Semi-thin sections of developing Arabidopsis anthers from a transgenic At80MD plant (line 13). A. Stage 8; vacuolated tapetum cells and enlarged microspores. B. Stage 10; tapetum cells are highly vacuolated and enlarged. Microspores commence degrading. C. Stage 11; microspores remain vacuolated, enlarged tapetum with reduced cytoplasm. D. Stage 12; degenerated tapetum and collapsed pollen grains. MSp, microspores; PG, pollen grains; Sm, septum; T, tapetum. Scale bars = 25 μm in A, scale bars = 50 μm in B, C and D.