Some Aspects Of Chito-Oligosaccharides Induced Resistance In Tobacco To TMV

Chito-oligosaccharide is a linear polymer, in which 2-10 D-glncosamine residues are connected byβ-1, 4 linkages. It was demonstrated that the systemic acquired resistance (SAR) was induced by chito-oligosaccharides. In treated tobacco leaves, systemic symptoms of TMV (tobacco mosaic virus) infection were strongly reduced. The trail was to carry out that the effects of chito-oligosaccarides treatment on H2O2 and PAL, and replication of TMV-MP gene in TMV infected tobacco. The main results were as follows.1. Chito-oligosaccarides treatment induced evident changes in active oxygen. The contents of H2O2 were higher than that of untreated tobacco leaves and had two peaks in tobacco leaves treated with chito-oligosaccharides (50μg/ml). The peaks appeared at 6 h (0.25d) an 11d after inoculated with TMV, respectively their highest point were 169.09%, 128.97% of that untreated leaves.2. PAL activity in treated tobacco leaves showed 2 peaks, respectively at 6h (0.25d) and 1d after inoculated with TMV. The increase was higher than that of untreated leaves. The activity at the two peaks was increased by 90.84% and 46.76% respectively.3. The changes of H2O2 and PAL in treated leaves were used to evaluate the expression features of SAR induced by chito-oligosaccharides, including the effective concentration of chito-oligosaccharide solution, SAR induction phase, its persistence and the effectiveness of chito-oligosaccharide treatment after virus infection.4. The best concentration of chito-oligosaccharides treatment was 50μg/ml, which caused that H2O2 increased by 95.44%, and systemic symptoms of TMV strongly reduced, the same results were obtained in the experiments with PAL activity.5. The H2O2 changes triggered as rapidly as 12h (0.5d) in leaves treated by chito-oligosaccharide. This indicated that induction phase was 12h that short on 1d that revealed of systemic symptoms of TMV infection. The induction phase revealed of PAL activities was as same as that revealed of systemic symptoms of TMV infection. The PAL activity increased by 34.44% at 1d than that of untreated tobacco leaves.6. The H2O2 content and PAL activity were still keep high levels in 9d after treatment, which were 100% and 31.98% higher than untreated leaves respectively. This meant that the effectiveness of resistance lasted more than 9d.7. Chito-oligosaccharide treatments still triggered significant increase of H2O2 content and PAL activity, and lowered the descrease rate of average ID when treated as late as at 5d after challenge inoculation. This meant Chito-oligosaccharide treatment might have inducing effect after TMV infection.8. TMV-MP expression was assayed by real-time quantitative RT-PCR (QRT-PCR) at mRNA level in leaves treated with chito-oligosaccharides (50μg/ml) for 1d. The result showed that replication of TMV-MP gene was reduced by 140.13 times of that in untreated leaves. This date revealed that the replication of TMV-MP gene was significant reduced. The results of experiments showed that the SAR induced by chito-oligosaccharides trigged evident increase of H2O2 content and PAL activity, and distance movement of virus was inhibited by chito-oligosaccharides.The results of experiments also revealed the best concentration of chito-oligosaccharide, the induction phase and persistence of SAR and its effectiveness after TMV infection, which were important basic information to understanding the nature of chito-oligosaccharide induction, and to improved field application technique of chito-oligosaccharide products.