Mutation in AtMMS21 affects pollen number, viability, germination and growth. (A-B) Flower of wild-type and mms21-1 plants. mms21-1 produced dramatically reduced pollen grains. (C-D) Anthers of wild-type and mms21-1 plants, which are stained with Alexander’s solution. (E-F) Pollen grains of wild-type and mms21-1 plants, which are stained with Alexander’s solution. The red-stained cytoplasm indicates viable pollen grains, whereas nonviable pollen grains are stained blue. (G) Percentage of pollen germination. (G-I) In vitro pollen tube growth assay. White arrows indicate long pollen tubes exhibiting branched tips, and red arrows indicate short pollen tubes tip with obviously swollen. Bars = 5 mm in (A-B), 2 mm in (E-F, H-I).