Contrasting Roles of Reactive Oxygen Species in Pyrophosphate-Induced Growth Inhibition under Normal and Salt Stress Conditions

Pyrophosphate (PPi) is an important chemical raw material; however, little research has focus on the effects of exogenous PPi on plant growth, especially under salt stress condition. This study investigated the impact of sodium pyrophosphate (Na-PPi) on the growth of Arabidopsis under 0 mM and 50 mM NaCl conditions. The results showed that 1 mM Na-PPi significantly inhibited the growth of Arabidopsis seedlings in 0.5 MS medium and exacerbated the growth suppression caused by NaCl stress. Na-PPi significantly increased the accumulation of compatible osmolytes in Arabidopsis under NaCl treatment. Additionally, under normal growth condition, Na-PPi treatment significantly reduced the levels of ROS in Arabidopsis; however, this trend was reversed under salt stress condition. Meanwhile, Na-PPi was found to significantly enhance the activity of antioxidant enzymes under both normal and salt stress conditions. Under salt stress, Na-PPi induces the upregulation of genes related to oxidative stress and salt/osmotic stress (such as marker for oxidative stress response protein and OSM34). Moreover, we discovered that Na-PPi significantly downregulates the expression of HAK5, which may account for the significantly decrease in K+ content of Arabidopsis seedlings. Intriguingly, genetic evidence shows that SOS proteins play crucial role in the adaptation of Arabidopsis to NaCl + Na-PPi stress. These findings shed light on the role of PPi in plant growth and stress responses, which contributes to the appropriate management and disposal of PPi in practice.