Fig. 7. Cytological and molecular characterization of phenotypic defects in the shoot apical meristems of antisense plants. (A-D) DAPI-stained sections of wild-type (A,B) and antisense (C,D) SAMs. Note the tunica/corpus organization in a wild-type SAM (A) is disrupted in the antisense SAM (C). The apical dome is enlarged and the cells of the antisense SAM are larger. (B,D) Higher magnification of A and C. The chromatin appears partially condensed and stretched. (E,F) Toluidine Blue-stained sections of 8-day-old wild-type (E) and 18-day-old antisense (F) plants. The enlarged SAM in F illustrates large disorganized cells. (G) Scanning electron micrograph of an 18-day-old antisense plant showing the enlarged and irregularly shaped SAM (M). (H,I) SEM of a wild-type (H) and an antisense (I) meristem, illustrating well patterned and regularly shaped cells on an emerging leaf of wild type (H), but a disorganized pattern of irregularly shaped cells in the antisense line (I). Note that the SAM in l H is hidden by the leaf primordia, but has clearly emerged in the antisense plant (I). (J-L) Histone H4 expression in the SAM of a wild-type (J) and an antisense (K) plant as seen by RNA in situ hybridization. (J) High level expression of histone H4 is observed in the wild-type SAM, leaf primordia and developing young leaves. (K) Apex of an antisense plant showing a dramatic reduction in histone H4 expression in the enlarged SAM. (L) Higher magnification photograph of an antisense SAM, illustrating that few cells are histone H4 positive. Bar=50 µm. Scale bars: 50 µm (A,C); 10 µm (B,D); 150 µm (G); 60 µm (H,I); 50 µm (J); 100 µm (K); 50 µm (L).