Microscopic and Biochemical Visualization of Auxins in Plant Tissues

Auxins are a particularly notable class of phytohormones in that they regulate plant growth and development at sites of synthesis, and via a regulated polar transport system comprising PIN, ABCB, and AUX/LAX transport proteins. In order to fully understand auxin-regulated physiological processes, it is therefore essential to be able to determine where indole-3-acetic acid and related compounds are being synthesized, where they are transported to, and how much IAA is accumulating in any given tissue. Auxin may be visualized either indirectly, through the use of auxin responsive promoters; directly, through the use of radiolabelled auxin or fluorescent auxin analogs; or biochemically through extraction and mass-spectrometric quantification of auxin and auxin metabolites from target cells or tissues. Here we focus on the use of the DR5::GUS synthetic auxin promoter reporter construct, fluorescent auxin analogs, and confirmatory biochemical (high-pressure liquid chromatography tandem mass-spectrometry) visualization of auxin and auxin metabolites.