## 2 Enzymatic Defensive Mechanisms
### Catalase
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Plant Species** & **Common Name** & **Genomic DNA or** & **Subcellular Localisation and Site of** & **References** \\ \hline _Nicotiana_ & & & **Protein** & **Detection in Plant** & **References** \\ _plumbagino/olia_ & Tex-Mex tobacco & CAT\({}_{1}\)–CAT\({}_{3}\) & Peroxisomes in leaves & [84] \\ _Arabidopsis_ & & & & \\ _thaliana_ & Arabidopsis & CAT\({}_{1}\)–CAT\({}_{3}\) & (CAT\({}_{1}\), CAT\({}_{2}\)), in pollen and seeds (CAT\({}_{1}\)), & [81; 98; 99; 100; 101] \\ \hline _Cucurpita pepo_ & Pumpkin & CAT\({}_{1}\)–CAT\({}_{3}\) & (C\({}_{1}\)), mature leaves, stem (CAT\({}_{2}\)), green cotyledons and green hypocotyls (CAT\({}_{2}\), CAT\({}_{3}\)), and roots (CAT\({}_{3}\)) & [82] \\ \hline _Glycine max_ & Soybean & CAT\({}_{1}\)–CAT\({}_{3}\) & Glycos in developing kernels (CAT\({}_{1}\)), green leaves (CAT\({}_{2}\), CAT\({}_{3}\)), roots (CAT\({}_{3}\)), and epicotyl of the developing seedlings (CAT\({}_{3}\)) & [102] \\ \hline _Zea mays_ & Maize & CAT\({}_{1}\)–CAT\({}_{3}\) & In scutella, milky endosperm of immature kernels, leaves and epicotyls (CAT\({}_{1}\)); Post-germinative scutella, with lower levels in leaves, epicotyls and growing kernels (CAT\({}_{2}\)); Epicotyls and, to a lesser extent, in leaves and scutella (CAT\({}_{3}\)) & [83; 103; 104; 105; 106; 107] \\ \hline _Capsicum annuum_ & Hot pepper & CAT\({}_{1}\)–CAT\({}_{3}\) & Peroxisomes in leaf and stem & [108] \\ \hline _Nicotiana tabacum_ & Tobacco & CAT\({}_{1}\)–CAT\({}_{3}\) & Peroxisomes in leaves & [109; 110] \\ \hline _Ricinus cannunuis_ & Castor bean & CAT\({}_{1}\), CAT\({}_{2}\) & Glycosomes, peroxisomes in hypocotyls and cotyledons (CAT\({}_{1}\)) & [88; 111] \\ \hline _Hurdeom vulgare_ & Barley & CAT\({}_{1}\), CAT\({}_{2}\) & Peroxisomes in whole endosperms, in isolated aleurones and in developing seeds (CAT\({}_{1}\)), in etiolated seedling shoots and leaf blades (CAT\({}_{2}\)) & [85] \\ \hline _Tritcium aestivum_ & Wheat & CAT\({}_{1}\), CAT\({}_{2}\) & Peroxisomes in leaves & [112] \\ \hline _Solanum_ & Potato & CAT\({}_{1}\), CAT\({}_{2}\) & Peroxisomes in leaves & [113; 114] \\ _tubrosum_ & Tomato & CAT\({}_{1}\), CAT\({}_{2}\) & Peroxisomes in leaves & [86; 115; 116] \\ \hline _Lycopersicum_ & Tomato & CAT\({}_{1}\), CAT\({}_{2}\) & Peroxisomes in leaves & [86; 115; 116] \\ _scutelum_ & & & & \\ \hline _Nicotiana sylvestris_ & Woodland & CAT\({}_{1}\), CAT\({}_{4}\) & Peroxisomes in leaves & [117] \\ \hline _Vigna radiata_ & Mung bean & CAT\({}_{1}\) & Glyoxysomes, leaf peroxisomes, and nonspecialised microbodies (etiolated or nongreen tissues) & [118] \\ \hline _Scale cereale_ & Rye & CAT\({}_{1}\) & Peroxisomes in leaves & [119] \\ \hline _Ipomoa buttatas_ & Sweet potato & CAT\({}_{1}\) & Peroxisomes in leaves & [87; 120] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Because of low affinity of CATs to H\({}_{2}\)O\({}_{2}\), only high concentrations of H\({}_{2}\)O\({}_{2}\) have the possibility of being eliminated by CATs [126]. In particular, CAT\({}_{1}\) is responsible for scavenging H\({}_{2}\)O\({}_{2}\) under abiotic stress conditions, and CAT\({}_{2}\) and CAT\({}_{3}\) for removing H\({}_{2}\)O\({}_{2}\) to maintain ROS homeostasis both in light and darkness [78]. Stimulation of enzymatic antioxidants such as CATs has been reported in maize plants exposed to arsenate and arsenite [127]. Leaf senescence significantly impacts the concentration reduction of CAT\({}_{2}\) rather than CAT\({}_{1}\) in tobacco [110]. As for the model plant, _Arabidopsis_, all three CATs are engaged with photooxidation responses [128; 11; 124], CAT\({}_{1}\) is involved in the plant's response to drought and salt stress [129], CAT\({}_{2}\) is implicated in toxic metal [130], heat [131], cold and salt [132] stress responses and CAT\({}_{3}\) is incorporated in drought stress responses [133].