Fig. 5. Seedlings expressing the auxin response reporter DR5::GUS. DR5 is expressed more strongly in wild type (A,C,E) than in seu-3 (B,D,F). (A) Roots assayed for GUS activity show GUS staining extending from the root meristem into the root cap (arrowhead) and stele (arrow) in wild type. (B) seu-3 roots display a substantial decrease in GUS product, with only weak DR5 expression in the root cap (arrowhead), and none in the vasculature (arrow). (C,D) Five-day-old seedlings show first leaves with more extensive GUS activity in wild type, spatially marking incipient and developing veins, whereas in seu-3 GUS product is seen only at the distal leaf tip and in hydathodes. (E,F) Seven-day-old seu-3 seedlings do not show a recovery in GUS activity. As leaves grow and mature, wild-type GUS activity parallels the basipetal differentiation of vascular tissue. No GUS product is seen in seu-3 leaves at similar stages (compare 1, 2 and 3). Genotypes described are in Col.