Exogenous cadaverine induces oxidative burst and reduces cadaverine conjugate content in the common ice plant

The effect of free cadaverine (Cad) on its conjugates formation was analyzed in roots of the common ice plants (Mesembryanthemum crystallinum L.). It was found for the first time that Cad could induce oxidative burst in the roots of adult plants, as was evident from the sharp decrease in the content of Cad soluble or insoluble conjugates. This unusual effect was associated with the increased oxidative degradation of exogenous Cad (1 mM, 1.5 h) and intense H2O2 production in the root cells of adult plants. Root treatment of both juvenile and adult plants with H2O2 (1 mM, 1.5 h) reduced the content of soluble Cad conjugates and increased the content of their components, free Cad and phenols. We also found that one of the possible reasons of the negative effect of exogenous diamine on the formation of conjugated forms in adult roots was alkalization of the root apoplast at Cad addition to nutrient medium and the unusual O2 {radical dot}- synthase function as a pH-dependent guaiacol peroxidase in the presence of a high content of H2O2. This was confirmed by the data on the accumulation of O2 {radical dot}- and enhanced superoxide dismutase activity in adult roots under treatment with Cad. It is possible that the accumulation of O2 {radical dot}- together with H2O2 was also responsible for oxidative burst, which induced a decrease in the content of Cad conjugates in adult roots of the common ice plants. © 2008