## 3 Results
### Physiological Parameters
The content of superoxide anion and MDA depended on the water stress level (PEG level) and various foliar sprays (Table S9). The superoxide anion and MDA levels of the analysed plant were found to have no significant effect on antioxidants like ascorbate, phenolic compounds, flavonoids, and Chl a and b contents, as evidenced by \(p\)-values (Table S10). A positive correlation was found between H\({}_{2}\)O\({}_{2}\) content and ascorbate, proline, phenolic compounds, and flavonoid contents. Moreover, the results were statistically significant (\(p<0.05\)). Moreover, a significant increase in the accumulation of proline (Pro) and ascorbic acid (AsA) was also recorded under drought stress. The application of exogenous acids significantly increased the accumulation of both Pro and AsA under stress and control conditions (Figure 2). The osmolyte accumulation (Pro) was higher under the stronger stress (7.5% PEG), in contrast to the AsA level, which was higher under 5% PGE. SA resulted in a greater increase between the three acid treatments than MA and CA. The AsA levels were, respectively, 1.8-fold (SA) and 1.5-fold (MA and CA) higher than in non-treated stress conditions. Positive correlations were found between proline content and the same fraction of the original (MA and CA). Figure 1: Effect of foliar application of salicylic acid (SA), maleic acid (MA), and citric acid (CA) on selected physiological parameters: (**A**) superoxide anion radical, (**B**) H\({}_{2}\)O\({}_{2}\), (**C**) MDA. Values with the same letter do not differ significantly at \(p\) 0.05.  
and all antioxidants (AsA, Phe, Fla, and Car) (Table S10). These results were statistically significant, as evidenced by \(p\) < 0.05. The content of Pro and AsA depended on the water stress level (PEG level) and various foliar sprays (Table S9). In addition, stress conditions significantly increased the pool of phenolic compounds (TFC), including flavonoids (Fla). The TPC and Fla levels were, respectively, 2.8-fold and 1.5-fold (in 5% PEG) and 4.5-fold and 2.0-fold (in 7.5% PEG) higher (Figure 3). Acid foliar spray significantly increased parameter content under both drought and control conditions. SA was most effective in increasing its contents, whereas CA was the least effective. In the plants sprayed with SA, the level of TPC increased three-fold at 5% PEG and twice at 7.5% PEG. Positive correlations were found between phenolic compounds and flavonoid content (Table S10). These results were statistically significant, as evidenced by \(p\) < 0.05. Positive correlations were also found between both Phe and Fla and superoxide anion, MDA, and total chlorophyll but were statistically insignificant (\(p\) > 0.05). The content of Phe and Fla depended on the water stress level (PEG level) and various foliar sprays (Table S9). Figure 2: Effect of foliar application of salicylic acid (SA), maleic acid (MA), and citric acid (CA) on selected physiological parameters: (**A**) ascorbic acid, (**B**) proline contents. Values with the same letter do not differ significantly at \(p\) 0.05. The chlorophyll a and b amounts did not change under all the applied experimental conditions (Figure 4). Their levels were insignificant. The total chlorophyll content was found to have no significant effect on the remaining analysed parameters, as evidenced by \(p\)-values (Table S10). The decrease in carotenoid levels was recorded under drought stress while applying exogenous acids, which significantly increased the accumulation. The content of carotenoids depended on the water stress level (PEG level) and various foliar sprays (Table S9). Opposite to Chl a + b, the correlation between carotenoids and all analysed parameters (except H2O2) was found. Figure 4: Effect of foliar application of salicylic acid (SA), maleic acid (MA), and citric acid (CA) on selected physiological parameters: (**A**) total chlorophyll, (**B**) carotenoid contents. Values with the same letter do not differ significantly at \(p\) 0.05.