CH2C12- NIS, TfOH, M.S, -10℃, 78%; (II) THF, NaCNBH3, HC1, Et2O, M.S, RT, 92%; (III) AgOTf, Toluene -20℃, 82%; (IV) a. NH2-NH2, H2O, EtOH, b. AC2O, pyridine; c. MeOH, MeONa, 68%; (V) H2, Pd/C,MeOH, 95%(I)AgOTf, DCM,MS, -10, 1.5h,89%; (II)NIS/TOH, Ttoluene, MS, 10min, 65%; (III) CH2C12, NIS/TfOH, MS, -30, 2.5h, 86%; (IV)a. NH2-NH2, H2O, EtOH, 80 refluence b. Ac2O PYRIDINE; c. MeOH, MeONa, 81%; (V) H2 Pd/C,MeOH, 98%(I)NIS/TfOH,DCM, MS,-30, 30m, 73%; (II)MeONa/MeOH, DCM/MeOH l/l,2h,69%; (III) dimethoxytoluene, CH3CN, APTS, RT, 10min, 71%; (IV) NIS/TfOH, DCM,MS, -45, 1 h, 78%; (V) H2NNH2-H2O, ethanol, H2O ,RT, 2 d; (VI) Ac2O, CH2Cl2-MeOH, RT, 24h, 70%; (VII) H2, Pd/C (10%), MeOH, 93%(I) CH2CL2, TMSOTf, MS, -0, 2.5h, 45.7%; (II) CH2C12, triethylsilane, CF3COOH, MS, -0, 85%; (III)Toluene, NIS/TfOHH,MS, RT, 82.5%; (IV) NH2-NH2, H2O, EtOH, 80 refluence; (V)CH2C12, MeOH, Ac2O,RT 12h; (VI) H2, Pd/C,MeOH, 67% (three steps).2. Induced resistance of Tobacco to Phytophthora parasitica by synthesized oligosaccharide elicitorsThe chemically synthesized oligosaccharides induced tobacco resistance against Phytophthora parasitica, although they did not inhibit the mycelial growth of the pathogen in vitro . The induced resistance of tobacco plants treated with Lewisx quinquesaccharide or heptasaccharide was corresponding to the concentration used in the range from 0.01g/mL to 10g/mL, the treated plants showed the maxium disease control efficiency (97.9 %) at 10g/mL. The enzyme activities of the three defense enzymes, Polyphenoloxidase(PPO), Peroxidase(PO) and Phenylalanineammoniayase(PAL) in the tobacco plants treated with Lewis heptasaccharide at 10g/mL were increased with 70.7% 150.0% and 142.8%, respectively. The mechanism of the induced resistance is also discussed.