Tolerance Of Transgenic Rice Overexpressing A Barley Peroxisomal Ascorbate Peroxidase Gene To Cadmium And Zinc Stress

With the development of modern industry, heavy metal concentrations in soils have increased unusually. Phytoremediation approach using hyperaccumulator plants, may offer a valuable solution to this problem, and the approach is gaining more attention. But some hyperaccumulators used to remedy the contaminated environment are not ideal for phytoremediation, since they grow slowly and have a low biomass production. These shortcomings limit their practical application. Improving plants tolerance to heavy metals by genetic engineering, i.e. by modifying processes like heavy metal uptake, transport and accumulation opens up new possibilities for phytoremediation. Experiments were conducted to study the effect of overexpressing peroxisomal type ascorbate peroxidase in rice on enhanced tolerance to cadmium and zinc stress. In addition, the mechanism of tolerance to the heavy metals is also studied in this research. The results can offer scientific basis to raise phytoremediation efficiency. The results summarized are as follows: 1. Identification of HvAPX1 in transgenic plants of T2 generation by PCR. The result indicates that the transgenic plants contain the genetic fragment of HvAPX1, but the wide type plants do not have this genetic fragment. Confirmation of transgene HvAPX1 transcript level in the transgenic plants by RT-PCR technology, the result shows that HvAPX1 gene is overexpressed in T3 generation. 2. The results indicated that with the increase of HvAPX1-transcript in transgenic rice, the total APX activity of transgenic plants of both lines kept at high level while the activity decreased obviously in wide type plants. APX activities of HvAPX1-transgenic plants differ significantly from WT after Cd20μM treatment for 6 days. The elongation rate of main root, the total fresh weight and the leaf chlorophyll content are all significantly higher than that of wild type. The Cd content in both root and shoot of transgenic lines show no significantly difference from WT, but the transgenic plants can accumulate more cadmium compared with the wide-type plants. 3. Adding excessive zinc on transgenic and wide type rice showed that with the overexpressing of the pAPX, the elongation rate of the main root, the total fresh weight, the leaf chlorophyll content and the activity of the APX are all higher obviously than that of wild type. The transgenic plants were significantly more tolerant to zinc stress as compared with the wide-type plants. Different from cadmium stress, transgenic plant can not accumulate more zinc.