Fig. 4

Changes in the activities of SOD (A) and CAT (B) in iceberg lettuce plants caused by treatment with different concentrations of putrescine and the chitosan–putrescine nanocomposite (Put 1 mM–1 mM putrescine; Ch–Put 1 mM–1 mM chitosan–putrescine nanocomposite; Put 2.5 mM–2.5 mM putrescine; Ch–Put 2.5 mM–2.5 mM chitosan–putrescine nanocomposite; deionized water served as a control—Control) at two temperatures (4 °C and 20 °C). Different letters next to a particular parameter indicate significant differences according to Fisher’s LSD test (p ≤ 0.05). The values presented here are the means ± SEs (n = 3).