Microscope images of plant specimens showing expression of GUS markers, besides being very beautiful, provide useful information regarding various biological processes. However, the information extracted from these images is often purely qualitative, and in many publications is not subjected to quantification. Here, we describe a very simple quantification method for GUS histochemical staining that enables detection of subtle differences in gene expression at cellular, tissue, or organ level. The quantification method described is based on the freely available image analysis software ImageJ that is widely used by the scientific community. We exemplify the method by quantifying small and precise changes (at the cellular level) as well as broad changes (at the organ level) in the expression of two previously published reporter lines, such as the pPILS2::GUS and pPILS5::GUS. The method presented here represents an easy tool for converting visual information from GUS histochemical staining images into quantifiable data and is of general importance for plant biologists performing GUS activity-based evaluation of reporter genes.
Keywords: Auxin; GUS staining; ImageJ; PILS; Quantification; Reporter gene expression.