Fig. 7. Differences in the shape of wild-type and phmyb1 mutant cells in petals of the unstable phymb1 mutant. (A) SEM micrograph of the inner epidermis in which a revertant sector can be seen on a background of mutant cells that retain a flatter conical shape. (B,C) Freeze-fracture across one sector of the inner epidermis showing in detail the shape of revertant wild-type cells (C), which grow to a greater length than mutant cells (B). (D) The outer epidermis of unstable phmyb1 lines, showing sectors of revertant conical cells and flat mutant cells, both with lobed base shapes. Trichomes (t) also develop in the outer epidermis of Petunia hybrida petals but are unaffected by the inactivation of the PhMYB1 gene. Scale bars: 100 µm in A,D; 20 µm in B,C.