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

• The effect of H2O2 on proline metabolism in corn grown in CuCl2 was detected.
• CuCl2 stress can act the glutamate and ornithine pathways and reduce the ProDH.
• The glutamate pathway acted by CuCl2 stress was delayed to the ornithine pathway.
• H2O2 pre-treatment can increase the ornithine and glutamate pathway in CuCl2 stress.
• H2O2 pre-treatment can reduce the ProDH in CuCl2 stress.

CuCl2 treatments led to a significant growth reduction, while pre-treatment with H2O2 increased plant growth compared to the control in sweet corn seedlings. The increment of the proline content in shoots followed in the order of H2O2 (6 h) + CuCl2 > H2O2 > CuCl2 > Control. During only H2O2 treatments the activities of Δ1-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 CuCl2 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 CuCl2 stress might be related with the sequential activation of the ornithine and glutamate pathways and a reduction in ProDH. Pre-treatment with H2O2 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 H2O2 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 CuCl2 stress. While pre-treated with H2O2 under CuCl2 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 H2O2 ameliorated the stress generated by CuCl2 through the enhancing proline content. Overall, the adverse effects of CuCl2 stress could be alleviated by exogenous application of H2O2.