PtrWRKY75 promotes SA-induced stomatal closure by ROS production
Recent evidence indicates that SA induces accumulation of ROS and influences stomatal closure in Arabidopsis (Borsani et al. , 2001; Ullah et al. , 2018). To explore the function ofPtrWRKY75 in Populus , we measured ROS levels in the OE lines and WT plants. The OE lines and WT were treated with 0 or 0.5 mM SA for 0, 0.5, 1, 2, or 3 h, then their leaves were stained with 3,3′-diaminobenzidine (DAB). Hydrogen peroxide (H2O2) was visualized as a deep brown product resulting from the reaction of DAB with H2O2. The leaves of the OE lines were stained a deeper brown color than that of WT leaves under all conditions (Figure 2A). Thus, exogenous SA treatment increased the ROS content in the leaf to higher levels in the OE lines than in WT.
To investigate whether PtrWRKY75 promotes SA-induced stomatal closure in the OE lines and WT, leaf stomatal movement was observed under a scanning electron microscope. After treatment with exogenous SA for 1 h and 2 h, the stomata closed more rapidly in OE lines than in WT (Figure 2B). The stomatal aperture was much smaller in OE lines than in WT under exogenous SA treatment (Figure 2C). These results suggested that PtrWRKY75 promotes SA-induced stomatal closure via ROS production.