Interaction between hydrogen peroxide and sodium nitroprusside following chemical priming of Ocimum basilicum L. against salt stress

Sodium nitroprusside (SNP) and hydrogen peroxide (H₂O₂)_, as priming agents, have the well-recorded property to increase plant tolerance against a range of different abiotic stresses such as salinity. In this regard, the present study was conducted to evaluate the effect of different levels of SNP (100 and 200 µM) and H₂O₂ (2.5 and 5 mM) as well as their combinations under salt stress (0 and 50 mM NaCl) on key physiological and biochemical attributes of the economically important aromatic plant basil (Ocimum basilicum L.) grown under hydroponic culture. Results revealed that morphological parameters such as plant height, root length, leaf fresh and dry weights (FW and DW) were significantly decreased by salinity stress, while SNP and H₂O₂ treatments, alone or combined, increased FW and DW thus enhancing plant tolerance to salt stress. Furthermore, 200 µM SNP + 2.5 mM H₂O₂ appeared to be the most effective treatment by causing significant increase in chlorophyll a and b, anthocyanin content and guaiacol peroxidase and ascorbate peroxidase enzymes activities under saline condition. In addition, analytical measurements showed that essential oil profile (concentration of main components) under salt stress was mostly affected by SNP and H₂O₂ treatments. The highest increase was observed for methyl chavicol (43.09–69.91%), linalool (4.8–17.9%), cadinol (1.5–3.2%) and epi-α-cadinol (0.18–10.75%) compounds. In conclusion, current findings demonstrated a positive crosstalk between SNP and H₂O₂ toward improved basil plant tolerance to salt stress, linked with regulation of essential oil composition.