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Many anthropogenic activities (smelters, mines and municipal waste) enhance the heavy metal toxicity in soil and water and it is gradually accumulated in plants, and finally through food chain it reaches to human beings. To investigate hazardous impact of excess nickel on growth, biomass, yield and metabolism of rice (Oryza sativa L) the plants were grown in refined sand at 0.0001mM (control), 0.05, 0.10, 0.20, 0.40, and 0.50 mM nickel (Ni) supply. After 16 days of treatment the excess supply of Ni(>0.50mM) reduced biomass, photosynthetic pigments (both chlorophyll a and b), Hill reaction activity, water soluble proteins, activity of catalase (CAT), and enhanced the activity of peroxidase (POX), ribonuclease and acid phosphatase in rice leaves. The antioxidative regulation was inhibited through CAT, although increased activity of POX supported the plants in overcoming the toxic effect of nickel. At 112 days (70 days after Ni treatment) the accumulation of iron in shoot and root was reduced. Phosphorus was significantly increased in both shoot and root. Sulphur accumulation was increased in panicle, leaves, shoot and root. Nickel accumulation in different plant parts was increased many fold (as in leaves it was increased about 25 times, in stem 18 times and in roots it was 17 times) in 0.50 mM Ni supply in comparision to control. Rice appeared very prone to nickel toxicity as Ni supply beyond 0.050 mM resulted into complete loss of economic yield due to inhibited flowering and poor panicle numbers.
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