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      Unraveling Morphophysiological and Biochemical Responses of Triticum aestivum L. to Extreme pH: Coordinated Actions of Antioxidant Defense and Glyoxalase Systems

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          Abstract

          Soil pH, either low (acidity) or high (alkalinity), is one of the major constraints that affect many biochemical and biological processes within the cell. The present study was carried out to understand the oxidative damage and antioxidant defense in wheat ( Triticum aestivum L. cv. BARI Gom-25) grown under different pH regimes. Eight-day-old seedlings were exposed to growing media with different pH levels (4.0, 5.5, 7.0, and 8.5). Seedlings grown in pH 4.0 and in pH 8.5 showed reductions in biomass, water, and chlorophyll contents; whereas plants grown at pH 7.0 (neutral) exhibited a better performance. Extremely acidic (pH 4.0) and/or strongly alkaline (pH 8.5)-stress also increased oxidative damage in wheat by excess reactive oxygen species (ROS) generation and methylglyoxal (MG) production, which increased lipid peroxidation and disrupted the redox state. In contrary, the lowest oxidative damage was observed at a neutral condition, followed by a strong acidic condition (pH 5.5), which was mainly attributed to the better performance of the antioxidant defense and glyoxalase systems. Interestingly, seedlings grown at pH 5.5 showed a significant increase in morphophysiological attributes compared with extreme acidic (pH 4.0)- and strong alkaline (pH 8.5)-stress treatments, which indicates the tolerance of wheat to the acidic condition.

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          Most cited references43

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          Rapid determination of free proline for water-stress studies

          Plant and Soil, 39(1), 205-207
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            Regulation of cyclic and linear electron flow in higher plants.

            Cyclic electron flow is increasingly recognized as being essential in plant growth, generating a pH gradient across thylakoid membrane (ΔpH) that contributes to ATP synthesis and triggers the protective process of nonphotochemical quenching (NPQ) under stress conditions. Here, we report experiments demonstrating the importance of that ΔpH in protecting plants from stress and relating to the regulation of cyclic relative to linear flow. In leaves infiltrated with low concentrations of nigericin, which dissipates the ΔpH without significantly affecting the potential gradient, thereby maintaining ATP synthesis, the extent of NPQ was markedly lower, reflecting the lower ΔpH. At the same time, the photosystem (PS) I primary donor P700 was largely reduced in the light, in contrast to control conditions where increasing light progressively oxidized P700, due to down-regulation of the cytochrome bf complex. Illumination of nigericin-infiltrated leaves resulted in photoinhibition of PSII but also, more markedly, of PSI. Plants lacking ferredoxin (Fd) NADP oxidoreductase (FNR) or the polypeptide proton gradient regulation 5 (PGR5) also show reduction of P700 in the light and increased sensitivity to PSI photoinhibition, demonstrating that the regulation of the cytochrome bf complex (cyt bf) is essential for protection of PSI from light stress. The formation of a ΔpH is concluded to be essential to that regulation, with cyclic electron flow playing a vital, previously poorly appreciated role in this protective process. Examination of cyclic electron flow in plants with a reduced content of FNR shows that these antisense plants are less able to maintain a steady rate of this pathway. This reduction is suggested to reflect a change in the distribution of FNR from cyclic to linear flow, likely reflecting the formation or disassembly of FNR-cytochrome bf complex.
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              Redox homeostasis, antioxidant defense, and methylglyoxal detoxification as markers for salt tolerance in Pokkali rice.

              To identify biochemical markers for salt tolerance, two contrasting cultivars of rice (Oryza sativa L.) differing in salt tolerance were analyzed for various parameters. Pokkali, a salt-tolerant cultivar, showed considerably lower level of H(2)O(2) as compared to IR64, a sensitive cultivar, and such a physiology may be ascribed to the higher activity of enzymes in Pokkali, which either directly or indirectly are involved in the detoxification of H(2)O(2). Enzyme activities and the isoenzyme pattern of antioxidant enzymes also showed higher activity of different types and forms in Pokkali as compared to IR64, suggesting that Pokkali possesses a more efficient antioxidant defense system to cope up with salt-induced oxidative stress. Further, Pokkali exhibited a higher GSH/GSSG ratio along with a higher ratio of reduced ascorbate/oxidized ascorbate as compared to IR64 under NaCl stress. In addition, the activity of methylglyoxal detoxification system (glyoxalase I and II) was significantly higher in Pokkali as compared to IR64. As reduced glutathione is involved in the ascorbate-glutathione pathway as well as in the methylglyoxal detoxification pathway, it may be a point of interaction between these two. Our results suggest that both ascorbate and glutathione homeostasis, modulated also via glyoxalase enzymes, can be considered as biomarkers for salt tolerance in Pokkali rice. In addition, status of reactive oxygen species and oxidative DNA damage can serve as a quick and sensitive biomarker for screening against salt and other abiotic stresses in crop plants.
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                Author and article information

                Journal
                Plants (Basel)
                Plants (Basel)
                plants
                Plants
                MDPI
                2223-7747
                18 January 2019
                January 2019
                : 8
                : 1
                : 24
                Affiliations
                [1 ]Laboratory of Plant Stress Response, Department of Applied Biological Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kita-gun, Kagawa 761-0795, Japan; razon_sau@ 123456yahoo.com (M.H.M.B.B.); shahadatsau24@ 123456gmail.com (M.S.H.)
                [2 ]Citrus Research Station, Bangladesh Agricultural Research Institute, Jaintapur, Sylhet 3156, Bangladesh
                [3 ]Department of Agronomy, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh; mhzsauag@ 123456yahoo.com
                [4 ]Department of Agroforestry and Environmental Science, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh; jamahmud_bd@ 123456yahoo.com
                [5 ]Department of Agricultural Botany, Sher-e-Bangla Agricultural University, Dhaka 1207, Bangladesh; farhatasnim28@ 123456gmail.com
                Author notes
                [* ]Correspondence: fujita@ 123456ag.kagawa-u.ac.jp ; Tel.: +81-87-891-3033
                Author information
                https://orcid.org/0000-0002-7602-3087
                Article
                plants-08-00024
                10.3390/plants8010024
                6359243
                30669317
                988a4605-d664-41db-bde2-4345fbea0afc
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 19 December 2018
                : 15 January 2019
                Categories
                Article

                acidity,alkalinity,antioxidant defense,methylglyoxal,phytotoxicity,reactive oxygen species

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