Growth of transgenic tobacco plants expressing the sense (XS) or antisense (XAS) copy of pkv. (A) Three week-old in vitro plantlets of control (X), XS and XAS showing the reduced (XS) or enhanced (XAS) root production (arrows). (B) Five-week old plants in soil showing the dwarfing phenotype of XS. (C) Fully mature greenhouse-grown plants showing the increased height and flowering of XAS and the dwarfing habit and reduced/delayed flowering of XS. (D) Transverse petiole sections from leaves of mature control (X), XS, and XAS tobacco plants. Sections were observed by light microscopy without staining. Petioles of the fifth leaf from the base were taken from each plant. Original magnification, 100 ×. Arrows designate the columns of lignified xylem elements.