| Plant disease caused by virus endangered the agriculture badly. Tobacco mosaic virus, one of the primary plant viruses made severe menace to the yield and quality of crops. It was vital content of plant defence to find an efficient measure to prevent the Tobacco mosaic virus. The resistant abilities in plant could be induced by some kinds of elicitors. In this paper alginate oligosaccharide and fucoidan oligosaccharide were prepared and their abilities of eliciting the defence reaction were studied.Alginate and fucoidan were exacted in boiling water from brown alga (Laminarin japonicd), and were purified by ethanol and DEAE-Cellulose ion-exchange chromatography.Alginate was partial hydrolyzed with 0.25N HC1 and 90% formate at 90℃ , snai 1 enzyme at 25℃ (pH=8. 5) respectively. The fucoidan was also treated by 0. 25N HC1 at 90℃. The products were isolated and deposited by 80% and 98% ethanol. The results showed that the percentages of alginate oligosaccharide output were 0.53%, 11.3%, 9.7%, respectively,. When the hydrolysis maintained about 8 hours. However the percentage of fucoidan oligosaccharide output reachs about 75% with the hydrolysis by HC1 about 4 hours, and the yield decreases after 4 hours. The alginate oligosaccharide with average degree of polymerization 8-20 and fucoidan oligosaccharide with average degree of polymerization 6-20 were further separated through sephdex G-25 gel filtration.The next study tested and compared with the activities between alginate and fucoidan oligosaccharides to elicit phenylalanine ammonia-lyase (PAL) and peroxidase (POD) when the oligosaccharides treated the tobacco leaves. The results indicated that both of the oligosaccharides acted as elicitors on eliciting the activities of POD and PAL. The activity of POD increased after 4 days when it was treated withalginate oligosaccharide, and it is the 6 days that the activity of POD attained the highest level. The fucoidan oligosaccharide elicits the POD activity after 2 days and reached the highest level on the 6th day. The activity of PAL increased after 2 days when it was treated with alginate oligosaccharide, it was on the 5 day that the activity of PAL attained the highest level. The fucoidan oligosaccharide elicits the PAL activity after 2 days and reached the highest level on the 4th day.The effect of the two oligosaccharides on the tobacco defence enzyme activity with different concentration (600μg ml-1, 800μg ml-1, 1000μg ml-1,1 200μg ml-1) was also studied. The results showed that the activities of POD and PAL increased with the concentration of the two oligosaccharides changed from 600μg .v.ml-1 to 1000μg ml-1 and the highest enzyme activity was showed when the concentration at 1 000μg ml-1, Moreover, it doesn't exist significant difference beyond the concentration of 1 000μgml-1,.The effect of the two brown alga oligosaccharides on tobacco anti- Tobacco mosaic virus activity was investgated, the data showed that both the oligosaccharides can elicit the anti- Tobacco mosaic virus activity of tobacco, It was found that the anti-Tobacco mosaic virus activity is observed after 4 days, the highest anti- Tobacco mosaic virus activity elicited by alginate oligosaccharide was obtained in 6 days, and fucoidan oligosaccharide after 8 days.The resistance induced by the brown alga oligosaccharides was studied with the concentration of 600μg ml-1, 800μg ml-1, 1 000μg.ml-1, 1200μg ml-1, 1400μg ml-1 respectively., and the highest activity of tobacco to against Tobacco mosaic virus was observed with the concentration of 1 000μg ml-1, and the highest rate of resistance to Tobacco mosaic virus in tobacco achieved about 60%.The results indicate that alginate oligosaccharide and fucoidan oligosaccharide are two powerful elicitors to induce the defence reaction in plant, and they were possibly used as non-pollution new pesticides. |
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