RESUMO
Posidonia oceanica is an endemic marine phanerogam of the Mediterranean Sea for that is very sensitive to the environmental changes, especially those related to human activities. The aim of this study was to evaluate the oxidative stress status of P. oceanica meadows exposed to spillage of hypersaline water from a desalination station by using biomarkers. Leaf samples of P. oceanica were obtained from 4 different points exposed to different levels of salinity water. Samples from the area with the highest salinity conditions were 75% shorter than the samples from the control area. Exposure to high salinity induced an increase in the levels of oxidative stress markers (malondialdehyde (MDA) and protein carbonyls). Interestingly, in the area with the highest salinity the activities of glutathione peroxidase, glutathione reductase and glutathione-s-transferase were significantly induced respect to the other studies areas, while catalase (CAT) and superoxide dismutase (SOD) activities were lower. In addition, salinity induced a progressive increase in non-enzymatic antioxidants (polyphenols and glutathione) and in total antioxidant capacity reaching the highest concentrations in samples directly affected by the saline discharge. In conclusion chronic exposure to high salinity induced an increase in total antioxidant capacity in P. oceanica. However, this increase was not enough to protect the plant against oxidative stress as it is evidenced by the raise in oxidative stress markers. The obtained data suggest that high salinity conditions deactivated CAT and SOD antioxidant enzymes and caused an increase in non-enzymatic antioxidants (polyphenols and glutathione) and in glutathione-related enzymes.