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Geometric and mechanical guidance: Role of stigmatic epidermis in early pollen tube pathfinding in arabidopsis

Fig 6

Role of cell wall mechanical anisotropy in pollen tube guidance.

(A) Schematic representation of the papilla cell wall anisotropy and alignment strength factor . Y_lg (Y_ci) stands for the effective stiffness in the longitudinal (circumferential) direction within the papilla wall. Note that we considered Y_ci (Y_lg) to be the same in the inner and outer papilla wall leaflets. When , is negative, the longitudinal direction is softer (narrow blue arrow) compared to the circumferential one (large blue arrow). When , is positive, the circumferential direction is softer compared to the longitudinal one. A positive value of the alignment strength factor favours a circumferential pollen tube growth whereas a negative value of favours a longitudinal growth. We explored how the anisotropy can influence the alignment strength factor and hence the pollen tube growth direction (question mark). (B,C) Indentation ratio (upper panels) and alignment strength factor (lower panels) for circumferential (circ, solid line) and longitudinal (long, dashed line) tube growth depending on the papilla wall mechanical anisotropy and the effective rigidity of the papilla wall (, B: , C). The calculations were done using the ratio for ktn1-5 geometry (m/m, depicted in blue, B) or for WT geometry (m/m, depicted in orange, C). The grey lines correspond to the experimentally measured indentation ratios on ktn1-5 and on WT papillae. Additional calculations for ktn1 geometry with rigid cell wall, WT geometry with soft cell wall and intermediate wall rigidity () are provided in S1 Text. The dashed red line highlights the isotropic case ().

doi: https://doi.org/10.1371/journal.pcbi.1013077.g006