Fig. 3

Differential interference contrast (DIC) images of Beta vulgaris ovules cleared by the modified procedure. The material was pre-treated with 1 M hydrochloric acid combined with Schiff’s reagent, and subjected to shaking and vacuuming during infiltration steps. a Ovule at post-fertilization stage. The proembryo in the embryo sac slightly visible due to the presence of the developing seed coat (negative control). b–f Ovules after optimization of the modified procedure. b Ovule with an embryo sac. c Micropylar pole of the ovule with a young embryo sac. d Ovule with a mature embryo sac after polar nuclei fusion. e, f Before the maceration step with hydrochloric acid, the material was pre-treated with 95% sulfuric acid in order to manually remove the seed coat. e Torpedo-shaped embryo. f Apical part of a mature embryo with embryonic tissues of hypocotyl and radicle surrounded by a root cap. b–d Pre-fertilization stages; a, e, f post-fertilization stages. Black dotted line surrounds an embryo sac. co, cotyledon; ec, egg cell; en, cellular endosperm; es, embryo sac; hc, hypocotyl; ii, inner integument; n, nucellus; nc, nucellar cap; oi, outer integument; p, perisperm; pc, parietal cells; pe, proembryo; r, radicle; rc, root cap; s, synergid; sc, seed coat; sn, secondary nucleus of the central cell. Scale bars: 20 µm (c, d), 50 µm (b), 100 µm (a, e, f)