Early cadmium-induced effects on reactive oxygen species production, cell viability and membrane electrical potential in grapevine roots
Cadmium (Cd) is one of the most worldwide concerned metal pollutants. It is able to induce reactive oxygen species production through indirect mechanisms causing oxidative stress. Vitis vinifera roots were treated with 100 μM Cd for 0-180 min or 20-100 μM Cd for 24 h. Fluorescence confocal microscopy showed elevated hydrogen peroxide and superoxide levels in the apical root segments. Two phases (after 30 min and 24 h) of the superoxide raised levels were observed. This was accompanied by the decrease in root cell viability. Cd in concentrations between 0.005-10 mM induced significant, but different changes in membrane electrical potential (EM) of the root epidermal cells. The low concentrations of Cd (0.005-0.01 mM) caused transient EM hyperpolarization followed by depolarization, whereas by higher concentrations (0.05-5.0 mM) EM was depolarized. In any case, the depolarization or hyperpolarization were only transient up to 5 mM Cd concentration indicating that the plasma membrane function was not irreversibly destroyed. Hyperpolarization of EM induced by fusicoccin (FC) was completely suppressed only in the presence of 10 mM Cd pointing to the inhibition of H+-ATPase. The results suggest that the Cd interactions, depending on cellular development, result in activation of a complex of various mechanisms such as peroxide and hydrogen peroxide production, which in turn may be a more probable reason for the root cell responses to Cd toxicity than the transient EM changes.
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