C4H-GFP and CCR1-GFP are localized between secondary cell wall domains during VND7-induced protoxylem TE differentiation. A, Bright-field image of a differentiating protoxylem TE induced in VND7-VP16-GR plants, showing secondary cell wall thickenings (arrowheads). B, Maximum projection image of optical sections through the same cell shown in A, in which C4H-GFP localization is observed in the ER network that is excluded below developing secondary cell walls (arrowheads) and is adjacent to primary cell wall domains. C, Transmission electron micrograph showing laminar ER, Golgi, and mitochondria in relation to secondary cell walls of root protoxylem TEs. D and E, Maximum projection images of optical sections showing cytoplasmic localization of CCR1-GFP (D) and cytGFP (E) in control hypocotyl epidermal cells of VND7-VP16-GR seedlings without DEX induction. F to I, After VND7-VP16-GR protoxylem TE induction for 24 h, both CCR1-GFP (F) and cytGFP (G) were predominately localized in the cytoplasm between the secondary cell wall thickenings and as shown in a single median optical slice in CCR1-GFP (H) and cytGFP (I). er, Endoplasmic reticulum; G, Golgi; m, mitochondria; n, nucleus; scw, secondary cell wall. Bars = 12 μm in A, B, and D to G; 500 nm in C.