The plant plasma membrane (PM) is highly dynamic and PM proteins play important roles in regulating various transport processes.Measuring the mobility and interactions of proteins is key to understanding cellular signaling mechanisms.However,bulk approaches have been unable to unambiguously monitor the behaviors of the individual PM molecules without disrupting their membrane environment.Besides,transient molecular interactions cannot be identified by conventional fluorescence imaging-approaches.In the past few years,we have developed variable-angle total internal reflection fluorescence microscopy (VA-TIRFM) to image PM proteins in intact plant cells,applied single-particle techniques to protein tracking and subunit counting,provided new information on the spatiotemporal dynamics of specific molecules and their interactions.