Production of Nitric Oxide and Phosphatidic Acid is Involved in Activation of Plasma Membrane H+-ATPase in Maize Root Tips in Simulated Drought Stress

Nitric oxide (NO), phospholipase D (PLD) and plasma membrane (PM) H+-ATPase play crucial roles in plant response to drought stress, but the mechanisms of their function and their relationships in this process are still unclear. Here, we investigated how NO regulate PM H+-ATPase activity in maize (Zea mays L.) root tips in drought stress via inducing PLD-derived phosphatidic acid (PA) formation. Our results showed that drought stress stimulated NO production, up-regulated ZmPLD gene expression and stimulated PLD activity, coupled with PA production. With the elevation of PA content in a specific period (6 to 24 h after treatment), the PM H+-ATPase was stimulated. The NO scavenger impaired drought-induced PLD activation, PA formation and PM H+-ATPase activation at 12 h after treatment. The PLD inhibitor impaired drought-induced PA formation and PM H+-ATPase activation at 12 h after treatment. The NO scavenger, PLD inhibitor and PM H+-ATPase inhibitor aggravated the injury caused by drought stress. Exogenous NO alleviated the injury through a further elevation and a longer maintenance of ZmPLD gene expression, PLD activity, PA content and PM H+-ATPase activity in drought stress. The stimulation effect of exogenous NO on PA formation and PM H+-ATPase activation at 12 h after treatment were partly inhibited by the PLD inhibitor. The results suggested that as an early signal, NO triggers maize plant response to drought stress through increasing PM H+-ATPase activity in root tips. PLD-derived PA acts downstream of NO in this process.