The active oxygen species (AOS) that are deleterious molecules for living organisms serve as signaling factor to regulate the reduction/oxidation (redox) states in their cells. Since the redox status regulates many physiological processes, including environmental stress responses, AOS metabolism is carried out by a complex cross-talk of reactions involved in antioxidative enzymes and compounds with redox properties. Therefore, living organisms have developed the AOS metabolic systems in their each organelle. In higher plants, vitamin C (L-ascorbate: AsA) can accumulate to millimolar concentrations in their tissues and is associated with the regulation of the redox status as a radical scavenger and as an enzyme cofactor. In particular, plants possess ascorbate peroxidase (APX) isoenzymes that are distributed in several organelles and play important roles in the metabolism of H_2O_2. Nucleoside diphosphates derivates (Nudix: nwcleoside diphosphates linked to some moiety X), such as dinucleoside polyphosphates, ADP-ribose, NADH, nucleotide sugars, or ribo- and deoxy-nucleoside triphophates, contain the molecules toxic to the cells and the molecules with redox properties. Notably, oxidized forms of the free (deoxy)ribo nucleotide, such as 8-oxo-(d)GTP and 2-OH-(d)ATP, cause the mutation of DNA or mRNA. Therefore, Nudix hydrolases function in the precisely regulation of the intracellular levels of these molecules. In the present paper, the focus will be on recent findings concerning the physiological function of the redox signaling and its regulation by AsA, APX and Nudix hydrolases in higher plants.

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