Fig. 4. Further exploration of the function of AmMYBML1. (A) Freeze fracture SEM through the corolla hinge of A. majus. This flower was taken from a mixta mutant, which has flat epidermal cells on the inner epidermis of the corolla lobes. However, a few conical cells are present in the hinge region (indicated by arrows), presumably as a result of AmMYBML1 activity, which is expressed, in lobes, just in the hinge region. (B) Conical cells (indicated by arrows) in the hinge region of an EMS-induced mixta mutant line are shown in more detail. (C) In situ hybridisation showing the expression of AmMYBML1 in the mesophyll tissue of the folds of the ventral petal (arrowed) on the adaxial side of the hinge. ct indicates the corolla tube tissues; cl the corolla lobe tissues. (D) The mesophyll of the folds of the petal hinge consists of compact and tightly packed cells, especially towards the adaxial side. (E) The mesophyll cells of the petal lobes are more loosely packed (compare with D). (F) The cells of the petal mesophyll have projections which contact other cells. (G) Transverse section through wild-type tobacco petal lobe for comparison with H. (H) Section through petal lobe of a tobacco line ectopically expressing AmMYBML1. Expression of AmMYBML1 thickens the petal through increased expansion of the mesophyll cells (compare with G). Scale bars: 200 µm.