Mechanics of radial proliferation in plant roots

How do multicellular organs coordinate radial proliferation across distinct layers? Combining Arabidopsis cross-sections with a minimal mechanical model and an ablation assay that triggers robust radial proliferation we show that cell-type specific circumferential stresses correlate with cell-type radial proliferation.

The elastic model reproduces two robust features: (i) circumferential stresses are substantially lower in ablated roots where radial proliferation is enhanced than in controls; and (ii) the stele undergoes a sign change in circumferential stress, switching from net compression to tension. Intuitively, hoop remodeling offloads circumferential load to the stele thereby promoting continued radial growth.

The framework yields sharp, testable predictions: (1) a drop in the outer cell file’s (epidermal/ground-tissue) microtubule order at remodeling sites (stress realignment), (2) cell-type-specific radial divisions (pSCR::CYCD6 vs pWOL::CYCD6) should shift the system along a geometry–mechanics axis with distinct consequences for vascular file number; (3) outer-wall softening should redistribute strain without necessarily increasing inner files—discriminating constraint from instruction.

Significance. Our combined experimental and modelling approach yields a predictive map of stress regimes, explaining radial proliferation during normal growth and after injury thereby offering a quantitative route to couple cell-cycle programs to whole-organ mechanics.