## 4 Discussion  
A reduced percentage of germination and poor seedling growth in soybean under salinity is the combined outcome of cell water relation and specific ion toxicity [6; 46; 47]. Seed priming helps to activate the plant immune system through a network of signalling molecules, phytohormones and stress-responsive proteins that empower them to safeguard against abiotic and biotic stresses [15; 34; 48; 49]. Magnetopriming of seeds has been shown to effectively help the seeds to withstand stress effects during the germination process in various crops [9; 12; 14]. Previously, [PERSON] et al. [15] found that seed germination was enhanced by 23% via MP of soybean seeds under salt (50 mM NaCl) stress. Our study revealed that magnetopriming increased the stress tolerance index (STI) in the primed soybean seeds under 50 mM NaCl salinity. The improvement in STI with NO donor (SNP) and its loss with NO/ROS inhibitors ST, L-NAME and DPI in both unprimed and primed seeds indicated the direct involvement of NO along with ROS towards imparting salt tolerance. The negative effect of salinity on seed germination and plant growth was observed to be reduced by the external application of SNP in _Chenopodium_ and _Raphanus_[50; 51]. The salinity tolerance in plants is maintained by a low Na\({}^{+}\)/K\({}^{+}\) ratio [52] which is mainly disturbed by high cellular concentrations of Na\({}^{+}\)[53]. Magnetopriming restricted the influx of Na\({}^{+}\) in the germinating seeds, as the seedlings showed lower ratios under saline condition. Likewise, in an earlier study, magnetopriming of wheat seeds helped in maintaining a lower Na\({}^{+}\)/K\({}^{+}\) ratio under salinity [54]. When we treated the seeds with SNP it favoured a further reduction in both unprimed and primed seeds. In addition, the exogenous NO treatment improved salt tolerance by maintaining low levels of Na\({}^{+}\) in Jatropha seedlings [55] and enhanced production of ascorbate, glutathione, total phenolic content, proline and flavonoids in spinach [56] and tomato [57]. Also, the SNP pre-treatment significantly increased the K\({}^{+}\) and decreased Na\({}^{+}\) contents, consequentially increasing the level of K\({}^{+}\)/Na\({}^{+}\) ratio in _Brassica chinensis_ leading to improved germination and seedling growth under NaCl stress [24]. Molecular analysis of NO-treated plants growing under salt stress enhanced the expression of _SOS1_ and _NHX1_[58] and _H\({}^{+}\)-ATPase_ and _H\({}^{+}\)-PPase_[59] genes in the stressed leaves which were suggested to reduce Na accumulation and increase the activity of Na\({}^{+}\)/H\({}^{+}\) exchange in the tissues, respectively. Endogenous NO content increased in the magnetoprimed seeds in the absence or presence of NO donor, whereas NO inhibitors (ST and L-NAME) showed a reduction in content under both the non-saline and saline growing conditions. NO is a redox signalling molecule that controls various physiological processes in the plants such as germination, flowering, senescence and multiple stresses [2; 22]. Under stress conditions, external application of NO alleviates the plant by upregulating its antioxidant defence system and helping in ROS homeostasis [60; 61]. ROS homeostasis has been linked to an enhanced rate of germination and vigor in magnetoprimed seeds of soybean [62]. Amongst the various mechanisms involved in buffering the levels of ROS, NO is a proven candidate [63; 64]. In our experiments, the treatment with DPI (ROS inhibitor) showed low levels of NO, indicating that NO may not be required for the scavenging process as ROS production is inhibited. Thus, the ability of DPI to restrict the production of ROS as well as NO, and the inability of NO-modulators to prevent the rise in ROS levels, indicated that inhibition of ROS production controlled the synthesis of NO in the seedlings. Similarly, [PERSON] and [PERSON] [65] also found that DPI reduced the NO production along with ROS in _Agropyron cristatum_.