Fig. 1

Deposition pattern of apoplastic barriers in ovule and seed integuments. a, b, d, and e Fluorescence images of longitudinal sections of wild type ovules at stages (a) 2-i, (b) 2-iv, (d) 3-iv and (e) 3-VI [54], stained with auramine O (yellow). c Fluorescence image of a three-dimensional reconstruction of a wild type ovule at stage 2-IV stained with auramine O (yellow). f to j Fluorescence images of longitudinal sections of wild type seeds at different developmental stages stained with auramine O (yellow). Seed cell walls are counterstained with calcofluor (cyan). k to q Transmission electron micrographs showing the IAB of wild type ovules and seeds. k Mature ovule (stage 3-VI). l Close-up image of (k). m and n Globular embryo stage seed. o and p Torpedo embryo stage seed. q Mature ovule (stage 3-VI). Black arrows indicate the IAB. Yellow arrows indicate the presence of the IAB between endothelium and nucellus/female gametophyte, whereas red arrows its absence. en, endothelium; nu, nucellus; es, endosperm; fg, female gametophyte. Ecotype Col. Scale bars: (a) 10 μm, (b) and (c) 20 μm, (d) and (e) 30 μm, (f) to (j) 50 μm, (k) and (m) 1 μm, (o) 2 μm, (l), (n) and (p) 0.25 μm, (q) 10 μm.