title: Metal/metalloid stress tolerance in plants: role of ascorbate, its redox couple, and associated enzymes.
abstract: The enhanced generation of reactive oxygen species (ROS) under metal/metalloid stress is most common in plants, and the elevated ROS must be successfully metabolized in order to maintain plant growth, development, and productivity. Ascorbate (AsA) is a highly abundant metabolite and a water-soluble antioxidant, which besides positively influencing various aspects in plants acts also as an enigmatic component of plant defense armory. As a significant component of the ascorbate-glutathione (AsA-GSH) pathway, it performs multiple vital functions in plants including growth and development by either directly or indirectly metabolizing ROS and its products. Enzymes such as monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) maintain the reduced form of AsA pool besides metabolically controlling the ratio of AsA with its oxidized form (dehydroascorbate, DHA). Ascorbate peroxidase (APX, EC 1.11.1.11) utilizes the reduced AsA pool as the specific electron donor during ROS metabolism. Thus, AsA, its redox couple (AsA/DHA), and related enzymes (MDHAR, DHAR, and APX) cumulatively form an AsA redox system to efficiently protect plants particularly against potential anomalies caused by ROS and its products. Here we present a critical assessment of the recent research reports available on metal/metalloid-accrued modulation of reduced AsA pool, AsA/DHA redox couple and AsA-related major enzymes, and the cumulative significance of these antioxidant system components in plant metal/metalloid stress tolerance.
authors.affiliation: Centre for Environmental and Marine Studies (CESAM) and Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal, anjum@ua.pt.
authors.forename: Naser A
authors.initials: NA
authors.lastname: Anjum
authors.forename: Sarvajeet S
authors.initials: SS
authors.lastname: Gill
authors.forename: Ritu
authors.initials: R
authors.lastname: Gill
authors.forename: Mirza
authors.initials: M
authors.lastname: Hasanuzzaman
authors.forename: Armando C
authors.initials: AC
authors.lastname: Duarte
authors.forename: Eduarda
authors.initials: E
authors.lastname: Pereira
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ahmad
authors.forename: Renu
authors.initials: R
authors.lastname: Tuteja
authors.forename: Narendra
authors.initials: N
authors.lastname: Tuteja
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D001205:Ascorbic Acid / Q000378:metabolism*; D058955:Metalloids / Q000633:toxicity*; D008670:Metals / Q000633:toxicity*; D010084:Oxidation-Reduction; D010944:Plants / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D013312:Stress, Physiological / Q000187:drug effects*
chemical_list: D058955:Metalloids; D008670:Metals; D001205:Ascorbic Acid