Antioxidative defence mechanisms in two grapevine (Vitis vinifera L.) cultivars grown under boron excess in the irrigation water

The aim of this study was to investigate the impact of B excess on the antioxidative defence system in two grapevine cultivars (cvs.) differently sensitive to B, in order to evaluate in which way the different sensitivity was correlated to the activation of defence mechanisms. Two-year-old Vitis vinifera L. plants (cvs. ‘Merlot’ and ‘Sangiovese’), grafted on the same rootstock, were subjected to B treatment as potted vines, and biochemical determinations were employed to evaluate the antioxidative response. Compared to ‘Sangiovese’, ‘Merlot’ showed a much higher B accumulation and both leaf and peroxidative damages. In B-treated ‘Sangiovese’ the activity of superoxide dismutase did not change compared to control leaves, whereas in ‘Merlot’ a dramatic decrease in the enzyme activity was observed. B increased reduced ascorbate pools in both cvs., but ascorbate peroxidase activity was enhanced only in ‘Merlot’. In this latter cv. an enhancement of total phenols was also observed. ‘Merlot’ showed a lower ability to contrast B accumulation in leaves than ‘Sangiovese’ evidencing a higher oxidative stress. Even if defence mechanisms were generally activated in ‘Merlot’, they did not counteract efficiently metabolic damages likely due to the dramatic decrease in superoxide dismutase, the first enzyme involved in the detoxification of oxygen radicals.