Impact of nickel on grapevine (Vitis vinifera L.) root plasma membrane, ROS generation, and cell viability

The present study investigated the impact of nickel (Ni2+) on trans-membrane electrical potential (EM) and permeability properties of plasma membrane (PM) in epidermal cells of adventitious grapevine roots. The relationship between disturbances of membrane functionality and the production of superoxide anion, hydrogen peroxide and cell viability after the exposure of roots to Ni2+ was also studied. Treatments with 0.1–5 mmol L–1 NiCl2 induced a concentration-dependent transient PM depolarization, which was recovered to the initial resting potential within 50–70 min in the presence of Ni2+. Longer (up to 24 h) exposure of roots to 1 mmol L–1 of Ni2+ hyperpolarized the EM by approximately 17 mV. Application of the highest 5 mmol L–1 concentration of Ni2+ during longer treatments (up to 48 h) resulted in the increase of membrane permeability; however the EM, cell viability, and superoxide content remained unaffected. The increase in the formation of hydrogen peroxide was timeand concentrationdependent and maximum production was recorded after 180 min of Ni2+ treatment. We can conclude that oxidative stress resulting from an imbalance in the generation and/ or removal of hydrogen peroxide in the root tissues of grapevine was the major cause of Ni2+ toxicity.