Sodic alkaline stress mitigation by interaction of nitric oxide and polyamines involves antioxidants and physiological strategies in Solanum lycopersicum

Nitric oxide (NO) and polyamines (PAs) are two kinds of important signal in mediating plant tolerance to abiotic stress. In this study, we observed that both NO and PAs decreased alkaline stress in tomato plants, which may be a result of their role in regulating nutrient balance and reactive oxygen species (ROS), thereby protecting the photosynthetic system from damage. Further investigation indicated that NO and PAs induced accumulation of each other. Furthermore, the function of PAs could be removed by a NO scavenger, cPTIO. On the other hand, application of MGBG, a PA synthesis inhibitor, did little to abolish the function of NO. To further elucidate the mechanism by which NO and PAs alleviate alkaline stress, the expression of several genes associated with abiotic stress was analyzed by qRT-PCR. NO and PAs significantly upregulated ion transporters such as the plasma membrane Na+/H+ antiporter (SlSOS1), vacuolar Na+/H+ exchanger (SlNHX1 and SlNHX2), and Na+ transporter and signal components including ROS, MAPK, and Ca2+ signal pathways, as well as several transcription factors. All of these play important roles in plant adaptation to stress conditions.