## 4 Plant-Bacteria Interaction Regulates Plant Protein and Metabolites Production
### Bacteria-Mediated Plant Metabolite Biosynthesis for Salt Stress Mitigation (Indirect Mechanism)
#### 4.2.3. Antioxidant Property in Plant  
Increased salinity causes the generation of reactive oxygen species (ROS) such as superoxide radical (O2'), hydroxyl radical (OH'), and hydrogen peroxide (H2O2) in plants [69]. The primary cause of ROS generation is the over-reduction of photosynthetic electrons caused by decreased photosynthetic activity [70]. Enzymatic antioxidants such as catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and non-enzymatic antioxidants such as flavonoids, carotenoids, glutathione, and tocopheroids are involved in the detoxification of ROS compounds [71] (Figure 3). Most of the non-enzymatic antioxidants are produced in the secondary metabolic processes [72]. The CAT and APX enzymes detoxify hydrogen peroxide by converting hydrogen peroxide (H2O2) to H2O and O2, and they are essential for ROS detoxification. When compared to salt-stressed soybean plants, peroxidase (POD) and polyphenol oxidase (PPO) concentra  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Crop** & **Salinity** & **Microorganism** & **Metabolites/Process** & **Gene** & **Impact on Plant** & **Reference** \\  & **Level** & **Used** & **Involved** & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._tions were considerably increased in _Bacillusaryabhattai_ ALT29 and _Arthobacter voluuveensis_ ALT43-inoculated soybean plants (21-68%) [40].  
The antioxidant enzyme system was discovered to be increased in _Paenibacillus yongiensis_ DCY84 treated _Panax ginseng_ plant grown in 300 mM salt concentration compared to control plants [60]. Ascorbate peroxidase 2 is an enzyme that converts the reactive oxygen species H2O2 to H2O via ascorbate oxidation [73]. Inoculation of _Burkholderia phytofirmans_ PsJN in _Arabidopsis thaliana_ enhanced the accumulation of the ascorbate peroxidase 2 enzyme at 250 mM of salt stress [64]. Similarly, inoculation of _Enterobacter_ sp. EJ01 was found to increase the ascorbate peroxidase enzyme in tomato plants in order to mitigate salt stress [53]. Another study found that employing _Bacillus firmus_ SW5 improved the activity of antioxidant enzymes (APX, CAT, SOD, and POD) in soybeans by up to 48% [52]. Their findings revealed that during salt stress, _Bacillus firmus_ SW5 elevated the antioxidant synthesizing genes up to three times more than control plants. _Koccuria rhizophila_ 14 asp inoculated plants exposed to salinity have stronger antioxidant (SOD and CAT) activities that increased as the salt concentration increases compared to uninoculated plants [59]. _Nocardioides_ sp. NIMMe6 and a phytohormone-rich bacterial culture filtrate extract in wheat plants up-regulated the genes involved in CAT, Mn-dependent superoxide dismutase (MnSOD), POD, and APX enzyme synthesis under salt stress condition [46]. According to [PERSON] et al. [61], the application of _Serratia liquefaciens_ KM4 reduces maize salt stress by up-regulating genes involved in the synthesis of antioxidant enzymes. By inducing the accumulation of antioxidant enzymes (ascorbate peroxidase, superoxide dismutase,  
Figure 3: Bacterial mediated plant processes for reducing salt stress, thereby boosting plant growth and development. Rhizosphere and phyllosphere bacteria involved in stress mitigation. Compounds in bold and underlined (pink colored) are up-regulated during plant-bacteria interactions in salt stress mitigation. TCA cycle (tricarboxylic acid cycle); ETC (electron transport chain); IAA (indole acetic acid); ABA (abscisic acid); CAT (catalase); SOD (superoxide dismutase); APX (ascorbate peroxidase); POD (peroxidase); VOCs (volatile organic compounds); SOS (salt overly sensitive).  
and catalase), our psychrotolerant _Pseudomonas frederiksbergensis_ OS261 strain reduced salt stress in red pepper plants [74].