Fig. 8. Effect of the phmyb1 mutation on the shape of Petunia flowers. (A) Wild-type flowers seen from the top (a) and side (d). Top view (b) and side view (e) of an unstable phmyb1 flower. A revertant sector occupies two-thirds of the corolla lobe (left). The mutation causes the corolla (right third) to recurve downwards, whereas the wild-type sector stays in a straight position. (c) The effect of the mutation can also be clearly observed in flowers where most of the corolla is recurved downwards, except for the area (top left) corresponding to a PhMYB1⁺ revertant sector. (B) PhMYB1 affects the lateral expansion of cells. Cells were counted in a given area of mutant and wild-type sectors in petals of phmyb1 unstable lines, in the inner and outer epidermal cell layers. (Left) Example areas of the inner epidermis chosen for cell counts in a revertant sector (black box), and in an equivalently sized region of an adjacent mutant area (white box). The bar chart shows that in the inner epidermis, the number of cells per unit area was lower in phmyb1 mutant areas as compared with wild-type revertant sectors, whereas in the outer epidermis there was no significant difference. The values shown are the means from ten values±s.e.