Defective pollen development in p5cs but not p5cr mutants . Pollen was collected from open flowers of 2–4 individual plants and analysed for viability by Alexander staining. The numbers in the columns indicate the total number of pollen grains analysed per genotype. A: Pollen of a p5cs1-4 single mutant plant, B: Pollen of a p5cs1-4 mutant plant additionally heterozygous for the p5cs2-1 mutation; red arrows indicate non-viable pollen grains. C: Abundance of non-viable pollen in various p5cs mutant genotypes. Capital letters indicate wildtype alleles, lower case letters indicate mutant alleles (a1 = p5cs2-1; b = p5cs1-4; Col-8 and homozygous p5cs single mutants are additionally labelled for increased clarity). D: Normal (lower left) and non-viable pollen grains from a heterozygous p5cr-1 plant at higher magnification. E: Frequencies of non-viable pollen grains in heterozygous p5cr mutants.