TDIF-Sensitive Xylem Formation in wox4 Mutants TDIF-Sensitive Xylem Formation in wox4 Mutants.(A) Effects of 1 μM TDIF on 10-d-old leaf veins of different strains. TDIF-Sensitive Xylem Formation in wox4 Mutants.(A) Effects of 1 μM TDIF on 10-d-old leaf veins of different strains. TDIF caused fragmentation of xylem strands (indicated by white arrowheads) in wox4-1 and in the wild type but did not in tdr-1 or the tdr-1 wox4-1double mutant. Veins are outlined in red, and xylem strands are outlined in blue.(B) Quantification of the effects of TDIF. The blue and white boxes indicate the frequencies of the xylem-absent and xylem-present veins, respectively.Bars = 100 μm in (A). Error bars indicate se, n = 8; *Student’s t test significance at P < 0.01 for different means of the frequency of xylem-absent veins in (B). Yuki Hirakawa et al. Plant Cell 2010;22:2618-2629 ©2010 by American Society of Plant Biologists