Effects Of Zn?Fe And Cu Combination Stresses On Seed Germination, Physiological And Biochemical Characteristics In Wheat Seedlings

With the development of industrialization and urbanization of the city continues todeepen, heavy metal contamination almost become a global environmental problem. Heavymetals mostly coexist in soil. The coexistence of heavy metals will change the order ofadsorption of a single heavy metal enter into plants, while the occurrence of various reactionbetween the metal ions and metal ions, between the metal and formation of the soil will alterthe soil physical and chemical intermediates environment, microbial active, activity andmorphology of the metal itself and the presence of the distribution in the soil, therebyaffecting the toxic effects of single heavy metals in plant body. Zinc (Zn), iron (Fe), copper(Cu) as essential micronutrients for plant growth, are cofactor of many enzymes in plants andthey are closely related to photosynthesis, the normal operation of carbohydrates, resistanceand other biological processes. The excessive Zn, Fe and Cu will disrupt normal biologicalmetabolism in plants, including the effect of plant respiration, inhibiting photosynthesis, effectof water metabolism of plants and membrane integrity, it would disrupt the plantscarbohydrate metabolism, reactive oxygen species and ion balance etc.. In the present study,wheat (Triticum aestivum, cv Ningchun4) was used as the experimental material toinvestigate seed germination and physiological characteristics in wheat seedlings afterdifferent combined treatments with Zn, Fe and Cu. The purpose of this study was toinvestigate the response mechanism of plant exposed Zn, Fe and Cu in combination. The keyfindings are as follows:1. Zn, Fe and Cu combined treatments caused significant increase in Zn, Fe and Cu contentsin roots and leaves. Two heavy metal combination treatments did not affect seedgermination, but reduced root length. And also, except for Zn+Fe treatment, the othertwo heavy metal combination treatments inhibited significantly the growth of shoot, butZn+Fe+Cu resulted in a significant reduction in these three parameters.2. All combined treatments also led to significant increases in the levels of malondialdehyde(MDA), hydrogen peroxide (H2O2) and hydroxyl radical (·OH) including apoplastic H2O2and·OH as well as the loss of cell viability and superoxide onion (O2) level in wheatroots, with the highest oxidative damage and the lowest cell viability in Zn+Fe+Cu-treated roots.3. Catalase(CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities increased in roots when exposed to Zn+Fe and Zn+Cu stresses, and that the lowestactivities of soluble peroxidase (POD) and APX was detected in Zn+Fe+Cu treatedroots. Differently, in apoplast the inhibition of SOD and APX but the stimulation of POD,CAT and GR was found under all combined treatments with Zn, Fe and Cu. In addition,compared with the control, various combined treatments stimulated polyamine oxidase(PAO) but inhibited cell wall-bound POD and diamine oxidase (DAO).4. The results show that soluble protein, soluble sugar and proline content increase undervarious heavy metal stresses. The highest content of soluble protein and proline contentwith Zn+Fe+Cu treatment, but the highest content of soluble sugar content with Zn+Cu treatment.5. Root ornithine aminotransferase (OAT) activity in wheat seedlings increases comparedwith the control, but proline dehydrogenase (PDH) activity decreases under various heavymetal stresses. Differently, glutamate kinase (GK) activity has no significant change undersingle heavy metal and Zn+Fe treatments, but the activity of this enzyme increasessignificantly in response to Zn+Cu?Fe+Cu and Zn+Fe+Cu treatments.In conclusion, the results showed that all combined treatments did not obvious affect seedgermination, but significant inhibited the growth of wheat seedling. We can propose that theinhibition of root growth was associated with the increase of lipid peroxidation and the loss ofcell viability under various Zn, Fe and Cu interactions, and that decreased cell wall-boundPOD activity might be responsible for the inhibition of root growth. Antioxidant enzymeactivities are changed in various degrees in wheat seedlings, relieving the damage by theaccmlation of ROS. In addition, Osmotic adjustment content increase in wheat seedling rootsunder various heavy metal stresses. And we can be inferred that the increase of prolinecontent in wheat seedling roots is associated with the changes of OAT, GK and PDH activitiesinduced by Zn, Fe and Cu treatments in combination.