Nuclear DNA degradation and unspecific in situ hybridization signal in immature Scots pine seed. Nuclear DNA degradation and an unspecific in situ hybridization signal in the nucellar layers of a developing Scots pine seed. (A) Fragmented DNA (arrows) in the AO-stained section. (B) TUNEL-positive nuclei (arrows) and autofluorescence of granulous phenols (arrow heads) in the nucellar layers. Localization of diamine oxidase (DAO) mRNA transcripts by in situ mRNA hybridization (arrows) with antisense (C) and sense (D) probes resulted in equal hybridization signals in the cells of the nucellar layers. M = megagametophyte, N = nucellar layers.