Figure 1

Ovule phenotypes of wild type, ino and ant. A comparison of wild type (A – C) ovule development with ino (D – F) and ant (G – I) using scanning electron and fluorescence microscopy. Ovules are shown at developmental stage 2-IV (A, D, G), and 4-IV (B, E, H). (A, B) In wild type ovules, the two integuments grow as sheaths around the nucellus until it is fully enclosed and the outer integument envelopes the inner integument. (D, E) In contrast, ino mutant ovules show only inner integument growth and this structure encloses the nucellus but does not cause curvature of the ovule at maturity. (G, H) ant ovules do not initiate integuments but do elongate and form a swollen region at the chalaza. The ant nucellus is naked at maturity. (C, F, I) Ovules at anthesis were cleared and stained for callose accumulation to identify non-functional embryo sacs that can be seen as brightly fluorescing structures in ino mutants (arrow, F) and that are absent in wild type (C). Mature ant ovules (I) lack embryo sacs, but show callose fluorescence associated with chalaza and nucellus. c, chalaza; f, funiculus; ii, inner integument; oi, outer integument; n, nucellus. Scale bar = 15 μm in A, D, and G; 20 μm in H; 25 μm in B and E; and 45 μm in C, F, and I.