Fingerprinting of the antioxidant status in Alyssum markgrafii shoots during nickel hyperaccumulation in vitro

This study investigated the role of antioxidant system of Alyssum markgrafii, during long-term exposure to 0.5 or 1 mM NiCl2 × 6H2O in vitro. Applied methodology included sample preparation protocol which reduces oxidation of key metabolites along with novel luminescent method and well-established photometric procedures. During 5-week treatments, plants accumulated 1121 and 2470 ppm of Ni2+ respectively, followed by severe growth retardation, chlorophyll degradation and peroxidation of lipids. These effects were more pronounced after 1 mM Ni2+ treatment and additionally accompanied by increased water loss. Activities of luminol-converting peroxidases and glutathione reductase upon 0.5 mM treatment were increased while catalase and superoxide dismutase were diminished. The fact that these two groups of enzymes run in antiparallel might suggest functional redistribution between antioxidant enzymes rather than orchestrated action to prevent oxidative damage. Total antioxidant capacity (TAC) was also increased after 0.5 mM treatment which coincided with increased GR activity and elevated glutathione content indicating this low molecular weight antioxidant as an important factor associated with nickel tolerance. This study also emphasizes the possible important role of luminol-converting peroxidases in nickel hyperaccumulation, although they are not considered as antioxidant enzymes sensu stricto since some of them can also produce reactive oxygen species as well.