Early production of activated oxygen species in root apoplast of wheat following copper excess

Wheat seedlings (Triticum durum Desf.) were incubated in a solution containing 100 μM CuSO4 for increasing time ranging from 1 min to 6 h. Copper rapidly accumulated into the roots, and its amount increased significantly until 360 min. During the experiment, copper did not cause any lipid peroxidation and K+ leakage. Up to 60 min of copper treatment the superoxide (O2radical dot−) production in root apoplast decreased concomitantly with increase in superoxide dismutase (SOD) activity. In contrast, after 60 min of incubation, SOD decreased and this facilitated an increase in O2radical dot− production. In the presence of the SOD inhibitor diethyldithiocarbamic acid, O2radical dot− production was more than two times higher and showed a biphasic increase. Very high SOD activity in the apoplast, due to the presence of three different isozymes, one Mn-SOD and two CuZn-SODs, dismutated the radical giving rise, at least in part, to an increase in hydrogen peroxide. The highest value of H2O2 was detected at 15 min, when peroxidase (POD) activity reached the lowest value. Root apoplast showed the presence of at least five different isoforms of PODs, whose pattern did not change during the entire treatment.