Studies On Arsenic Toxicity To Maize And Wheat And Toxicity-Alleviating Effects Of Phosphorus And Sulfur

The experiment was carried out in the Maize Technological Innovation center in the Yellow River Basin and the Huaihe River Basin and in the States Key Laboratory of Crop Biology from 2008 to 2011.This study used the technology line of integration of pot experiment in the field and physiological and biochemical experiments indoor. We studied the effects of arsenic on maize (ZD958) and wheat (JM20) under several concentrations of arsenate. The contents of study included yield, quality, metabolism of carbohydrate and nitrogen, antioxidant system and soil enzymes. The results summaries were as follows:1 Effect of arsenic on yield,grain quality and plant properties in maize and wheatBiomass and grain yield had similar changing rule with arsenic treatments. At the lowest arsenic concentration (A1), it enhanced these yields. When it came to higher concentrations(A2,A3,A4), biomass and yield decreased significantly.When Arsenic concentration reached to 200mg·kg-1, seed germination and seedling growth of maize and wheat had been seriously inhibited and dry matter accumulation was very low, and plant could not flowering , even to death.Arsenic significantly affected grain quality of maize and wheat. The contents of starch, protein and fat firstly increased and then decreased with increased arsenic concentration, and the maximum appeared at A1 treatment. Lower concentration (A1) of arsenic stimulated plant growth of maize and wheat, and plant height and stem diameter increased significantly. While higher concentrations of arsenic stress severely inhibited growth and development of maize and wheat, and plants were short, stems thin, root growth slow, photosynthetic pigment content reduced, and plants grew weaker. Arsenic stress also caused spikes of wheat and the number of effective tillers to reduce. Effect of arsenic on yield of maize lay in kernel number per plant and the impact of wheat mainly determined by effective panicles number per plant.2 Effect of arsenic on metabolism of carbohydrate and nitrogen in maize and wheatDifferent concentrations of arsenic significantly affected metabolism of carbohydrate in maize and wheat, specifically as follows: lower concentration of arsenic (A1) increased photosynthetic pigments content, improved the net photosynthetic rate of plants significantly, promoted the synthesis of soluble sugar and sucrose of plant organs and increased.dry matter accumulation With increasing concentrations of arsenic (A3, A4), arsenic stress inhibited the photosynthetic performance of maize and wheat: photosynthetic pigments content were reduced, leaf area index decreased, the net photosynthetic rate of plants significantly fell.Arsenic significantly affected metabolism of nitrogen in maize and wheat. Lower arsenic concentrations increased free amino acids of different organs, while higher arsenic concentrations destroyed nitrogen metabolism system and nitrogen metabolism disordered. The degree of effect of arsenic on free amino acids in different organs showed stem>leaf>root, and arsenic increased the protein content of corn roots and stems and reduced the protein content of leaves in maize. There were growing stages differences among wheat protein content of each organ, and arsenic had the greatest impact on protein content of wheat stem. The effect of arsenic on nitrogen metabolism enzyme activities was due to crop types, growing stage and plant parts. A1 treatment improved NR, GS and GOGAT activity of maize leaves from jointing to milky, while reduced GS activity of maize leaf at three-leaf stage; highest concentration (A3) of arsenic stress significantly increased root GS activity of maize seedling and reduced NR, GOGAT, GDH activity of leaf and root.3 Effect of arsenic on antioxidant system of maize and wheat3.1 Effect of arsenic on antioxidant system of maizeLeaf SOD activities were positively correlated with Arsenic concentrations at three-leaf stage; with the delay of growth stage ,from flowering to milky, SOD activity first increased and then decreased, and A2 reached the peak of it. CAT activity increased gradually at three-leaf stage of maize. And at jointing stage, root CAT activity first increased and then decreased while leaf CAT activity gradually increased; from flowering to milky, root CAT activity in was the most at A1 treatment, and with the increased of arsenic concentrations it decreased significantly.The effect of arsenic on leaf ascorbic acid (AsA) content was less at three-leaf stage, and AsA content significantly reduced from jointing to milky. Arsenic impeded the synthesis of root ascorbic acid, and limited root AsA-GSH antioxidant system. Leaf GSH content increased at different arsenic levels, and root GSH content was positively correlated with arsenic concentrations at three-leaf stage and anthesis, while root GSH content was negatively correlated with arsenic concentrations at jointing stage and milky, correlation coefficients were 0.99, it indicated