Dehydroascorbate and dehydroascorbate reductase are phantom indicators of oxidative stress in plants

Abstract

In many physiological studies dehydroascorbate (DHA) reductase is regarded as one of the chloroplast enzymes involved in the protection against oxidative stress. Here, evidence is presented that plant cells do not possess a specific DHA reductase. The DHA reductase activities measured in plant extracts are due to side reactions of proteins containing redoxactive dicysteine sites. Native gel electrophoresis combined with specific activity staining revealed three different proteins with DHA reductase activity in leaf and chloroplast extracts. These proteins have been identified as thioredoxins and trypsin inhibitors (Kunitz type) by Western blot analysis. The essential regulatory functions of thioredoxins in chloroplast metabolism are strongly inhibited in the presence of as little as 50 μΜ DHA. Thus, the intracellular DHA concentration should be kept below 50 μΜ but not all proteins with DHA reductase activity are effective enough for this purpose. A specific DHA reductase is frequently demanded as part of the enzymatic equipment to avoid oxidative stress. We argue that this is not necessary because in chloroplasts DHA does not accumulate to any significant extent due to the high activities of monodehydroascorbate reductase and of reduced ferredoxin.

Functional Divergence in the Glutathione Transferase Superfamily in Plants

“…In plants, DHA arises from the dismutation of semi-dehydroascorbate (SDHA), the major oxidized form of ascorbate with SDHA normally recycled back to ascorbate by an NAD(P)H-dependent SDHA reductase (29). However, if SDHA is allowed to accumulate then DHA accumulates, although the importance of this reaction in planta is the subject of some debate (30,31). The isolation of DHARs predicted to be targeted to either the cytosol and chloroplast clarifies the compartmentalization of these enzymes in Arabidopsis.…”

Cytosolic and Chloroplastic DHARs Cooperate in Oxidative Stress-Driven Activation of the Salicylic Acid Pathway

“…Indeed, kinetic modeling of the chloroplast ascorbate-glutathione pathway suggested that the chemical reaction could be largely predominant (Polle, 2001). For these reasons, the physiological importance of DHARs in oxidative stress has been subject to some debate (Morell et al, 1997;Foyer and Mullineaux, 1998;Smirnoff, 2011), and the biological roles of the endogenous genes, and the relationships between them, remain to be elucidated.…”

Relationship Between Relative Water Content and Ascorbate Redox Enzymes Activity in Lettuce Leaves Subjected to Soil Water Stress

“…(Conklin, 2001;Tokugana, et al, 2005 (Foyer and Halliwell, 1976;Foyer et al, 1983;Shigeoka et al, 2002 (Shigeoka et al, 2002;Shimaoka et al, 2000;Urano et al, 2000;Yoshimura et al, 2000). 이들 효소의 활성변화에 영향을 주는 인자로는 오존처리 , 관수온도 (Kang et al, 2001), 수분부족 (Kang, 2008) 등이 있으며, 시금치 (Morell et al, 1997), 완두콩 (Leterrier et al, 2005), 토마토 (Grantz et al, 1995) )를 측정하였 다 . DHAR (EC 1.8.5.1)의 활성도는 10 mM GSH, 5 mM DHA와 조효소액을 첨가한 50 mM .…”