Fig. 3. The vacuole collapses early during vessel maturation in acl5. (A-D) Xylem anatomy and cell morphology of the wild-type. (E-H) Xylem anatomy and cell morphology of acl5. An overview of the xylem tissues (A,E) reveals the absence of fiber differentiation in acl5. Individual vessel elements are shown during early maturation (B,F), moderate maturation (C,G) and late maturation (D,H). All panels represent electron microscopy images of transverse sections from the hypocotyls of 3-week-old plants. The central vacuole is absent in maturing (i.e. secondary cell wall depositing) vessel elements of acl5, even at the earliest stage of maturation (F). f, fiber; cv, central vacuole; n, nucleus; v, a vessel element that is either living or undergoing cell death. The arrows indicate presence of secondary cell walls. The asterisks indicate dead, autolyzed vessel elements. Scale bars: 10 µm in A,E; 2 µm in B-D,F-H.