| Ni is a kind of heavy metal with potential toxicity, a component of urease. It’s the essential trace element, but the excess of Ni will block the growth and development of the crops. Although Ni pollution is less serious than Cd, Hg, Pb and other elements now, however, it’s hard for Ni to migrate in the environment, it is difficult to improve and eliminate once it is polluted. At the same time, the easy migration paticularity of Ni in plants can enhance the harmfulness. Therefore, it is necessary to fully understand the toxicity of Ni on plants and the tolerant mechanism of plant to Ni Stress. In this paper, taking Hydrocarbons dubia B L.Backer and Potamogeton crispus L aseptic, as experimental material, it’s aimed to study the influence of Ni stress on the biochemical parameters of various biology, and thus able to further explore the adaptation strategies taken by plants under the Ni stress. The results are as follows:(1) This author adopts the method of hydroponic nutrient to study the effects of Ni concentrations added in the different experiments (0,0.05,0.10,0.15 and 0.20 mmol/L) on the Ni and nutrient elements contents, oxidative stress and antioxidant system in Hydrocharis dubia leaves. The results indicated that:(a) Ni content in leaves increases with the Ni concentration in solution. (b) Nutrient elements (Ca, Mg, K, Fe, Mn) are also affected with the solution. The content of Ca and Mg increases significantly with the increase of Ni concentration in solution. The content of K increases, but not significantly in leaves. Though Mn content of leaves decreases in the solution with higher Ni concentration, the treatment groups contain generally Mn in leaves higher than the control group. However, Fe content in leaves declines with the increasing of Ni concentration in solution. (c) Ni stress induces the apparent oxidative stress, characteristic of the increases of the productive rate of O2- and the contents of H2O2 and MDA, and the obvious decreases of the contents of soluble protein and photosynthetic pigment in leaves. (d) With the increase of Ni concentration in solution, the activity of peroxidase in leaves increases gradually, while the activity of catalase is declined, followed by the firstly increasing and then decreasing activity of superoxide dismutase at 0.05 mmol/L in leaves. The content of vitamin E and flavonoids in leaves rises slowly with the increasing of Ni concentration in leaves. No apparent change of the glutathione is observed. The content of non-protein thiol and plant complexation both show increases at first. Total antioxidant capacity enhances firstly with Ni concentration in solution. Thus it can be seen that Ni stress causes the accumulation of Ni and the variation of nutrient elements in Hydrocharis dubia leaves, and generates obvious oxidative stress, breaking the balance of antioxidant system.(2) In order to study the potential antioxidant defense mechanisms, adding different concentrations of Ni (0,0.05,0.10,0.15,0.20 mmol/L) to Potamogeton crispus L aseptic, to study the changes in reactive oxygen species (O2- generation rate, H2O2 content), the content of MDA of the product of membrane lipid oxidation, anti-oxidase activities (SOD, POD, CAT, APX, GR), the content of antioxidant (Vc, VE, flavonoids, GSH, PCs) and total antioxidant capacity. The results show that:a, O2-generation rate, H2O2 content and MDA content increase with the increase of Ni concentration. b, anti-oxidase activity shows the increase at first and then decrease with the increase of Ni concentration, the maximum of APX and POD activity appear at Ni concentration of 0.10 mmol/L, the peaks of other four enzyme activities show at Ni concentration of 0.05 mmol/L. c, the content of total flavonoids and PCs rise with the increasing of Ni concentration, VE, GSH and NP-SH content increase at first and then decrease, the content of Vc decreases significantly with the increase of Ni concentration. d, total antioxidant capacity decreased with the increasing of Ni concentrations. Thus it can be seen that Ni addition in P.crispus aseptic causes oxidative stress and the change of antioxidant enzymes activity and the content of antioxidants in plants, and eventually destroys the antioxidant system of plants.(3) Adding different concentrations of Ni (0,0.05,0.10,0.15,0.20 mmol/L) to P.crispus aseptic, to research the influence of Ni stress on the photosynthetic system, root activity and nutrient absorption, amino acid content, soluble protein and soluble sugar contents and FTIR characteristic indexes. The results show:With the Ni concentration increasing, photosynthetic pigment content decreases, chloroplast structure was destroyed; the root activity weakens, Ni element accumulates greatly, the contents of Ca, Mg, Fe, Mn, Cu decrease significantly, but the Zn content increases; the contents of Asp, Ser, Met, Leu and Lys decrease after increasing; and the contents of Glu, His, Gly, Thr, Ala, Arg, Phe, Val, Cys, Tyr and Ile decrease with the increasing of Ni concentration; the peaks of 2930 cm-1,1650 cm-1 and 1410 cm-1 decline with the increasing of Ni concentration, but the peaks of 3350 cm-1 and 1060 cm-1 firstly increase and then decrease; after the first increase, soluble sugar content decreases, while soluble protein content has been on the decline. |
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