Quantitative GUS Activity Assay of Plant Extracts

INTRODUCTION The activity of ß-glucuronidase (GUS) can be accurately determined in extracts of plant tissue using 4-methylumbelliferyl ß-D-glucuronide (4-MUG) as a substrate. Upon hydrolysis by GUS, the fluorochrome 4-methyl umbelliferone (4-MU) is produced. Using excitation at 365 nm and measuring emission at 455 nm, the amount of 4-MU produced can be quantified. Under these conditions, background fluorescence from the substrate is negligible, especially if the appropriate filter is selected.