Quantitation of transient expression of GFP in plants from 35S promoter or from a TMV vector. Top. Individual N. benthamiana leaves infiltrated with (A) A. tumefaciens (A.t.)/pCB:GFP + A.t./pJL3:P19 cell suspensions or (B) A.t.pJL43:GFP + A.t./pJL3:P19 cell suspensions. (C) Non-infiltrated control leaf. Leaves photographed (4 days post infiltration, DPI) under UV light to visualize GFP. Bottom. Micrograms of GFP produced per gram of infiltrated tissue as estimated by GFP fluorescence assay. Labelling same as in top of figure. Plant extracts prepared 4–5 DPI were analyzed with a plate-based GFP fluorescence assay. Three plants of each treatment were analyzed. Samples were analyzed in triplicate, and values averaged. Purified His-6 tagged GFP was used to generate a standard curve.