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Ion Leakage (ion + leakage)
Selected AbstractsInhibition of SERCA Ca2+ pumps by 2-aminoethoxydiphenyl borate (2-APB)FEBS JOURNAL, Issue 15 20022-APB reduces both Ca2+ binding, by interfering with the pathway leading to the Ca2+ -binding sites, phosphoryl transfer from ATP 2-Aminoethoxydiphenyl Borate (2-APB) has been extensively used recently as a membrane permeable modulator of inositol-1,4,5-trisphosphate-sensitive Ca2+ channels and store-operated Ca2+ entry. Here, we report that 2-APB is also an inhibitor of sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA) Ca2+ pumps, and additionally increases ion leakage across the phospholipid bilayer. Therefore, we advise caution in the interpretation of results when used in Ca2+ signalling experiments. The inhibition of 2-APB onthe SERCA Ca2+ pumps is isoform-dependent, with SERCA 2B being more sensitive than SERCA 1A (IC50 values for inhibition being 325 and 725 µm, respectively, measured at pH 7.2). The Ca2+ -ATPase is also more potently inhibited at lower pH (IC50 = 70 µm for SERCA1A at pH 6). 2-APB decreases the affinity for Ca2+ binding to the ATPase by more than 20-fold, and also inhibits phosphoryl transfer from ATP (by 35%), without inhibiting nucleotide binding. Activity studies performed using mutant Ca2+ -ATPases show that Tyr837 is critical for the inhibition of activity by 2-APB. Molecular modeling studies of 2-APB binding to the Ca2+ ATPase identified two potential binding sites close to this residue, near or between transmembrane helices M3, M4, M5 and M7. The binding of 2-APB to these sites could influence the movement of the loop between M6 and M7 (L6-7), and reduce access of Ca2+ to their binding sites. [source] Onion Cells After High Pressure and Thermal Processing: Comparison of Membrane Integrity Changes Using Different Analytical Methods and Impact on Tissue TextureJOURNAL OF FOOD SCIENCE, Issue 7 2010Maria E. Gonzalez Abstract:, Two different analytical methods were evaluated for their capacity to provide quantitative information on onion cell membrane permeability and integrity after high pressure and thermal processing and to study the impact of these processing treatments on cell compartmentalization and texture quality. To determine changes in cell membrane permeability and/or integrity the methodologies utilized were: (1) measurement of a biochemical product, pyruvate, formed as a result of membrane permeabilization followed by enzymatic activity and (2) leakage of electrolytes into solution. These results were compared to previously determined methods that quantified cell viability and 1H-NMR T2 of onions. These methods allowed for the monitoring of changes in the plasma and tonoplast membranes after high pressure or thermal processing. High pressure treatments consisted of 5 min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30 min water bath exposure to 40, 50, 60, 70, or 90 °C. There was strong agreement between the methods in the determination of the ranges of high pressure and temperature that induce changes in the integrity of the plasma and tonoplast membranes. Membrane rupture could clearly be identified at 300 MPa and above in high pressure treatments and at 60 °C and above in the thermal treatments. Membrane destabilization effects could already be visualized following the 200 MPa and 50 °C treatments. The texture of onions was influenced by the state of the membranes and was abruptly modified once membrane integrity was lost. Practical Application:, In this study, we used chemical, biochemical, and histological techniques to obtain information on cell membrane permeability and onion tissue integrity after high pressure and thermal processing. Because there was strong agreement between the various methods used, it is possible to implement something relatively simple, such as ion leakage, into routine quality assurance measurements to determine the severity of preservation methods and the shelf life of processed vegetables. [source] 1-Methylcyclopropene affects the antioxidant system of apricots (Prunus armeniaca L. cv. Búlida) during storage at low temperatureJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 4 2010Isabel Egea Abstract BACKGROUND: Apricots (Prunus armeniaca cv. Búlida) were treated with 1 mL L,1 1-methylcyclopropene (1-MCP) immediately after harvest and stored in air at 2 °C for 21 days. Antioxidant levels (ascorbic acid and carotenoids), enzymatic antioxidant activities (superoxide dismutase (SOD) and unspecific peroxidase (POX)) and total antioxidant capacity (trolox equivalent