Plant peroxidases are involved in numerous cellular processes in plant development and stress responses. Four plasma membrane-bound peroxidases have been identified and characterized in maize (Zea mays L.) roots. In the present study, maize seedlings were treated with different stresses and signal compounds, and a functional analysis of these membrane-bound class III peroxidases (pmPOX1, pmPOX2a, pmPOX2b, and pmPOX3) was carried out. Total guaiacol peroxidase activities from soluble and microsomal fractions of maize roots were compared and showed weak changes. By contrast, total plasma membrane and washed plasma membrane peroxidase activities, representing peripheral and integral membrane proteins, revealed strong changes after all of the stresses applied. A proteomic approach using 2D-PAGE analysis showed that pmPOX3 was the most abundant class III peroxidase at plasma membranes of control plants, followed by pmPOX2a >pmPOX2b >pmPOX1. The molecular mass (63 kDa) and the isoelectric point (9.5) of the pmPOX2a monomer were identified for the first time. The protein levels of all four enzymes changed in response to multiple stresses. While pmPOX2b was the only membrane peroxidase down-regulated by wounding, all four enzymes were differentially but strongly stimulated by methyl jasmonate, salicylic acid, and elicitors (Fusarium graminearum and Fusarium culmorum extracts, and chitosan) indicating their function in pathogen defence. Oxidative stress applied as H2O2 treatment up-regulated pmPOX2b >pmPOX2a, while pmPOX3 was down-regulated. Treatment with the phosphatase inhibitor chantharidin resulted in distinct responses.

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Class III peroxidases are heme-containing proteins of the secretory pathway with an extremely high number of isoenzymes, indicating the tremendous and important functions of this protein family. This chapter describes fractionation of the cell in subproteomes, their separation by polyacrylamide gel electrophoresis (PAGE) and visualization of peroxidase isoenzymes by heme and specific in-gel staining procedures. Soluble and membrane-bound peroxidases were separated by differential centrifugation. Aqueous polymer two-phase partitioning and discontinuous sucrose density gradient were applied to resolve peroxidase profiles of plasma membranes and tonoplast. Peroxidase isoenzymes of subproteomes were further separated by PAGE techniques such as native isoelectric focussing (IEF), high resolution clear native electrophoresis (hrCNE), and modified sodium dodecyl sulfate (modSDS)-PAGE. These techniques were used as stand-alone method or in combination for two-dimensional PAGE.

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