Effect of cadmium on the distribution of hydroxyl radical, superoxide and hydrogen peroxide in barley root tip

In the present study, we investigated the alteration of reactive oxygen species production along the longitudinal axis of barley root tips during Cd treatment. In unstressed barley root tips, H 2 O 2 production decreased from the root apex towards the differentiation zone where again, a slight increase was observed towards the more mature region of root. An opposite pattern was observed for O 2 ⋅− and OH ⋅ generation. The amount of both O 2 ⋅− and OH ⋅ was highest in the elongation zone, decreased in the root apex and at the differentiation zone of root, then increased again towards the more mature region of root. An elevated Cd-induced O 2 ⋅− production started in the elongation zone and increased further along the differentiation zone of barley root tip. In contrast, Cd-induced H 2 O 2 production was localised to the root elongation zone and to the beginning of the differentiation zone. In contrast to Cd-induced H 2 O 2 and O 2 ⋅− production, Cd reduced OH ⋅ production along the whole barley root tip. Our results suggest that not only an increase but also the spatial distribution of reactive oxygen species production is involved in the Cd-induced stress response of barley root tip.