Fig. 4: Root BR determines the biomass distribution along the root irrespective of shoot BR.

a An illustration depicting equal biomass for a distinct total root length raises the question of how carbon is distributed. b Confocal images showing optical longitudinal and cross-sections taken 50 μm from the quiescent center (QC) of the primary root meristem, in WT/WT, WT/cpd, cpd/cpd and cpd/WT (5-week-old). Scale bar, 50 μm. Note the disorganized cell files in cpd root combinations. c Whole meristem diameter and d stele diameter in roots as in (b) n: WT/WT = 12, WT/cpd = 19, cpd/cpd = 6, cpd/WT = 14. e–i Quantification of cell wall thickness in longitudinal wall of the outer epidermis (e), radial wall of the outer epidermis (f) and wall between neighboring pericycle cells (g), observed in cross-sections in WT (n = 3, green) and cpd (n = 3, magenta) roots. The corresponding cell walls are depicted in pink in the accompanying illustration (h). In outer epidermal radial walls, 15–20 cells were measured, with 20–30 measurements taken along the cell wall of each cell. In outer epidermal longitudinal walls, 2 cells were measured, with 10 measurements taken along the cell wall of each cell. In the pericycle radial walls, 12–15 cells were measured, with 13–18 measurements taken along the cell wall of each cell. Each boxplot represents one plant and each dot represents measurement in a different cell wall. In boxplots, the center corresponds to the median, the lower and upper hinges represent the first and third quartiles, and the whiskers extend to the largest and smallest values within 1.5× the IQR from the hinges. Generalized Linear Mixed Model (glmm analysis, see “methods”) shows that cpd thickness is significantly higher in both epidermis and pericycle. i, j Transmission Electron Microscopy representative images of longitudinal and cross-section of the primary root elongation zone in WT and cpd showing the outer epidermal cell wall (longitudinal section, scale bar, 1 μm; cross section, scale bar, 0.5 μm) and the cell wall between neighboring pericycle cells (scale bar, 1 μm).