Effect of hydrogen peroxide on growth and activity of some enzymes involved in proline metabolism of sweet corn seedlings under copper stress

CuCl 2 treatments led to a significant growth reduction, while pre-treatment with H 2 O 2 increased plant growth compared to the control in sweet corn seedlings. The increment of the proline content in shoots followed in the order of H 2 O 2 (6 h) + CuCl 2 > H 2 O 2 > CuCl 2 > Control. During only H 2 O 2 treatments the activities of Δ 1 -pyrroline-5-carboxylatesynthetase (P5CS) and glutamate dehydrogenase (GDH) of the glutamate path increased immediately, while Arginase and ornithine aminotransferase (OAT) of the ornithine path activities raised after 8 h treatments. Under CuCl 2 stress Arginase and OAT activities rose quickly, P5CS and GDH activities also increased after 8 h treatments. The simultaneous increase of the proline content during CuCl 2 stress might be related with the sequential activation of the ornithine and glutamate pathways and a reduction in ProDH. Pre-treatment with H 2 O 2 induced an almost immediate and rapid increase of activities of Arginase and OAT, P5CS and GDH. The treatments also decreased the activity of proline dehydrogenase, a key enzyme of proline degradation. At the same time, pre-treatment with H 2 O 2 induced an additional increase of the enzymes expression of ornithine pathway and glutamate pathway, while an additional decline was also observed in the expression of ProDH in sweet corn seedling under CuCl 2 stress. While pre-treated with H 2 O 2 under CuCl 2 stress inducing proline content was a combined result of activation of the ornithine and glutamate pathways and a reduction in ProDH. It was, therefore, concluded that H 2 O 2 ameliorated the stress generated by CuCl 2 through the enhancing proline content. Overall, the adverse effects of CuCl 2 stress could be alleviated by exogenous application of H 2 O 2 .