| Heavy metal pollution is one of the major environmental problems to the present world because of toxicity of metals to plants when accumulated in food plants and potential risk for human health by food chain. Iron(Fe) is an essential element for plants and plays important roles in such plant biological processes as photosynthetic and respiratory electron transport chains, cell wall metabolism and oxidative stress protection. However, Fe at high levels is toxic, which can cause alterations in the morphologic, biochemical and physiological characteristics of the plants, generate oxidative stress and even inhibit early seedling growth of plants. Zinc(Zn) is not only a key element related to the growth and development of plants, but also has a stabilizing and protective effects on the biomembrane against oxidative and peroxidative damage, and maintains the permeability of the membrane and the integrity of plasma membrane. Moreover, the alleviated effects of Zn on metals-induced oxidative stresses are investigated in some plant species. Differently, Zn at high concentrations is also toxic to plants. Wheat(Tritium aestivum L.) is one of the most important crops in China and many other countries in the world. In the present study, wheat(cv Xihan 3) was used as experimental material to investigate the effects of different Zn concentrations(50 μmol · L-1, 250 μmol · L-1 and 2 mmol · L-1) on the growth of wheat seedlings and physiological characteristics after treatment with 300 μmol · L-1 Fe, trying to explore the response mechanism of plant exposed to Fe after Zn applied. The main results were as follows:1. Compared with the control, significant increases of both Zn content in roots and leaves and the contents of Fe, Potassium(K),Sodium(Na) and Calcium(Ca) in roots were observed in Fe-treated wheat seedlings, while the accumulations of K, Na and Ca obviously elevated in leaves and there was no obvious change of leaf Fe content. Compared with Fe stress, Zn applied resulted in the prominent enhancements of seedling Zn and leaf Ca accumulations as well as the reduction of seedling Fe content in Fe-stressed wheats; the applications of Zn at low levels(50 and 250 μmol · L-1) remarkably lowered root K accumulation; 50 μmol · L-1and 2 mmol · L-1 Zn applied obviously increased leaf K content but decreased the accumulations of root Ca and seedling Na in Fe-treated seedlings.2. Fe treatment remarkably inhibited root growth but did not significantly affect stem growth in comparison with the control. Moreover,the addition of zinc at low levels obviously elevated root length but have no effect on stem growth compared with Fe stress; the application of 2 mmol · L-1 Zn further inhibited the growth of root and stem in Fe-treated seedlings, while the inhibitory effect of 2 mmol · L-1 Zn on roots is stronger.3. Fe stress induced notable enhancements in the malondialdehyde(MDA) content and the loss of cell viability, and the levels of total hydrogen peroxide(H2O2), hydroxyl radical(·OH) and superoxide onion(O2·-) as well as these three paramrters in the apoplast significantly elevated in wheat roots. Compared with Fe treatment, Zn applied obviously reduced the loss of cell viability, and the generations of total O2·- as well as apoplastic H2O2, ·OH and O2·-; zinc at low levels notably decreased the contents of MDA and total H2O2; 50 μmol · L-1 and 2 mmol · L-1 Zn led to insignificant elevation of total ·OH content in roots.4. The activities of total superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), ascorbate peroxidase(APX) and glutathione reductase(GR) significantly elevated in Fe-stressed wheat roots compared with the control; apoplastic GR activity in roots was much lower than the control except the other enzyme activities. The obvious stimulations of total SOD, POD and GR as well as CAT, APX and GR in the apoplast were detected in Fe + Zn-treated roots, while the activities of total APX and apoplastic POD notably reduced; 50 μmol · L-1 and 2 mmol · L-1 Zn significantly lowered apoplastic SOD activity in roots in response to Fe stress; the additions of 250 μmol · L-1 and 2 mmol · L-1 Zn notably stimulated total CAT in roots due to Fe treatment.5. The prominent stimulations of diamine oxidase(DAO) and polyamine oxidase(PAO) as well as the inhibition of cell wall-bound POD were observed in wheat roots exposed to Fe stress. Compared with Fe stress, Zn applied obviously stimulated cell wall-bound POD in roots; Zn at low concentrations led to the reduction of root PAO activity; 50 μmol · L-1 and 2 mmol · L-1 Zn significantly elevated DAO activity in roots.6. Fe treatment remarkably enhanced the contents of soluble protein and proline as well as ornithine δ-aminotransferase(OAT) activity, but reduced soluble sugar content as well as the activities of glutamate kinase(GK) and proline dehydrogenase(PDH) in wheat roots. Compared with Fe treatment, Zn at low levels obviously decreased proline content and the activities of OAT and GK, while increased soluble protein content and PDH activity in roots; the addition of Zn did not notably affect root soluble sugar content.In conclusion, these results suggested that: the addition of Zn at low levels alleviated the phytotoxicity involved in root growth induced by Fe treatment, which may be correlated with the decrease of lipid peroxidation, the decrease of the loss of cell viability, the reduction of ROS accumulation, the stimulations of both total SOD, POD, GR and CAT, APX, GR in the apoplast, the inhibition of PAO, the elevation of soluble protein content as well as the reduction of proline accumulation in wheat roots. However, synergetic effect of Zn at high levels and Fe further enhanced the phytotoxicity involved in wheat roots. |
PDF Full Text Request