Phytometrics Co., Ltd. 1 article published in JoVE Immunology and Infection Direct Observation and Automated Measurement of Stomatal Responses to Pseudomonas syringae pv. tomato DC3000 in Arabidopsis thaliana Rikako Hirata*1, Momoko Takagi*2, Yosuke Toda2,3, Akira Mine1 1Graduate School of Agriculture, Kyoto University, 2Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, 3Phytometrics Co., Ltd. Here, we present a simple method for direct observation and automated measurement of stomatal responses to bacterial invasion in Arabidopsis thaliana. This method leverages a portable stomatal imaging device, together with an image analysis pipeline designed for leaf images captured by the device.