What is the reason for the activation of the antioxidant system but the downregulation of lipid peroxidation products such as malondialdehyde (MDA), and is it a disorder of lipid metabolism?
The oxidative stress response is probably being induced at an earlier timepoint and by remaining upregulated is managing to metabolize more ROS than the control so there is less lipid oxidation occurring.
During oxidative stress, plants have evolved sophisticated defense mechanisms. Harmful reactive oxygen species (ROS) will be generated due to this plant enhancing its antioxidant defense system like increased activities of enzymatic antioxidants or non-enzymatic antioxidant molecules. As we know malondialdehyde (MDA) is a byproduct of lipid peroxidation. Thus more amount of ROS directly correlated with less lipid peroxidation reaction which may lead to less amount of malondialdehyde.
Many at times activation of the antioxidant system hinders the accumulation of free radical species which leads to peroxidation of macromolecules in the living system such LPO, protein carbonyl content increase.
Suppression of peroxidation is already a consequence, not a cause. The reasons for activation are diverse.
Following the oxidative stress, the trascripional factor Nrf2 was activate (sensor cysteines were modified by ROS), translocate to the nucleus and binds to the antioxidant response element (ARE), to activate genes expression for antioxidant enzymes SOD, CAT.
You will find more details in this publicationArticle NRF2 plays a critical role in mitigating lipid peroxidation ...
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