Figure 1.

Natural Genetic Variation in Compound-Specific Root Growth Arrest Specifically Targets the Primary Root Meristem in Col-0.

(A) Chemical structure of root growth arrest-causing DFPM.

(B) DFPM causes a primary root growth arrest phenotype in Col-0.

(C) DFPM-induced root growth inhibition of Col-0 (EC₅₀ ∼1.5 μM). Error bars mean ± sd.

(D) While Col-0 roots are sensitive to DFPM, roots of Ler, Br-0 (Brunn-0), Ts-1 (Tossa de Mar-1), Kin-0 (Kindalville-0), Bay-0 (Bayreuth-0), C24, RLD (Rschew), WS (Wassilewskija), and 42 other Arabidopsis accessions (see Supplemental Table 1 online) produced no significant growth arrest response to DFPM. The black horizontal bars mark the starting position of roots when DFPM was applied.

(E) Microscopy examination of DFPM-treated roots reveals that while root differentiation is normal, meristematic and elongation zones of the primary root are reduced in size in response to DFPM in Col-0. Note that Ler produced normal root morphology in response to DFPM exposure (left). Meristematic and elongation zones are indicated by lines and arrows. Bars = 50 μm.

(F) Deregulated DR5 promoter expression by DFPM indicates that auxin accumulation is abrogated in the root meristem after 4 d of DFPM treatment. Expression of the endodermal marker gene SCR is also altered by DFPM. Expression of the CyclinB1 promoter suggests that cell cycle activity in the DFPM-treated primary root tip is reduced. All marker lines tested here are in the Col-0 background.