Effects Of Meteothionein Of Elsholtzia Haichowensis On Copper Tolerance In Tobacco

Metallothioneins (MTs) are prevalent in plants. It is involved in many physiological processes, such as growth and development, embryogenesis, senescence, fruit development and maturity, resilience and so on. It implied that MTs may play an important role in these physiological processes. The high-SH group content and the capacity of binding heavy metal determines the diversity of its functions. The feature of MTs that heavy metal stress-induced determines it may play an important role in heavy metal detoxification, anti-oxidation and the plasma membrane repair and it received extensive attention in recent years. The research about impact of heavy metals on MTs gene expression mostly from the point of view that the-SH group of MTs can chelate the heavy metals, however, little research on the point of view that MTs can scavenge of reactive oxygen species. In this paper, to further description the function of MTs, transgenic tobacco plants over-express EhMTl compared with wild-type tobacco to study the different features of combined metal ions, scavenging reactive oxygen systems (ROS) of two genotypes tobacco plants.We first studied the changes on root elongation, the biomass, contents of Cu, Zn, Mn and Fe in the wild-type and the transgenic tobacco. The subcellular distribution of Cu, Zn, Mn and Fe of two genotype tobaccos were discussed. Try to explain the role of MTs in the process of Cu tolerance through the differences of two genotypes. The results showed that the root elongation of the transgenic type is logger than the wild-type, what is more, the biomass of transgenic type is also higher than the wild-type. It shows that the transgenic type is more tolerant to Cu than the wild-type. The absorption of Cu, Zn, Mn and Fe of transgenic type is also stronger than the wild-type. We also found that the transgenic type tend to turn the excess Cu, Zn, Mn mainly stored in the cytoplasm, while the wild-type turn the excess Cu, Zn, Mn mainly stored in the cell wall. This may be related to the transgenic type have more expression of MT in the cytoplasm, which combines the more metal.Excess Cu can cause an increased formation of ROS. However, plants have evolved antioxidative defence systems to keep ROS under the control. Under the Cu stress, the activity of antioxidant enzymes and the contents of non-enzymatic antioxidants were determined in two genotypes of tobacco. Focused on determination the changes in the content of H2O2and O2-before and after copper treatment. Try to explain the role of EhMTl in the process of antioxidant through the differences of two genotypes in the anti-oxidation system. We also observed the deposition of H2O2and O2-of two genotypes by utilize the transmission electron microscopy. The result showed that the H2O2and O2-levels of transgenic tobacco were lower than the wild type after Cu treatment. The time curve charts of the levels of H2O2and O2-of two genotypes were showed that the content of H2O2in transgenic type reached the maximum when dealing with36hours while the content of H2O2in wild type reached the maximum when dealing with12hours. We speculate that is due to the reduction of Cu stress concentration because of the MTs can chelate the Cu which is in free. In this way, it reduced the harm of plants and delayed the emergence of the peak time of H2O2. The O2-levels of transgenic tobacco was significantly decreased when Cu treatment for12-24hours. This may be related to the SOD activities reached peak after24hours treatment in transgenic type. The results from the electron microscope showed that the deposition of H2O2and O2-in transgenic tobacco were less than wild-type, which is consistent with the previous experimental results of us.