Fluorometric quantification of GUS activity in transgenic tomato plants. (A) Tissues from transgenic plants harboring PCaMV35S::GUS (constitutive promoter), (B) ShCYC-B full-length promoter D0-908::GUS and its deletion fragments D2-578::GUS and D3-436::GUS, respectively. Samples from 2-3 lines from single copy transgenic events (two events per construct) were pooled and used for quantitative MUG assay. Plant tissues were homogenized in protein extraction buffer. The supernatant was used for protein quantification and fluorometric assay. Reading at zero time point served as a control. The amount of 4-MU was determined from a standard curve. GUS activity was expressed as pmol 4-MU mg protein-1 min-1. Data are presented as the mean (± standard error) of GUS activity from three independent determinations.