Turgor and curvature of the apical cells.

(A) Turgor value in apical cells measured using the limit plasmolysis method [34]. Different osmolarities (Ce) were applied to Ectocarpus filaments, and plasmolysis was monitored in apical cells (n > 100 for each osmolarity). Limit plasmolysis concentration (Cpl), which is the solute concentration for which 50% of apical cells are plasmolyzed, was 1,980 mOsm L−1 (each color represents an independent experiment [n = 3]). Corrections, as explained in the Materials and methods section, led to a final turgor value of 0.495 MPa. Data are available as Supporting Information S3 Data. (B) Apical cell curvature. (Left) Ectocarpus apical cell contour was drawn manually on microscope images. (Middle) From the contour of each cell, a smoothed cubic spline was computed. (Right) The meridional curvature of each cell was calculated from the discretized contour. All curvature series (for n = 17 Ectocarpus apical cells, S2 Fig) were averaged (blue curve, SD shown as light blue curves), and the mean curvature was used to create a mean contour. Circumferential curvature (green curve) was then inferred from the mean contour. Gray lines are for curvature = 0. The same procedure was used for 6 tobacco pollen-tube cells.