Phenotype of ldc mutants and molecular identification of the spch-5 mutation. A, DIC images of entire 15-d-old abaxial cotyledons of Col-0 and ldc. B, Growth phenotypes of 40-d-old Col-0 and ldc plants. C, Diagram of SPCH showing the spch-5 mutation (red) causing an Arg-to-Trp change within the bHLH domain (blue box). Other alleles have point mutations outside the bHLH domain (spch-1 and spch-2) or T-DNA insertions (spch-3; black triangle). D, DIC micrographs showing the abaxial epidermis of 23-d-old cotyledons and 10-d-old hypocotyls in Col-0, spch-5, and the complemented spch-5/SPCHpro:SPCH-GFP line. Stomata are false colored in purple for easier identification. Stomatal clusters are marked by brackets. E, Graphs representing stomatal index, stomatal density, and organ area in the abaxial epidermis of 23-d-old cotyledons. Gray and orange bars denote Col-0 and spch-5, respectively. Asterisks indicate P < 0.05 (Student’s t test; n = 10), and n.d indicates P > 0.05. Error bars represent se. Bars = 0.5 mm in A and 50 µm in D.