Protein extraction and fluorometric GUS assays

Assays for GUS activity in infected leaf discs were based on the protocol as described by Jefferson et al. (1987) using 4-methyl-umbelliferyl glucuronide (4-MUG) as the substrate for the fluorescent assay (Jefferson et al. 1987). Proteins were quantified using the Bradford assay using Bovine Serum Albumim (BSA) as the standard (Bradford 1976). Fluorescence was measured by a spectrofluorometer (Hitachi F-4500). The excitation wavelength was 365 nm and the emission wave length was 455 nm.