Figure 2. Electron micrographs of in situ hybridization with biotin labeled 18S rDNA probe on sections through root tip meristematic tissue of Q. robur.

Hybridization area was detected with DAB. Labeled condensed chromatin lies outside or close to the nucleolus (A and B, black arrows), protruding into the nucleolus (B, black arrow) and inside the nucleolus near the nucleolar border (C, black arrows). Diffuse hybridization signal that corresponds to completely decondensed DNA is seen inside the nucleolus (A, B, C, white arrows). Unlabeled chromatin corresponding to the NOR-bearing chromosome can be seen near the nucleolus (B, black arrowhead) and protruding into it (A, black arrowhead). Letter «n» marks the nucleolus. Scale bar is 2.5 µm.