a, Zonation of 4-day-old wild-type root. Arrows and arrowheads indicate youngest protoxylem cell. b, c, Frequent cell division, monitored by the G2/M-phase cell cycle marker CYCB1;1–GFP, occurs close to the quiescent centre (arrow) in wild-type meristem (b). This domain shifts shootward with increased PLT2 dosage (that is, homozygote pPLT2:PLT2-YFP in Col background; green and green/yellow channels shown) (c). d, Twenty-four hours induction of PLT2–YFP in the vascular tissue (left) locally inhibits xylem differentiation (arrow, first xylem element), while PLT2–YFP induction in epidermis (right) inhibits root hair formation (arrowhead, first root hair). Propidium iodide highlights cell wall and protoxylem in b–d. Scale bars, 50 μm.