Figure 7.

Development of marginal trichomes. A and B, Comparison of wild-type plants with tt8, gl3, and tt8gl3 mutants for the developing leaf stage by light microscopy (A) and scanning electron microscopy (B). C, Quantification of marginal trichomes on developing and mature leaves (from 1-week-old and 4-week-old seedlings, respectively) of single and double bHLH mutants. In both stages, three zones were arbitrarily defined based on the distance from the visible leaf margin. From the leaf margin to the center, these zones are M1 (margin 1), the outer 5% (calculated on the total leaf surface) that includes the visible margin; M2 (margin 2), the 5% inward layer adjacent to M1; and L (lamina), the central region. Trichome numbers in leaves of the Col-0 wild type for each zone were set at 100% and corresponded to 12 (M1), 15 (M2), and 33 (L) in developing leaves and to 49 (M1), 32 (M2), and 73 (L) in adult leaves. Error bars represent se (n = 15). D, Trichome development in the tt8 mutant after transfer from mock (K1) to phytohormone-containing medium.