antioxidant capacity (TEAC)) were determined. The level of oxidative stress was also established by measuring ion leakage during storage. The changes in the antioxidant potential of apricots were related to the capacity of 1-MCP to increase their commercial life. RESULTS: 1-MCP-treated fruits exhibited higher SOD activity, whereas POX activity was significantly higher only after 21 days at 2 °C. Treated fruits also exhibited better retention of ascorbate and carotenoids and higher TEAC during storage. In accordance with these observations, lower ion leakage values were detected in 1-MCP-treated apricots. CONCLUSION: Taken together, these results suggest that 1-MCP conferred a greater resistance to oxidative stress. This, along with the reduction in ethylene production, could contribute to the increase in commercial life and nutritional value observed in 1-MCP-treated apricots. Copyright © 2010 Society of Chemical Industry [source] Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterolsPLANT CELL & ENVIRONMENT, Issue 1 2010FEDERICO J. BERLI ABSTRACT We investigated the interactions of abscisic acid (ABA) in the responses of grape leaf tissues to contrasting ultraviolet (UV)-B treatments. One-year-old field-grown plants of Vitis vinifera L. were exposed to photosynthetically active radiation (PAR) where solar UV-B was eliminated by using polyester filters, or where PAR was supplemented with UV-B irradiation. Treatments combinations included weekly foliar sprays of ABA or a water control. The levels of UV-B absorbing flavonols, quercetin and kaempferol were significantly decreased by filtering out UV-B, while applied ABA increased their content. Concentration of two hydroxycinnamic acids, caffeic and ferulic acids, were also increased by ABA, but not affected by plus UV-B (+UV-B) treatments. Levels of carotenoids and activities of the antioxidant enzymes, catalase, ascorbate peroxidase and peroxidase were elevated by +ABA treatments, but only if +UV-B was given. Cell membrane , -sitosterol was enhanced by ABA independently of +UV-B. Changes in photoprotective compounds, antioxidant enzymatic activities and sterols were correlated with lessened membrane harm by UV-B, as assessed by ion leakage. Oxidative damage expressed as malondialdehyde content was increased under +UV-B treatments. Our results suggest that the defence system of grape leaf tissues against UV-B is activated by UV-B irradiation with ABA acting downstream in the signalling pathway. [source] Overexpression of bacterial catalase in tomato leaf chloroplasts enhances photo-oxidative stress tolerancePLANT CELL & ENVIRONMENT, Issue 12 2003E.-A. MOHAMED ABSTRACT The Escherichia coli gene katE, which is driven by the promoter of the Rubisco small subunit gene of tomato, rbcS3C, was introduced into a tomato (Lycopersicon esculentum Mill.) by Agrobacterium tumefaciens -mediated transformation. Catalase activity in progeny from transgenic plants was approximately three-fold higher than that in wild-type plants. Leaf discs from transgenic plants remained green at 24 h after treatment with 1 µm paraquat under moderate light intensity, whereas leaf discs from wild-type plants showed severe bleaching after the same treatment. Moreover, ion leakage from transgenic leaf discs was significantly less than that from wild-type leaf discs at 24 h after treatment with 1 µm paraquat and 10 mm H2O2, respectively, under moderate light intensity. To evaluate the efficiency of the E. coli catalase to protect the whole transgenic plant from the oxidative stress, transgenic and wild-type plants were sprayed with 100 µm paraquat and exposed to high light illumination (800 µmol m,2 s,1). After 24 h, the leaves of the transgenic plants were less damaged than the leaves of the wild-type plants. The catalase activity and the photosynthesis activity (indicated by the Fv/Fm ratio) were less affected by paraquat treatment in leaves of transgenic plants, whereas the activities of the chloroplastic ascorbate peroxidase isoenzymes and the ascorbate content decreased in both lines. In addition, the transgenic plants showed increased tolerance to the oxidative damage (decrease of the CO2 fixation and photosystem II activity and increase of the lipid peroxidation) caused by drought stress or chilling stress (4 °C) under high light intensity (1000 µmol m,2 s,1). These results indicate that the expression of the catalase in chloroplasts has a positive effect on the protection of the transgenic plants from the photo-oxidative stress invoked by paraquat treatment, drought stress and chilling stress. [source] | ||||||||||