1,721,104 research outputs found
Alterazioni delle membrane biologiche indotte da stress idrico: le proteine
No full textThe most important functions of the plant cell depend on the functionality of its membranes which is impaired if proteins and lipids are damaged. When water content reaches a value below 20% membrane dry weight, proteins undergo functional and quali-quantitative alterations. Functional alterations involve changes in protein mobility and in the conformational status and they may be analysed by electron spin resonance (ESR) technique. Following water stress membrane proteins have a lower mobility (as it is shown by the higher rotational correlation time in comparison with the control values) and the oxidation of the SH-groups occurs. As a consequence, the functionality of the proteins which need conformational changes to exert their action is impaired. Under water stress there is a reduction of preformed polyribosome and /or the preferential synthesis of "stress proteins" causing quali-quantitative alterations of membrane proteins. For this reason, water deficit determines changes in total membrane proteins, polypeptide composition as well as in the protein/lipid, hydrophilic protein/hydrophobic protein and protein/chlorophyll ratios. However, plants possess defence mechanisms which allow them to maintain structural integrity of membrane and to avoid damages caused by activated oxygen species such as superoxide anion radical and hydrogen peroxide, whose production increases under water deficit conditions. Antioxidants such as ascorbic acid and glutathione as well as the enzymes related to their metabolism (ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase) remove these toxic species by the glutathione/ascorbate cycle before membranes and the SH-groups of proteins are damaged
Glutathione/ascorbate cycle and its interelation with lipoic acid: could it explain why plants do not get cancer?
No full textSunflower seedlings subjected to incresing water deficit stress: oxidative stress and defence mechanisms
No full textSunflower seedlings (Helianthus annuus cv. Licia Stella) reached a mild, moderate and severe level of water deficit stress after 5,8 and 11 days of soil water depletion, respectively. At a moderate level of water deficit stress, an elestic adjustment occurred. At the same time, in response to a minor osmotic potential and an intermediate rate of water potential decrease, glutathione level increased and enzyme activities related to the ascorbate/glutathione cycle were induced. At severe water deficit stress, the efficiency of this defence mechanism fell, oxidative processes intensified and soluble protein content decreased further. The results of the present experiment suggest that during water deficit stress the water status of the plants plays a key role in the activation of defence mechanisms
The role of dietary chlorophylls: an EPR study on the antioxidant activities of tomato lipid extracts
No full textIdentification of the components responsible for the antioxidant activity of lipid extracts from tomato with some lipid antioxidants was obtained by EPR using the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH). Lipid extracts were obtained from leaves, roots and berries of tomato grown in hydroponics. Both fast lipophilic antioxidants (FLA) and slow lipophilic antioxidants (SLA) were present in leaves and berries whereas only SLA could be identified in the root lipid extract. Simulation of the decay kinetic of DPPH by leaves was obtained with a chlorophyll b/β-carotene mixture whereas lycopene, which reduced DPPH with a stoichiometry 1:1, behaved as a SLA. Antioxidant activity of lipid extract from leaves showed values 56-and 45-fold higher than the antioxidant activity of lipid extract from root and berries, respectively and it was mainly due to the presence of chlorophyll, representing in the leaf 38% of FLA
Antioxidant potential in lipophilic and hydrophilic extracts from medicinal herbs (Salvia officinalis and Echinacea angustifolia). A comparison between assays based on electron paramagnetic resonance and spectrophotometry
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Antioxidative responses in Vitis vinifera infected by grapevine fanleaf virus
No full textThe antioxidative response of grapevine leaves (Vitis vinifera cv. Trebbiano) affected by the presence of grapevine fanleaf virus was studied during the summer of 2010 at three different harvest times (July 1st and 26th, and August 30th). At the first and second harvest, infected leaves showed increases in the concentration of superoxide radical and hydrogen peroxide, the latter increasing for enhanced activity of superoxide dismutase. In contrast, at the last harvest time, increases in the ascorbate pool and ascorbate peroxidase activity maintained hydrogen peroxide to control levels. The glutathione pool was negatively affected as summer progressed, showing a decrease in its total and reduced form amounts. At the same time, increases in the ascorbate pool were observed, making antioxidant defenses of grapevine effective also at the last harvest time. Increases in phenolic acids, and in particular in p-hydroxybenzoic acid, at the first and second harvest might have enhanced the efficiency of the antioxidant system through an interrelation between a peroxidase/phenol/ascorbate system and the NADPH/glutathione/ascorbate cycle. The lack of increase in p-hydroxybenzoic acid at the third harvest could be due instead to the enhanced utilization of this acid for hydrogen peroxide detoxification. With time, grapevine plants lost their capacity to contrast the spread of grapevine fanleaf virus, but acquired a greater ability to counteract pathogen-induced oxidative stress, being endowed with more reduced antioxidant pools
Sunflower seedlings subjected to increasing stress by water deficit: Changes in superoxide production related to the composition of thylakoid membranes
No full textFree radicals, such as the superoxide anion, can damage the photosynthetic apparatus. At the same time they are increasingly formed as by-products of electron transport during stress conditions. For this reason, we studied the kinetics of formation and decay of superoxide anions in relation to changes, induced by increasing water deficit, in the composition of thylakoids. Seedlings of sunflower (Helianthus annuus L. cv. Licia Stella) were subjected to either a mild, a moderate, or a severe water deficit. Upon illumination of thylakoid membranes containing Tiron, we found first order kinetics of formation and decay of the Tiron semiquinone radical. At each stress intensity a higher rate of superoxide formation than in the control was observed. The different decay rates suggested a changed chemical environment around the radical. In comparison with the control, the levels of carotenoids and hydrophobic proteins in the thylakoids decreased, and the lipid/protein ratio increased after a mild water deficit. After moderate drought, the increased levels of hydrophilic proteins and carotenoids seem unsufficient to limit the improved capacity to leak electrons from the thylakoids. After a severe water stress, a decrease in unsaturation and in linolenic acid as well as a loss of lipolytic antioxidants took place, which may have rendered the thylakoids more sensiive to attack by activated forms of oxygen. The results suggest that during water deficit, the interactions among membrane components change in relation to a changed chemical composition. Such changes are probably among the causes for changes in the conformation of proteins and in the position of various molecular species in he lipid bilayer, so that they become more exposed to molecular oxygen
Plasma-membrane proteins in water-stressed sunflower seedlings
No full textIn sunflower seedlings either regularly watered or subjected to water stress by withholding water for 5 days, plasma membrane was isolated by partitioning in an aqueous polymer two-phase system. In the stressed seedlings an osmotic adjustment of 0.1 MPa took place. Water deficit conditions determined an increase in membrane permeability and in the recovery of plasma membrane proteins. Total and soluble protein levels decreased by 9.4 and 45.8% respectively in the stressed seedlings. The sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the soluble proteins and plama membrane proteins did not show qualitative changes in the protein patterns of both the control and the stressed seedlings. Several quantitative differences in the levels of plasma membrane proteins were observed: the 60, 56 and 37 KDa bands, as well as the 37 to 20.1 KDa group, reached higher levels under stress. These last polypeptides can be identified as peripheral plasma membrane proteins of the bilayer
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