Expression of E. coli PPase in roots of transgenic potato plants (‘Desiree’). (A) Schematic structure of the construct used for transformation of potato plants. STLS, leaf-stem-specific promoter; 35S, 35S CaMV promoter; Ω, TMV-U1 translational enhancer; T, octopine synthase terminator. (B) Northern blot analysis of roots of E. coli PPase-expressing plants (UPPa II-2) as well as of wild-type plants (Desiree WT) under aerated conditions, C, and after 4 d of hypoxic treatment, H, with two replicates each. (C) Enzymatic activity of soluble PPase in potato root extracts after 4 d of hypoxia, H, compared with aerated conditions, C. Activity values are means of at least 8–12 samples ± s.e. from four independent experiments. Asterisks show significant changes between aeration and hypoxia (*) and between wild-type and transgenic plants (**) at the 5 % level (t-test).