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The plant produces excessive amounts of hydrogen peroxide (H2O2) in response to environmental stress H2O2 which causes oxidative stress and cellular damage. To cope with oxidative stress, plants express the Ascorbate peroxidase (APX) enzyme for scavenging excessive amounts of H2O2 in the cell. Among eight APX isozymes in Arabidopsis, APX2 is less studied in response to heavy metal stress. In the present study, we isolate two T-DNA insertion mutants from collection resources, named apx2-1 and apx2-2. The T-DNA was inserted in the first and fifth exon of the APX2 gene in the apx2-1 and apx2-2 mutant plants, respectively. RNA expression analysis shows that the APX2 transcript was undetectable in the mutants, indicating that both were knock-out mutants. Overexpression lines were also generated by expressing APX2 cDNA under the control of constitutive promoter 35S-CaMV in Arabidopsis. Under normal conditions, without any stress treatment that can induce the expression of endogenous AtAPX2 protein, overexpression and mutant lines did not show any distinctive phenotype compared to their WT. However, when plants were challenged with heavy metals nickel, both apx2-1 and apx2-2 showed growth retardation, browning, and died compared to WT, indicating that the mutant is more susceptible compared to WT. The browning leaves indicated that plants were dying because of the accumulation of H2O2. However, the overexpression line has more green leaves than WT and mutants under nickel treatment, indicating that the overexpression line is more tolerant to nickel than WT and mutants. This finding indicates that APX2 possibly plays a role in scavenging H2O2 due to heavy metal stress, especially nickel. APX2 can be used as a candidate gene for producing heavy metal tolerant plants in phytoremediation studies. [ABSTRACT FROM AUTHOR]