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Micronutrients, such as iron, copper, and zinc are essential for a variety of functions in the living cell. They are essential in different redox systems such as the electron transport chains of cells, organelles, and membranes, but also play an important role in DNA- and RNA-protein interaction. Deprivation of these elements is causing symptoms of deficiency, whereas excess can be toxic due to the production of reactive oxygen species and an imbalance of the cellular redox state. Both deficiency and toxicity are the cause of reduced growth and crop yields. Proteomic approaches revealed alterations of several proteins of different functional classes due to adaptation to nutrient deficiency or toxicity. General and specific responses to micronutrient deficiency and toxicity will be discussed with respect to transporters, signaling, and adaptation mechanisms.

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.

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.

Iron (Fe) homeostasis is essential for life and has been intensively investigated for dicots, while our knowledge for species in the Poaceae is fragmentary. This study presents the first proteome analysis (LC-MS/MS) of plasma membranes isolated from roots of 18-day old maize (Zea mays L.). Plants were grown under low and high Fe conditions in hydroponic culture. In total, 227 proteins were identified in control plants, whereas 204 proteins were identified in Fe deficient plants and 251 proteins in plants grown under high Fe conditions. Proteins were sorted by functional classes, and most of the identified proteins were classified as signaling proteins. A significant number of PM-bound redox proteins could be identified including quinone reductases, heme and copper-containing proteins. Most of these components were constitutive, and others could hint at an involvement of redox signaling and redox homeostasis by change in abundance. Energy metabolism and translation seem to be crucial in Fe homeostasis. The response to Fe deficiency includes proteins involved in development, whereas membrane remodeling and assembly and/or repair of Fe-S clusters is discussed for Fe toxicity. The general stress response appears to involve proteins related to oxidative stress, growth regulation, an increased rigidity and synthesis of cell walls and adaption of nutrient uptake and/or translocation. This article is part of a Special Issue entitled: Plant Proteomics in Europe.

Peroxidases are key player in the detoxification of reactive oxygen species during cellular metabolism and oxidative stress. Membrane-bound isoenzymes have been described for peroxidase superfamilies in plants and animals. Recent studies demonstrated a location of peroxidases of the secretory pathway (class III peroxidases) at the tonoplast and the plasma membrane. Proteomic approaches using highly enriched plasma membrane preparations suggest organisation of these peroxidases in microdomains, a developmentally regulation and an induction of isoenzymes by oxidative stress. Phylogenetic relations, topology, putative structures, and physiological function of membrane-bound class III peroxidases will be discussed.

Nowadays electron transport (redox) systems in plasma membranes appear well established. Members of the flavocytochrome b family have been identified by their nucleotide acid sequences and characterized on the transcriptional level. For their gene products functions have been demonstrated in iron uptake and oxidative stress including biotic interactions, abiotic stress factors and plant development. In addition, NAD(P)H-dependent oxidoreductases and b-type cytochromes have been purified and characterized from plasma membranes. Several of these proteins seem to belong to the group of hypothetical or unknown proteins. Low abundance and the lack of amino acid sequence data for these proteins still hamper their functional analysis. Consequently, little is known about the physiological function and regulation of these enzymes. In recent years evidence has been presented for the existence of microdomains (so-called lipid rafts) in plasma membranes and their interaction with specific membrane proteins. The identification of redox systems in detergent insoluble membranes supports the idea that redox systems may have important functions in signal transduction, stress responses, cell wall metabolism, and transport processes. This review summarizes our present knowledge on plasma membrane redox proteins and discusses alternative strategies to investigate the function and regulation of these enzymes.