Immunolocalization of CBP70 on cross-sections of the node of etiolated maize seedlings. LR White-embedded sections of the node from dark-grown 4-d-old maize seedlings were analysed. Sections were incubated with mouse anti-CBP70 mAb of the second group (14A4), biotinylated anti-mouse antibody, and streptavidin-alkaline phosphatase conjugate. (F) A negative control was the same as in Fig. 2: sections were treated with non-immune serum. (A, C, D) Post-staining with safranin. (A) Immunochemically stained cross-section of the node. Broken lines designate the boundaries of leaves encircling the stem axis; figures indicate leaf numbers in the order of their formation; ap, stem apex. CBP70 was detected in plastids of the second leaf (black arrows). (C) A 2-fold magnification of the fragment of the second leaf. (D) Enlarged fragment of (C). (C, D) Plastid heterogeneity in CBP70 content is seen: plastids containing CBP70 (black arrow); plastids not containing CBP70 (white arrow). (B) Cross-section of the second leaf without post-staining with safranin. The arrangement of CBP70-containing plastids around the nucleus is seen (black arrow). (E) Stem apex without post-staining with safranin. A great amount of plastids containing CBP70 is seen (black arrows). (B, E) Plastids with CBP70 are absent from the zones of active cell division. CBP70 was recognized in these zones in the nuclei and cytoplasm (black triangles). Scale bars are 50 μm (A), 25 μm (B, C, E).