Effects Of H₂O₂Pretreatment On Cd Tolerance Of Diffenent Rice Cultivars

In this thesis, two rice cultivars (N07-6and N07-63) with different Cd tolerance were selected to study the effect of H2O2pretreatment on Cd tolerance and translocation within the seedlings. Variations of the contents of MDA, reduced glutathione (GSH), non-protein thiols (NPT), phytochelatins(PCs) and the activity of glutathione S-transferase (GST) in the two cultivars were compared among the different treatments. Crude ectracts of roots from N07-6under different treatments were separated and analyzed using proteomic methods. The main results are as follows:1. Enhancement of physiological properties by H2O2pretreatment and difference between rice cultivars50μM Cd exposure significantly inhibited the rice growth, reduced plant height, root length, dry weights of shoots and roots, and increased MDA contents (enhancing lipid peroxidation). There was a significant difference between cultivars. N07-6showed greater decline than N07-63in the biomass, and the MDA level in the former cultivar was higher. Compared to Cd-stressed only, addition of H2O2increased the biomass of rice, and N07-63growed better than N07-6, by reducing MDA in N07-63to the level of CK. The H2O2pretreatment alone had no significant effects on rice except that the shoot height was reduced.After Cd exposure, compared with N07-6, N07-63accumulated more Cd in the roots, but Cd in shoots and Cd translocation ratio were lower than that of N07-6. The H2O2pretreatment enhanced Cd uptake in roots of N07-63, but Cd in shoots and roots of N07-6were reduced. Meanwhile, S/R ratios of two cultivars declined, and there was a significant difference between the two cultivars. N07-63had a clearly lower Cd translocation.Cadmium induced productions of NPT, GSH, PCs and enhanced GST activities in the two cultivars. The increases of-SH amount and GST activity in the root of N07-63were significantly higher than those of N07-6. The pretreatment of H2O2further increased the contents of GSH, NPT and PCs and the GST activities in rice root. N07-63had larger increases for those parameters, suggesting its Cd tolerance was enhanced further.The above-mentioned results demonstrated that the Cd tolerance enhancement following H2O2pretreatment was different between the two cultivars. For the N07-63, the Cd toxicity alleviation by H2O2pretreatment was more obvious. This may be related to the higher amount of-SH containing compounds (GSH, NPT, PCs) and higher activities of detoxification enzyme GST, as well as lower Cd translocation in the root of the tolerant rice cultivar.2. Increase of tolerant protein expression by H2O2pretreatment in rice rootsProteins in crude extracts of roots from N07-6were seprated by SDS-PAGE, and the protein bands were cut out for in gel digestions. The resulting peptides were evaluated by MALDI-TOF mass spectrometry. Through the comparison with protein database (Swiss Prot56.7), we identified three proteins:Glutathione reductase(GR), Nucleoside diphosphate kinase(NDPK), Thioredoxin(Trx). They are important proteins for cell redox state and normal metabolism, which can reduce injury caused by Cd. We presumed that H2O2improved Cd tolerance by boosting expression of correlated proteins.