In situ determination of early fiber-specific expression of three important genes. In situ hybridization: (A–C) a putative MAPK (P3D03); (E–G) a putative ABP (P1F01); (I–K) a profilin (P1E05). (A), (E) and (I) show antisense hybridization to cross-sections of 2 d.p.a. wild-type upland cotton. (B), (F) and (J) show antisense hybridization to 2 d.p.a. fl mutant ovules. (C), (G) and (K) show negative controls of 2 d.p.a. wild-type cotton with the sense strand of each cDNA. (D, H and L) Positive controls of 2 d.p.a. wild-type cotton with the antisense strand of a cotton ubiquitin. Blue signals represent mRNA of the tested genes. f, fiber cells; oi, outer integument; ii, inner integument.