Methodological approaches for studying apoplastic redox activity: 2. Regulation of peroxidase activity

This work is devoted to the study of mechanisms of substrate regulation of extracellular peroxidase (ECPOX) activity at a distant stress (wounding) signal transmission from aboveground organ (leaf) of wheat (Triticum aestivum L., cv. Kazanskaya Yubileinaya) seedlings to the roots. Along with the high dianizidine peroxidase activity, the extracellular solution manifested 3,4-dihydrooxi-L-phenylalanine peroxidase, ascorbate peroxidase, and catalase activities. Dianizidine peroxidases were represented by several isoforms and had broad substrate specificity. It was found that ECPOX was released from the roots into the growing solution and its activity in the solution increased with root growth. Excision of the apical leaf parts in seedlings induced a sharp activation of root ECPOX in the growing solution. The interaction between ECPOX substrates at oxidation in two- and three-component systems is demonstrated. The role of ECPOX in the control of ROS balance in the plant cell apoplast might be determined by competitive and complementary interactions between different peroxidase substrates. Such substrate-substrate regulation of peroxidase activities may be important for stress-induced oxidative burst in plant cells.