Abstract
The protective ability of α-tocopherol (TOH) and gallic acid (GA) acting simultaneously at the moment of oxidizer application was evaluated by determination of galactolipid layers’ oxidation degree. Addition of GA resulted in a significant decrease of ozone-derived radicals shifting the threshold of lipid sensitivity by an amount approximately corresponding to the GA intake in bulk reaction with ozone. TOH presence in lipid layers results in a change of the role of GA which additionally may be involved in the reduction of tocopheroxyl radical formed during oxidation. This leads to a decrease in effectiveness of GA in diminishing the amount of ozone radicals. Such an effect was not observed for mixed layers containing galactolipid and pre-oxidized tocopherol where the ozone threshold level was associated with a stoichiometry of GA + O3 reaction. It was concluded that probably subsequent transformations of tocopheroxyl radical to less reactive forms prevent its reaction with GA the entire quantity of which is used for radicals scavenging. This result shows the role of time parameter in systems where substrates are engaged in various reactions taking place simultaneously. The inactivation of 1,1-diphenyl-2-picrylhydrazyl radical by studied antioxidants in homogeneous system confirmed observations made on the basis of lipid layer properties indicating their antagonistic action (at least at studied conditions). Formation of layers in post-oxidation situation did not depend whether tocopherol was oxidized during oxidation of lipid/tocopherol mixture or was introduced as pre-oxidized. This may be interpreted as indication that products of tocopherol oxidation may stabilize lipid layers.
Highlights
Environmental stress causes an increase in the concentrations of reactive oxygen species (ROS) in the cell
Similar diminishing of ozone concentration range where galactolipids are effectively oxidized was found for mixed tocopherol/galactolipid layers at higher gallic acid (GA) content (Fig. 4; Table 1)
This decrease was especially distinct for MGDG/tocopherol mixture reaching about 30 %
Summary
Environmental stress (drought, salinity, low/high temperature, excess of light) causes an increase in the concentrations of reactive oxygen species (ROS) in the cell. Shortterm or chronic presence of ROS excess is called oxidative stress, and its existence can lead to serious damage or death of cells. Lipids building the cell membranes constitute the first target for ROS whose action leads to the disturbances or loss of membrane functions. Peroxidation-induced changes in lipid composition result in the alteration of mechanical properties of membranes which in turn can disrupt the arrangement of the individual components (disorder of the membrane proteins), influence ion transport (gated ion channels), and modify selectivity and permeability of membranes (Frankel 2005). Defense reaction to stress is the synthesis of antioxidants whose quantity significantly increases and their uneven distribution can lead to locally high concentrations. Multiple literature data confirm rise in an amount of both hydrophilic (Grenet al. 2012; Łabanowska et al 2012; Grzesiak et al 2013; Marcinska et al 2013; Barbasz et al 2015) and hydrophobic
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