Guard cell photosynthesis is crucial in abscisic acid‐induced stomatal closure

Reactive oxygen species ( ROS ) are ubiquitous signaling molecules involved in diverse physiological processes, including stomatal closure. Photosynthetic electron transport ( PET ) is the main source of ROS generation in plants, but whether it functions in guard cell signaling remains unclear. Here, we assessed whether PET functions in abscisic acid ( ABA ) signaling in guard cells. ABA ‐elicited ROS were localized to guard cell chloroplasts in Arabidopsis thaliana , Commelina benghalensis , and Vicia faba in the light and abolished by the PET inhibitors 3‐(3, 4‐dichlorophenyl)‐1, 1‐dimethylurea and 2, 5‐dibromo‐3‐methyl‐6‐isopropyl‐ p ‐benzoquinone. These inhibitors reduced ABA ‐induced stomatal closure in all three species, as well as in the NADPH oxidase‐lacking mutant atrboh D/F . However, an NADPH oxidase inhibitor did not fully eliminate ABA ‐induced ROS in the chloroplasts, and ABA ‐induced ROS were still observed in the guard cell chloroplasts of atrboh D/F . This study demonstrates that ROS generated through PET act as signaling molecules in ABA ‐induced stomatal closure and that this occurs in concert with ROS derived through NADPH oxidase.