Proline concentration in leaves was determined using the sulfosalicylic acid method described by Zheng et al. [20] (link), where 5 mL of reaction solution consisted of 1 mL of 3% sulfosalicylic acid leaf extract, 1 mL of glacial acetic acid, 1 mL of acidic ninhydrin reagent, and 2 mL of toluene. Hydrogen peroxide (H 2 O 2 ) levels in leaves were measured as per the protocol described by Velikova et al. [21] (link), where the reaction solution consisted of 1 mL of 0.1% trichloroacetic acid leaf extract, 1 mL of 10 mmol/L potassium phosphate buffer (pH 7.0), and 2 mL of 1 mol/L potassium iodide solution. Leaf soluble protein levels were analyzed by the Coomassie Brilliant Blue G250 staining method outlined by Bradford [22] (link).