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Melatonin (Mel) and hydrogen sulphide (H2S) have emerged as potential regulators of plant metabolism during abiotic stress. Presence of excess NaCl in the soil is one of the main causes of reduced crop productivity worldwide. The present investigation examines the role of exogenous Mel and endogenous H2S in tomato seedlings grown under NaCl stress. Effect of 30 µm Mel on endogenous synthesis of H2S was examined in roots of NaCl‐stressed (200 mm) tomato seedlings. Also, the impact of treatments on the oxidative stress markers, transport of K+ and Na+, and activity of H+‐ATPase and antioxidant enzymes was assessed. Results show that NaCl‐stressed seedlings supplemented with 30 µm Mel had increased levels of endogenous H2S through enhanced L‐cysteine desulfhydrase activity. Mel in association with H2S overcame the deleterious effect of NaCl and induced retention of K+ that maintained a higher K+/Na+ ratio. Use of plasma membrane inhibitors and an H2S scavenger revealed that Mel‐induced regulation of K+/Na+ homeostasis in NaCl‐stressed seedling roots operates through endogenous H2S signalling. Synergistic effects of Mel and H2S also reduced the generation of ROS and oxidative destruction through the enhanced activity of antioxidant enzymes. Thus, it is suggested that the protective function of Mel against NaCl stress operates through an endogenous H2S‐dependent pathway, wherein H+‐ATPase‐energized secondary active transport regulates K+/Na+ homeostasis.

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The ability of microorganisms to generate resistance outcompetes with the generation of new and efficient antibiotics. Therefore, it is critically required to develop novel antibiotic agents and treatments to control bacterial infections. Green synthesized metallic and metal oxide nanoparticles are considered as the potential means to target bacteria as an alternative to antibiotics. Nanoconjugates have also attracted attention because of their increased biological activity as compared to free antibiotics. In the present investigation, silver nanoparticles (AgNPs), zinc oxide nanoparticles (ZnO NPs), copper oxide nanoparticles (CuO NPs), and iron oxide nanoparticles (FeO NPs) have been synthesized by using leaf extract of Ricinus communis. Characterization of nanoparticles was done by using UV–Vis Spectroscopy, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Energy Dispersive X-Ray Analyzer, X-ray Diffraction Analysis, and Dynamic Light Scattering Particle Size Analyzer. Interestingly, Streptomycin when combined with AgNPs, ZnO NPs, CuO NPs, and FeO NPs showed enhanced antibacterial activity against clinical isolates of S. aureus which suggested synergism between the nanoparticles and antibiotics. The highest enhanced antibacterial potential of Streptomycin was observed in conjugation with ZnO NPs (11 ± 0.5 mm) against S. aureus. Minimum inhibitory concentration of conjugates of AgNPs, ZnO NPs, CuO NPs, and FeO NPs with streptomycin against S. aureus was found to be 3.12, 2.5,10, and 12.5 μg/mL respectively. The considerable point of the present investigation is that S. aureus, which was resistant to streptomycin becomes highly susceptible to the same antibiotic when combined with nanoparticles. This particular observation opens up windows to mitigate the current crisis due to antibiotic resistance to combat antimicrobial infections efficiently.