## 4 Discussion
In our studies, Cd concentration in _Brassica juncea_ (L.) root was significantly increased under Cd-stress that was reduced due to inoculation with Cd-tolerant PGPR strains. This might be due to EPS and IAA-producing ability of these PGPR strains. It has been well documented that cadmium-tolerant PGPR strains help to reduce Cd uptake by crop plants by stabilizing it in the soil through production of exopolysaccharides [27]. For example, Siripromadulsil and Siripromadulsil [69] reported the reduced uptake and accumulation of Cd in rice grains. The reduction in Cd uptake due to phytostabilization of heavy metals by using EPS, and IAA-producing bacterial strains has also been reported by [PERSON] et al. [85]. Recently, [PERSON] et al. [35] reported that Cd-tolerant PGPR helped in the immobilization of Cd in soil thus reducing their uptake due to enhanced sequestration of Cd in soil by producing phytohormones, siderophores and polymeric substances. Although, inoculation with PGPR may enhance the uptake of heavy metals in plants [33], the phytostabilization of heavy metals is also an effective strategy to reduce Cd uptake by growing plants [34]. In another study, [PERSON] et al. [29] reported that rhizbacterial strains belonging to the genera _Serratia_, _Bacillus_, _Stenotropomonas_, and _Klebsiella_ improved growth of crop plants due to decrease in Cd-uptake. They attributed these positive effects to IAA production ability of Cd-tolerant PGPR strains. The increased biomass production due to the decrease in Cd uptake in maize after inoculation with PGPR strains under stress has also been reported by [PERSON] et al. [86]. In our studies, _Brassica juncea_ (L.) plants exposed to Cd-stress showed higher the production of antioxidants (SOD, POX and CAT) that is a defense mechanism used by crop plants exposed to osmotic stress [87]. Enhanced activities of antioxidant enzymes have also been reported in previous studies [80]. The SOD scavenges and catalyzes the ROS specie superoxide and converts it in to H\({}_{2}\)O\({}_{2}\) and molecular oxygen under stressed soil environments [88]. The H\({}_{2}\)O\({}_{2}\) is also an intermediate ROS which is toxic to plants. This H\({}_{2}\)O\({}_{2}\) is converted into water and oxygen by other antioxidant enzymes i.e., CAT and POX [89]. Previous studies also report the enhanced activities of POX and CAT in plants under Cd-stress [18; 90] while SOD activity showed variable behavior under different studies. The increased activity of SOD has been reported in _Brassica juncea_[80] while other studies report the decrease in SOD activities in plants under Cd-stress [91]. The heavy metal tolerant PGPR with metal immobilizing ability have been well documented to enhance plant growth, physiology, and antioxidant status by reducing the metal bioavailability and accumulation in plant tissues [91; 92]. Several PGPR strains have been documented to reduce the negative effects of ROS produced under stress [16; 32; 79] through enzymatic antioxidants. Enhanced CAT activity in crop plants due to inoculation with Cd-tolerant PGPR under Cd-stress has also been reported in previous studies [15; 93]. A positive impact of inoculation with _Klebsiella pneumoniae_ strain K5 on activities of SOD, and CAT has also been reported by [PERSON] et al. [25]. [PERSON] et al. [94; 95] reported the effectiveness of _Sphingomonas_ SaMR12 to alleviate Cd-stress in rapeseed by regulating the Reduced glutathione (GSH)-AsA cycle through activities of antioxidant enzyme systems. In our study, the strain FN13 showed significantly better results than other two strains in improving the growth, physiology, and antioxidants status of _Brassica juncea_ (L.) plants that might be due to better survival efficacy of the strain FN13 under Cd-stress. This might also be due to better PGP traits such as siderophore production, IAA production and EPS production of the strain FN13 as reported by [PERSON] [14].