Polyamines increase nitric oxide and reactive oxygen species in guard cells of Arabidopsis thaliana during stomatal closure

A comprehensive study which was undertaken on the effect of three polyamines (PAs) on stomatal closure was examined in relation to nitric oxide (NO) and reactive oxygen species (ROS) levels in guard cells of Arabidopsis thaliana. Three PAs—putrescine (Put), spermidine (Spd), and spermine (Spm)—induced stomatal closure, while increasing the levels of NO as well as ROS in guard cells. The roles of NO and ROS were confirmed by the reversal of closure by cPTIO (NO scavenger) and catalase (ROS scavenger). The presence of L-NAME (NOS-like enzyme inhibitor) reversed PA-induced stomatal closure, suggesting that NOS-like enzyme played a significant role in NO production during stomatal closure. The reversal of stomatal closure by diphenylene iodonium (DPI, NADPH oxidase inhibitor) or 2-bromoethylamine (BEA, copper amine oxidase inhibitor) or 1,12 diaminododecane (DADD, polyamine oxidase inhibitor) was partial. In contrast, the presence of DPI along with BEA/DADD reversed completely the closure by PAs. We conclude that both NO and ROS are essential signaling components during Put-, Spd-, and Spm-induced stomatal closure. The PA-induced ROS production is mediated by both NADPH oxidase and amine oxidase. The rise in ROS appears to be upstream of NO. Ours is the first detailed study on the role of NO and its dependence on ROS during stomatal closure by three major PAs.