## 3 Results and Discussions
### Secondary Experiments  
In Figure 4, the mycorrhizal frequency (F%) of lettuce, carrot, and pepper plants grown in VAs amended soil is given. Upon comparison with control, F% was affected the most by SDZ, followed by OTC antibiotics. The effect of STR antibiotics on F% of lettuce, carrot, and pepper plants was found not to be significantly different (\(p<0.05\)) from control. At minimum VAs dosage of 10 mg kg\({}^{-1}\), the frequency of mycorrhizal colonization was higher than that of control. As described in previous studies, under abiotic stress conditions, increased colonization of plant roots by AM fungi is observed [31; 32; 33]. An increase in F% at low concentrations followed a steady decline with the increasing dosage of VAs in the soil-mannure mix. The formation of mycorrhizal structures in root is associated with the effective colonization of root by various AMF species [31; 33]. Roots being the first plant organ to come in contact with the VAs, the physiology of the root affected by VAs treatment, thereby affected the intensity of mycorrhizal colonization. The observed F% varied depending on plant type indicating species variability. The F% of carrot, a root vegetable, reporting the highest accumulation of VAs was affected the most, followed by lettuce and then pepper.  
Figure 5 depicts the free proline content in the root and leaf tissues examined. In all three plants, we observed a variation in the accumulation of free proline in response to VAs stress. Free proline concentration increased with increasing abiotic stress (VAs concentration) and was the highest in carrot plants followed by lettuce and then pepper plants. The highest proline accumulation occurred at the highest VAs concentration of 100 mg kg\({}^{-1}\). As reported in a previous study, the accumulation of proline in _Medicago polymorpha_ and _Medicago ciliaris_ under NaCl stress, was the greatest at the highest NaCl concentration of 100 mM [34]. Proline contributes to osmotic adjustment, stabilization, and protection of membranes integrity and macromolecules from the damage as a ROS scavenger [35; 36]. It is significant in maintaining growth when plants are under stress [37]. Under unfavorable conditions, plants accumulate amino acid metabolites, a constituent of proteins, that play a significant role in plant development and metabolism. Among the amino acids, 'proline' has been reported to play a beneficial role in plants exposed to various stress conditions [38]. Proline plays three significant roles during stress, i.e., as a metal chelator, antioxidant molecule, and a signaling molecule. The high proline concentration in roots, in comparison to leaves, is likely due to the higher concentration of VAs in the roots. Previous studies have also reported an increase in proline accumulation in plants under stress [39].  
Figure 3: _Glutathione-s-transferase_ (GST) activity of lettuce, carrot and pepper grown in soil treated with VAs. Error bars represent standard error. Concentration values followed by different letters are significantly different (\(p<0.05\)) according to [PERSON]’s multiple range test. SDZ = Sulfadimethoxine; OTC = Oxytetracycline; STR = Streptomycin.  
Free proline content varied between the plant roots and leaves. Free proline content was higher in the root than in leaves, likely due to the higher accumulation of VAs in plant root. Another possibility is the direct exposure of the roots to the soil contaminated with VAs. The highest accumulation of free proline occurred in carrot roots at 100 mg kg\({}^{-1}\) SDZ (\(189.84\pm 7.23\) mg g\({}^{-1}\)).