ABSTRACT
Ascorbic acid oxidase (AAO) is a plant blue-copper protein catalyzing dioxygen reduction to water using ascorbic acid as the electron donor. In spite of extensive molecular characterization the physiological role of AAO is still uncertain. Abundant mRNA, protein and activity of AAO were observed in illuminated leaves of Cucurbita pepo. AAO activity was found to be proportional to light intensity. The light effect was rapidly reversed in dark and activity remained low throughout the dark period. Activity was elicited in dark by increased oxygen concentration. AAO activity increased in the facultative CAM Kalanchoë blossfeldiana upon induction of the CAM cycle and decreased during germination of C. pepo and Zea mays under hypoxic conditions. These results strongly suggest that AAO activity could be part of a dynamic system for oxygen management in plants.
Subject(s)
Ascorbic Acid/metabolism , Light , Oxidoreductases/metabolism , Oxygen/metabolism , Plant Leaves/enzymology , Plant Proteins/metabolism , Cell Hypoxia , Cucurbita/cytology , Cucurbita/enzymology , Cucurbita/genetics , Gene Expression Regulation, Plant , Kalanchoe/cytology , Kalanchoe/enzymology , Kalanchoe/genetics , Oxidoreductases/genetics , Oxidoreductases/physiology , Oxygen/physiology , Plant Leaves/genetics , Plant Proteins/geneticsABSTRACT
To understand the function of ascorbic acid (ASC) in root development, the distribution of ASC, ASC oxidase, and glutathione (GSH) were investigated in cells and tissues of the root apex of Cucubita maxima. ASC was regularly distributed in the cytosol of almost all root cells, with the exception of quiescent centre (QC) cells. ASC also occurred at the surface of the nuclear membrane and correspondingly in the nucleoli. No ASC could be observed in vacuoles. ASC oxidase was detected by immunolocalization mainly in cell walls and vacuoles. This enzyme was particularly abundant in the QC and in differentiating vascular tissues and was absent in lateral root primordia. Administration of the ASC precursor L-galactono-gamma-lactone markedly increased ASC content in all root cells, including the QC. Root treatment with the ASC oxidized product, dehydroascorbic acid (DHA), also increased ASC content, but caused ASC accumulation only in peripheral tissues, where DHA was apparently reduced at the expense of GSH. The different pattern of distribution of ASC in different tissues and cell compartments reflects its possible role in cell metabolism and root morphogenesis.
Subject(s)
Ascorbate Oxidase/metabolism , Ascorbic Acid/metabolism , Cucurbita/metabolism , Glutathione/metabolism , Plant Roots/metabolism , Amaryllidaceae Alkaloids/pharmacology , Cell Membrane/metabolism , Cell Wall/metabolism , Cucurbita/drug effects , Cucurbita/ultrastructure , Dehydroascorbic Acid/pharmacology , Phenanthridines/pharmacology , Plant Roots/drug effects , Plant Roots/ultrastructure , Seedlings/metabolism , Sugar Acids/pharmacology , Tissue Distribution , Vacuoles/metabolismABSTRACT
Vitamin C (ascorbic acid (AA)) is very popular for its antioxidant properties. Consequently, many other important aspects of this multifaceted molecule are often underestimated or even ignored. In the present paper, we have tried to bring to the foreground some of these aspects, including the peculiarities of the AA biosynthetic pathway in different organisms, the remarkable function of AA as a co-substrate of many important dioxygenases, the role of AA-regenerating enzymes and the known pathways of AA catabolism, as well as the intriguing function of AA in gene expression.
