## 4 Discussion
Both ROS- and NO-mediated adaptation to stress is brought about by these molecules acting as retrograde signals in the cells to affect the function of target proteins through redox or S-nitrosylation post-translational modifications [66]. The two major pathways of NO synthesis in the plants are (i) oxidative-oxidation of L-arginine by NOS-like enzyme and (ii) reductive-reduction of nitrate by nitrate reductase (NR). In the plants, measurement of NOS-like activity by employing NOS inhibitors like L-NAME have suggested the existence of arginine-dependent NO production pathway [67; 44]. Our analysis of the activity of both the enzymes showed a similar trend between NR activity and NO production in all the treatments except ST under non-saline and saline environments. On the other hand, NOS-like activity showed a higher reduction in relative values of magnetoprimed over unprimed in L-NAME treatment, but the corresponding reduction in NO content was comparatively less in this treatment. Higher reduction in NO content could be positively correlated with the reduced values of NR activity under ST treatment. The relative expression of the genes coding for NR and NOS-like activities confirmed and supported our results, as the gene _GmNR1_ recorded a higher (23.26 fold) abundance of transcripts in exogenous SNP in comparison to _GmNOS-like 2_ under the same treatment under saline conditions. Additionally, the results of the present study strengthen the conclusion of our previous study that confirmed the involvement of NR (through spectrophotometric and florescent microscopic dye) as the major contributor to NO production in magnetoprimed soybean seedlings exposed to salinity stress [15]. The preference of a reductive over an oxidative pathway in the germinating seeds may be the result of excess formation of NAD(P)H in respiration which increases during the germination process [68; 69]. Under chilling stress, the higher rate of respiration and ATP production stimulated the growth of seedlings obtained from primed rice seeds [69; 70]. In the reductive pathway, nitrate is reduced to nitrite by utilization of cytosolic NAD(P)H followed by its further reduction to NO by electron transfer from NAD(P)H to nitrite [71]. Magnetopriming and SNP supplementation both increased the _GmNOS-like 2_ and _GmNR1_ expression which supports the concomitant increment in NO production, although the transcript abundance of _GmNR1_ was more than that of _GmNOS-like 2_ gene. We also observed that ST, L-NAME and DPI caused the downregulation in gene expression of both _GmNOS-like 2_ and _GmNR1_ under both the conditions. However, the ST treatment caused the maximum reduction in _GmNR1_ transcript level as compared to L-NAME, which caused reduction in _GmNOS-like 2_ transcript levels in the present study. In plants, the NO/ROS regulate various metabolic processes through their control on the perception, metabolism or signal transduction of different hormones like ABA, auxins, gibberellin, cytokins and ethylene [72; 73]. NO governs the ABA signalling pathway at different steps involving the S-nitrosylation of PYR/PYL/RCAR complex or SUCROSE NON-FERMENTING (SNF)-RELATED PROTEIN KINASE2.6 (SnRK2) to inactivate them or cause proteasomal degradation of ABSCISIC ACID INSENSITIVE5 to break seed dormancy and promote germination [74]. Unlike ABA, GA is known to promote seed germination in various crops [30; 75; 76]. Therefore, in our previous study, we elucidated that ABA does not exclusively control the germination process, but the hormonal homeostasis under high ROS levels in magnetoprimed tomato seeds is managed by the ABA/GA ratio to enhance the rate of germination under unstressed conditions [48], which was also reported in the previous studies [30; 77; 78; 79]. We have also recorded a significant increase (301\(\%\)) in ABA content in UP seeds grown in saline conditions as compared to UP seeds of non-saline conditions.