that GSH content of maize roots was related to maize growth stages. H₂O₂ content and MDA content in leaves and roots increased with the increased of arsenic concentrations at different growth stages. From three-leaf stage to anthesis, leaf proline content of maize increased with the increased of arsenic concentrations, while root proline content firstly increased and then decreased.3.2 Effect of arsenic on antioxidant system of wheatSOD activity of wheat leaves increased with the increased arsenic concentrations and then decreased. SOD activity of roots decreased at different arsenic concentrations. At A1 and A2 treatment, POD activity in leaves and roots were significantly higher than CK. Arsenic had less effect on AsA content of roots at jointing stage; AsA content significantly increased at A1 and A2 treatments from flowering to milky, and A3 treatment inhibited AsA content. Leaves GSH content gradually increased with increased arsenic levels and leaves GSH content reached to peak at milky.At different growth stages, H₂O₂ content and MDA content of leaves and roots increased with increased arsenic concentrations. From Jointing to mature, proline content of wheat leaf decreased with increased arsenic concentrations, and roots was just the reverse.4 Effect of arsenic on hormone content of maizeArsenic promoted IAA synthesis of maize leaf at three-leaf stage and jointing stage. With the delay of the growth stages, higher concentrations of arsenic stress inhibited IAA synthesis of leaves from anthesis to mature. Maize root IAA content was significantly positively correlated with arsenic concentrations. At three-leaf stage, leaf GA contents were higher than CK. From Jointing to milky stage, leaf GA content firstly increased and then decreased, and the peak appeared at the A1 treatment. At different growth stages of root, GA content which was affected by soil arsenic concentrations was in the order of A3>A2>A1>CK, it indicated that high concentrations of arsenic significantly promoted synthesis of root GA. At three-leaf stage, leaf ZR content at different arsenic treatments were higher than CK, while leaves ZR content firstly increased and then decreased from jointing stage to anthesis, and the maximum appeared at A1 treatment, while it at the milky was significantly lower than CK. The behavior of ZR content in maize roots was basically the same, ZR content of roots firstly increased and then decreased; the maximum appeared at A1 treatment at three-leaf stage. During the other 3 stages, the peaks were atA2 treatment.Under different concentrations of arsenic, maize enhanced the body's resistance to arsenic by increasing the concentrations of ABA, which may be one of the mechanisms of arsenic tolerance in maize.5 Effect of arsenic on soil enzymes activities in maize and wheat5.1 Effect of arsenic on soil enzymes activities in maizeArsenic inhibited soil urease and peroxidase activity. At Jointing and maturity, soil invertase activity increased with the increased arsenic concentrations, while soil invertase activity first increased and then decreased at anthesis, and the maximum in A2 treatment. At jointing stage, soil protease activity increases with the increased concentration of arsenic; and at anthesis and maturity, soil protease activity firstly increased and then decreased, and the maximum was in the A2 and A3 treatment respectively. At different growth stages, soil catalase activity firstly increased and then decreased, the peak appeared in A2 treatment. Alkaline phosphatase was consistent with acid phosphatase activity with the increased arsenic concentration. The tolerance to arsenic of soil neutral phosphatase was higher than acid phosphatase5.2 Effect of arsenic on soil enzymes activities in wheatArsenic also inhibited urease and peroxidase activity in wheat. At jointing stage, soil invertase activity increased with the increased arsenic concentrations, and from anthesis to maturity of wheat, soil invertase activity firstly increased and then decreased, and the maximum appears in the A3 treatment. The same as soil protease activity. Lower concentrations of arsenic increased the phosphatase activity, and higher concentrations of arsenic severely inhibited phosphatase activity. 6 Phosphorus and sulfur had alleviating effects to arsenic poisoning in maize and wheatThe application of phosphorus could reduce toxicity of high arsenic concentrations to maize and wheat: plant biomass and grain yield increased, quality improved,plant arsenic accumulation reduced. While metabolism of carbohydrate and nitrogen made a quick recovery, photosynthetic capacity improved and the plant's tolerance to arsenic enhanced. The application of phosphorus can be used as an effective remediation to arsenic contaminated soil.The application of sulfur has the opposite effect on maize and wheat under arsenic stress: the application of sulfur could reduce toxicity of high arsenic concentrations to maize, while increased the toxicity to wheat, which may be related to the sensitivity of sulfur in wheat and maize.