Catalase ( CAT ) localization by in situ mRNA hybridization in immature Scots pine seed. Localization of catalase (CAT) mRNA transcripts by in situ mRNA hybridization in a developing Scots pine seed. (A and B) In addition to the specific in situ hybridization signal (blue colour) in the embryo, unspecific signals (arrows) were found in the broken megagametophyte cells in the embryo surrounding region (ESR) (A) and in the degenerated suspensor tissue in the corrosion cavity (B) in the section hybridized with the CAT antisense probe. (C and D) With the CAT sense probe, no signal was found in the embryo but unspecific signals (arrows) were detected in the ESR cells of the megagametophyte and in the arrow-shaped region in front of the expanding corrosion cavity (C) as well as in the degenerated suspensor tissue in the corrosion cavity (D). CC = corrosion cavity, E = embryo, M = megagametophyte.