Fig. 7. Expression of Pro_ACL5:DT-A alters plant growth and xylem development. (A) The general phenotype of 1-month-old wild-type, Pro_ACL5:DT-A heterozygous line 4, Pro_ACL5:DT-A homozygous line 4 and acl5 seedlings. (B-D) Resin-embedded transverse sections of 2-month-old acl5 (B), Pro_ACL5:DT-A homozygous line 4 (C) and wild-type (D) hypocotyls stained with Toluidine Blue. (E-G) Appearance of xylem elements after maceration of the hypocotyls of 2-month-old acl5 (E), Pro_ACL5:DT-A homozygous line 4 (F) and wild type (G). Asterisks indicate the presence of xylem fibers in the wild-type (G). (H-Q) Expression of Pro_ACL5:GUS in wild-type (H-J), Pro_ACL5:DT-A homozygous line 4 (K-N) and acl5 seedlings (O-Q). Histochemical GUS staining is shown for hypocotyls of whole mounts (H,J,K,M,N,O,Q) and transverse sections of resin-embedded hypocotyls (I,L,P). Xylem differentiation was delayed in Pro_ACL5:DT-A seedlings, and comparisons were therefore made between 3-day-old wild-type and acl5 and 6-day-old Pro_ACL5:DT-A in vitro grown seedlings. The arrows indicate expression of Pro_ACL5:GUS and therefore DT-A toxin production in the incipient vessel elements (with first signs of secondary cell wall deposition in cell corners) of the Pro_ACL5:DT-A seedlings (L). sx, secondary xylem; vc, vascular cambium. Scale bars: 20 µm in I,J,L,M,N,P,Q; 50 µm in E,F,G,H,K,O; 100 µm in B,C; 200 µm in D.