The impact of the MDCA-induced lignin reduction on the plant phenotype. A, Effect of MDCA treatment on the Casparian strip formation (white; no complementation) in Arabidopsis seedlings 5 DAG and complementation by exogenous application of two monolignols (gray; complementation): 50 μM of each coniferyl alcohol and sinapyl alcohol, which allows for the formation of a functional Casparian strip (n = 10). See text for additional explanation on this experiment. B, Root phenotype of seedlings (12 DAG) grown on 0.5 × MS-medium supplemented with MDCA and monolignols (n > 20; scale bar: 1 cm). (C and D) Combined effect of monolignols and MDCA on the primary root length of Arabidopsis seedlings 12 DAG (n > 20) and lateral root density of seedlings 12 DAG (n > 15). Seedlings were grown on 0.5 × MS medium supplemented with 0, 2.5, or 10 μM MDCA. Monolignols (coniferyl alcohol and sinapyl alcohol; 50 μM each) were added to the tissue culture medium, where mentioned (complementation). Error bars represent sds and asterisks were used to indicate statistically significant differences compared to the corresponding mock-treated control sample, as determined by Dunnett’s test P values: *P < 0.05, **P < 0.001, ***P < 0.0001.