Stomata in a state of emergency: H2O2 is the target locked

Stomatal movements are essential for plants to regulate photosynthesis rate, water status, and immunity. Upon stress stimulation, the production of hydrogen peroxide (H₂O₂) in the apoplasts and its accumulation within the guard cells are among key determinatives for stomatal closure. The regulatory mechanisms of H₂O₂ production and transport under plant–pathogen interaction and drought stress response in stomata are important fields of research. Specifically, the regulation of NADPH oxidases and aquaporins appears to be crucial in H₂O₂-controlled stomatal closure. In this review, we summarize how the calcium-dependent and calcium-independent mechanisms activate RESPIRATORY BURST OXIDASE HOMOLOG (RBOH)D/F NADPH oxidases and the aquaporin PIP2;1 to induce stomatal closure, and highlight how the H₂O₂ production is targeted by pathogen toxins and effectors to counteract plant immunity.