## 3 Results and Discussion
### Stress Induces Changes in the Redox State of _A. yydowii_
Bars with the asterisks (*) indicate the significant difference (**\(p<0.01\), * \(p<0.05\)) between the control and its respective treated samples. Analyzed by a two-way ANOVA with [PERSON]’s multiple comparisons test. oxidative markers and antioxidants were evaluated after 30 min, 2, and 8 h (some time points were the same for the evaluation of compatible solutes and Hog phosphorylation). SOD activity and GSH content were similar when _A. sydowii_ was growing without salt or with 0.5 M NaCl (time 0) and those levels were maintained when both conditions were shifted to 2.0 M NaCl. The levels of these antioxidant mechanisms were higher only when the fungus was growing in 2.0 M and they were maintained after shifting to media without salt or with 0.5 M NaCl. Hydroperoxides were not detected at the initial time in any condition, possibly because the fungus was already adapted to the growing media, while their levels increased mainly when _A. sydowii_ was shifted to 2.0 M NaCl. These results correlate with PAOP levels, where noticeable changes were observed when the fungus was shifted from a media without salt or 0.5 M NaCl to media with 2.0 M NaCl. There was also an increase in PAOP levels in other conditions, but only after 8 h. After osmotic shock, hydroperoxide was detected at 30 min of the exposure to a new environment only when the starter culture was growing in 2.0 M NaCl. The hydroperoxide was also detected when the starter culture growing in 0.5 M salt was transferred to the hypersaline condition (2.0 M NaCl). Accordingly, protein oxidation was detected after 30 min of exposition to the hypocenter hypersaline media, while MDA levels had an inverse correlation with SOD activity and the GSH levels. When cells growing in the absence of salt were exposed to either 0.5 M or 2.0 M NaCl, they responded with a decrease in the enzymatic (SOD) and non-enzymatic (GSH) antioxidant mechanisms. Strikingly when the cells were exposed to the optimal Na+ condition, there was no accumulation of peroxide or oxidized protein. However, there was an increase in lipid peroxidation. In the conditions where the fungus was shifted to a higher salinity (2.0 M), there was more lipid peroxidation; however, this might be due to lipoxygenase (LOXs) activity, which is regulated by abiotic stresses, including high salinity [137], rather than to an unregulated accumulation of ROS. Under this condition, the fungal response was to maintain SOD activity with lower amounts of GSH (around 90 \(\upmu\)g/mL). Previously, whether measurements of antioxidant cellular systems are proper indicators of stress tolerance has been discussed [138]. The effect of oxidative stress can depend on the duplication rate of the fungus and other environmental conditions. The presence of antioxidant mechanisms is a positive indicator of cell's tolerance to salinity [139]. ROS are not only indicators of stress, but also play regulatory roles depending on the cellular concentration. In plants, it has been proved that the expression of some LOXs is regulated by biotic and abiotic stresses including salinity and drought [137] and it is well known that ROS participate as signaling transduction molecules that control several pathways involved in the acclimation of these organisms to stressful conditions [140]. Figure 9: Oxidative stress and antioxidant markers evaluated in _A. ydowii_ after osmotic shock. Superoxide dismutase (SOD) and glutathione (GSH) (antioxidants markers, green in the heat maps), malondialdehydedehyde (MDA) and protein advance oxidation products (PAOP) (oxidative damage markers, red in the heat maps) were analyzed. Columns represents the average of at least three replicates, and bars represent the standard deviation. Details of statistical differences are shown in Supplementary Table S7.