Linking hydrogen-mediated boron toxicity tolerance with improvement of root elongation, water status and reactive oxygen species balance: a case study for rice
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Background and aims Boron is essential for plant growth but hazardous when present in excess. As the antioxidant properties of hydrogen gas (H2) were recently described in plants, oxidative stress induced by excess boron was investigated along with other biological responses during rice (Oryza sativa) seed germination to study the beneficial role of H2. Methods Rice seeds were pretreated with exogenous H2. Using physiological, pharmacological and molecular approaches, the production of endogenous H2, growth status, reactive oxygen species (ROS) balance and relative gene expression in rice were measured under boron stress to investigate mechanisms of H2-mediated boron toxicity tolerance. Key Results In our test, boron-inhibited seed germination and seedling growth, and endogenous H2 production, were obviously blocked by exogenously applying H2. The re-establishment of ROS balance was confirmed by reduced lipid peroxidation and ROS accumulation. Meanwhile, activities of catalase (CAT) and peroxidase (POX) were increased. Suppression of pectin methylesterase (PME) activity and downregulation of PME transcripts by H2 were consistent with the alleviation of root growth inhibition caused by boron. Water status was improved as well. This result was confirmed by the upregulation of genes encoding specific aquaporins (AQPs), the maintenance of low osmotic potential and high content of soluble sugar. Increased transcription of representative AQP genes (PIP2;7 in particular) and BOR2 along with decreased BOR1 mRNA may contribute to lowering boron accumulation. Conclusions Hydrogen provides boron toxicity tolerance mainly by improving root elongation, water status and ROS balance.Significance Aquaporins are known for their capacity to increase transcellular water exchange. In plants, a highly conserved group known as plasma membrane intrinsic proteins (PIP) affects the adjustment of not only membrane water permeability but also overall plant hydraulic conductivity. An experimental design combined with a mathematical modeling approach allowed us to explore the interplay of channel gating, membrane translocation, and channel stoichiometric arrangement of a pair of PIP1 and PIP2 aquaporins. We dissect the individual contribution of each PIP, showing that ( i ) PIP1 has a high water transport capacity when coexpressed with PIP2, ( ii ) PIP2 water permeability is enhanced if it physically interacts with PIP1, and ( iii ) the PIP1–PIP2 interaction results in the formation of heterotetramers with random stoichiometric arrangement.
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Abstract Based on a comparison with the activity of fresh potato enzyme extracts, complete recovery of phenolase, peroxidase and catalase activity was obtained from either freeze‐dried tissue or powder obtained by grinding the tissue with acetone. Phenolase activity was stable for 1 year, peroxidase for 2–4 weeks and catalase for 8 weeks.
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Lipid peroxidation and serum catalase activity were assessed in 63 chronic alcoholics. 41 of them had renal lesions. The latter had more profound inhibition of blood serum catalase activity and distinct enhancement of lipid peroxidation. A reverse correlation exists between low catalase activity and lipid peroxidation activation in chronic alcoholics.
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The capacity of roots to take up water is determined in part by the resistance of living tissues to radial water flow. Both the apoplastic and cell‐to‐cell paths mediate water transport in these tissues but the contribution of cell membranes to the latter path has long been difficult to estimate. Aquaporins are water channel proteins that are expressed in various membrane compartments of plant cells, including the plasma and vacuolar membranes. Plant aquaporins are encoded by a large multigene family, with 35 members in Arabidopsis thaliana, and many of these aquaporins show a cell‐specific expression pattern in the root. Mercury acts as an efficient blocker of most aquaporins and has been used to demonstrate the significant contribution of water channels to overall root water transport. Aquaporin‐rich membranes may be needed to facilitate intense water flow across root tissues and may represent critical points where an efficient and spatially restricted control of water uptake can be exerted. Roots, in particular, show a remarkable capacity to alter their water permeability over the short term (i.e. in a few hours to less than 2–3 d) in response to many stimuli, such as day/night cycles, nutrient deficiency or stress. Recent data suggest that these rapid changes can be mostly accounted for by changes in cell membrane permeability and are mediated by aquaporins. Although the processes that allow perception of environmental changes by root cells and subsequent aquaporin regulation are nearly unknown, the study of root aquaporins provides an interesting model to understand the regulation of water transport in plants and sheds light on the basic mechanisms of water uptake by roots.
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The activities of catalase, peroxidase, indoleacetic acid (IAA) oxidase and peroxide levels in cucumber plants during and after chilling were determined. During 96 hours at 5 C and 85% relative humidity, catalase activity declined, IAA oxidase activity increased, and peroxide concentrations increased. Peroxidase activity was not affected by chilling. When chilled plants were returned to 25 C to recover, enzyme activities and peroxide concentration were restored to their prechilling levels. The increase in peroxide and IAA oxidase activity may inactivate or destroy IAA and thus retard growth.
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In the present work, the effect of NaCl on catalase and peroxidase activity of Chlorella vulgaris Beijerink was investigated The C. vulgaris was treated with different concentrations of NaCl viz., 0.1, 0.2, 0.3 and 0.4M besides control over 10, 20 and 30 days. The results exhibited increase in the catalase and peroxidase activity up to 0.3 M, whereas it was decreased at 0.4M for all the cultures over all the durations. The study revealed that, increased activity of catalase and peroxidase was an adaptive mechanism to reduce the H2O2 and offer protection against oxidative damage and tolerance against salt.
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By studying activity of Catalase and Peroxidase in cucumber leaves, the results showed that: after cold acclimation activity of Catalase and Peroxidase both increased sharply, after chilling temperature activity of Catalase on the CK decreased 35%, but that of acclimation merely reduced 3.48%.
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