Fig. 1.

Ethylene-independent root meristem size modulation by CK. (A) Reduction of ethylene biosynthesis by AVG without interference with CK effect on the root meristem size (no difference between CK-treated and CK + AVG-treated root meristems; Student's t test, P > 0.05). (B) CK-insensitive root growth at reduced ethylene biosynthesis conditions (*statistically significant difference in root length between CK and CK + AVG-treated seedlings; Student's t test P < 0.05). (C) Reduced root meristem in the ethylene signaling mutants etr1–3 and ein2 after CK treatment (*statistically significant difference in the root meristem size between CK-treated and -nontreated seedlings; Student's t test, P < 0.05). (D) CK-resistant root growth of etr1–3 and ein2. (E) CK-induced ectopic expression of DR5::GFP reporter in outer layers of the root meristem (lateral root cap and epidermis; arrowheads). Reduction of ethylene biosynthesis by AVG diminishes the DR5 ectopic expression. CK-reduced DR5 expression in QC (asterisks). (F) Quantification of DR5::GFP expression by image analysis in QC of roots treated with CK and CK + AVG; expression of DR5::GFP is significantly reduced after CK treatment under conditions of reduced ethylene biosynthesis (*statistically significant difference between AVG and CK + AVG-treated roots, Student's t test, P < 0.05). Six-day-old seedlings grown on media containing 100 nM BA, 200 nM AVG, (if not marked differently). RM, root meristem; RL, root length; MS, Murashige and Skoog medium only; CK represented by N⁶-benzyladenine (BA); col, control Columbia seedlings. Error bars represent standard deviation (SD).