DIR1 expression in leaves using the DIR1 promoter:GUS plant lines. (A) DIR1pro:DIR1-GUS-29/dir1-1 and DIR1pro:GUS-11/Ws plants lines (3.5 wpg) were left untreated (U), mock-inoculated (M) or inoculated with 106 cfu ml-1 of SAR-inducing PstavrRpt2 (I) and harvested at 14 hpi, 20, 40 hpi and subjected to histochemical GUS analysis. Staining pattern were similar at all time points, therefore 14 hpi is shown for DIRpro:DIR1-GUS-29/dir1-1 and 20 hpi leaves for DIRpro:GUS-11/Ws. Systemic leaves were also collected from plants that were SAR induced (S). Representative leaves from each line were photographed in a single sitting without adjusting microscope settings and two different leaves are shown. The bar represents 100 μm. Measurement of relative GUS activity in (B) DIR1pro:DIR1-GUS-29/dir1-1 and (C) DIR1pro:GUS/Ws. Leaves from the experiment presented in panel A were scored using a subjective relative scale of 0 to 4, with 0 representing little GUS staining and 4 representing intense GUS staining. U = uninoculated, M = mock-inoculated, I = inoculated leaf from SAR-induced plants, S = systemic leaf from SAR-induced plants. The asterisk (*) denotes a significant difference (student's t test) between mock-inoculated leaves and leaves induced for SAR. This experiment was repeated once with similar results.