Nucleic acid fragmentation in immature Scots pine seed. Nucleic acid fragmentation in the embryo surrounding region (ESR), cells of the megagametophyte tissue and the degenerated suspensor tissue in a developing Scots pine seed. (A) In the acridine orange (AO) -stained section, cell wall remnants and degraded nucleic acid formed a zone between the ESR and the developing embryo (arrows). (B) TUNEL-positive nuclei of the megagametophyte cells in the ESR (arrows). (C) TUNEL-positive signal in fragmented DNA among the cell wall remnants in the corrosion cavity (arrow). (D) AO-stained section with subordinate embryos and fragmented nucleic acids in the corrosion cavity close to the remnants of the degenerated suspensor tissue (arrows). CC = corrosion cavity, E = embryo, M = megagametophyte.