Abstract
Nickel (Ni) is an essential micronutrient for plants but in high concentrations may turn toxic. This paper discusses the potential role of humic acid (HA) and sodium nitroprusside in modulating or preventing oxidative stress in rice plants. Three genes [superoxide dismutase (SOD) glutathione reductase (GR) and ascorbate peroxidase (APx) were selected for an expression study using a real time PCR technique. Three different treatments (T1 = nickel [nickel chloride (NiCl2·6H2O)] 300 mg L-1, T2 = nickel-humic acid, T3 = nickel-sodium nitroprusside) were used to determine the effect of humic acid and sodium nitroprusside on nickel toxicity in rice plants. Rice plants grown in T2 appeared green and well developed. In leaves and roots, the expression of superoxide dismutase and ascorbate peroxidase was higher in T3 (nickel-sodium nitroprusside); glutathione reductase expression in roots was lower in T1 (sand with Ni solution) compared to T2 (nickel 300 mg L-1 and HA) where the expression was higher; significant differences were found between both treatments. In leaves, the behavior of this gene was similar in all treatments. This research suggests that nickel toxicity cannot be diminished when HA or SNP are used, and they induce oxidative stress in rice plants. Key words: Nickel toxicity, heavy metals, gene expression, oxidative stress.
Highlights
Soil contamination with heavy metals like lead (Pb), Cadmium (Cd) and nickel (Ni) is an environmental problem worldwide because these metals may bioaccumulate and they do not have specific metabolic functions for living beings
The expression of superoxide dismutase and ascorbate peroxidase was higher in T3; glutathione reductase expression in roots was lower in T1 compared to T2 where the expression was higher; significant differences were found between both treatments
Reductions in plants growth and chlorosis of leaves was observed in T1 (Figure 1A) while in T2 (Ni 300 mg L-1+ humic acid (HA)) phenotypical characteristics of rice seedling like plant growth and area of leaves were better (Figure 1B) compared to T1 and T3 (Figure 1C)
Summary
Soil contamination with heavy metals like lead (Pb), Cadmium (Cd) and nickel (Ni) is an environmental problem worldwide because these metals may bioaccumulate and they do not have specific metabolic functions for living beings This pollution is mainly due to the intense industrialization and urbanization (Wei and Yang, 2010; Yaylali-Abanuz, 2011; Mireles et al, 2012). Nickel is a ubiquitous trace metal and compounds such as nickel acetate, nickel carbonate, nickel hydroxide and nickel oxide are used in a wide range of industrial processes These compounds accumulate in soil and environment, and can be absorbed by plants. Higher plants have developed a series of protective mechanisms to counteract Ni-toxicity and to control the generation of excessive reactive oxygen species (ROS) These mechanisms include anti-oxidative enzymes, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), and catalase (CAT) (Xu et al, 2010)
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