Nickel (Ni) is an essential element for many organisms; however, it is very toxic at high concentrations
and also depending on the species. In macrofungi the mechanisms underlying their Ni
tolerance are poorly documented. This study examines, for the first time, the participation of the
antioxidative system in Macrolepiota procera exposed to different Ni2+
concentrations and their
relation with Ni tolerance. The effect of the pH on Ni tolerance was also evaluated. The fungus was
cultivated on solid medium with different NiCl2 concentrations (0.05, 0.2, 0.8 mM) at pH 4, 6, and 8,
and fungi growth and Ni uptake were determined. The antioxidative enzymes catalase (CAT) and
superoxide dismutase (SOD) and the production of hydrogen peroxide (H2O2) were evaluated on
fungal submerged cultures within the first hours of Ni2+
exposure. Results showed that M. procera
growth decreased when Ni2+
concentrations increased, reaching a maximum growth inhibition
(>80%) up to 0.2 mM of NiCl2. Ni uptake increased proportionally to Ni increase in the medium. Both
Ni tolerance and Ni accumulation were affected by medium pH. Microscope observations showed
differences in the size of spores produced by fungi at different Ni concentrations. Ni exposure
induced oxidative stress, as indicated by the production of H2O2, the levels of which seem to be
regulated by the antioxidant enzymes SOD and CAT. The time variation pattern of SOD and CAT
activities indicated that the former has a greater role in alleviating the stress. The results obtained
suggested that tolerance of M. procera to Ni2+
is associated with the ability of this macrofungus to
initiate an efficient antioxidant defense system
