Role of exogenous signaling molecules in alleviating salt-induced oxidative stress in rice (Oryza sativa L.): a comparative study

Intensified salt stress is an acute hindrance to crop cultivation, whereas plant signaling molecules can efficiently prompt salinity tolerance. Therefore, this study was accomplished to explore the potential salinity stress-mitigating effect of different signaling molecules in rice. The rice (cv. BRRI dhan29) seeds were immersed in 20 mM KNO3, 0.15 mM H2O2, 0.8 mM AsA (ascorbic acid) and 10 mM CaCl2 solutions for 24 h. Eventually, primed seeds were exposed to 75 mM NaCl in Petri dishes during germination. Moreover, 14-day-old rice seedlings were pretreated with different agents, viz., KNO3, H2O2, AsA and CaCl2 (concentrations were same as previous), for 2 days. Primed and non-primed seedlings were grown for 4 days under 75 mM NaCl stress condition. The result revealed that salt stress caused reduced germination indices and pre-seedling and seedling growth inhibition and impaired photosynthetic capacity, whereas catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) activities were decreased in salt-treated plants. However, application of the four signaling molecules promoted the germination indices and growth and resisted chlorosis. Pretreatment with CaCl2 and AsA was observed to be relatively more efficient in conferring salinity tolerance of rice as reflected from the significant enhanced germination and growth in the saline medium by increasing reactive oxygen species (ROS) scavenging capacity, both at germination and seedling stage. All the selected signaling molecules significantly detoxified excess ROS, i.e., H2O2 and \({\text{O}}_{2}^{ \cdot - }\) and reduced lipid peroxidation by up-regulating the enzymes, CAT, APX and POX. Moreover, H2O2 and KNO3 pretreatment also mitigated salt-imposed oxidative stress and enhanced growth performance of rice seedlings. Overall, the study confirms that CaCl2 and AsA pretreatment were more effective than H2O2 and KNO3 priming to improve salt tolerance in rice.