The phenotype of S1 mutant. The spikelet of WT (a) and S1 mutant (g). The pollen fertility of WT (b) and the S1 mutant (h) by iodine staining magnified 20×. Transverse section analysis of the anther development in WT (c–f) and the S1 mutant (i–l). Locules from the anther section of WT and at stage 6 (the microspore mother cells stage), stage 9 (the young microspore stage), Stage 10 (the vacuolated pollen stage), and stage 13 (the mature pollen stage). E, epidermis; En, endothecium; T, tapetum; MMC, microspore mother cells; Msp, microspores; MP, mature pollen; DMsp, degenerated microspores; DP, degenerated pollen. Scale bar: 50 μm.