Fig. 6. dimB is required for stalk cell induction and repression of non-vacuolar cell death in response to DIF-1. (A) Repression of spore cell formation by DIF-1 was measured in an 8-Br-cAMP assay. In the absence of DIF-1, all strains produced similar numbers of spores. Only dimA^- mutant cells produced spore cells in the presence of DIF-1. Each assay was performed at least three times and the results of a representative assay are shown. dimAB^- represents the double mutant dimA^-dimB^- and AX4 is the wild type. (B) dimB^- cells were stained with DAPI without DIF-1 treatment (a,b) or after DIF-1 treatment (c,d). Micrographs were taken with phase contrast (a,c) or fluorescence microscopy (b,d). (C) dimB^- mutants produce cells with identical characteristics to those that have undergone non-vacuolar cell death. (a) Phase-contrast image showing cell morphology. Cells appear rounded and contain a dense/granular region. (b) Staining of DNA with DAPI. (c) F-actin distribution detected with phalloidin. (D) Model of DIF-1 responses based on the epistatic relationship between DimA and DimB in the 8-Br-cAMP assay.