Microscopy and phenotypic characterization
Pollen viability was assessed using Alexander’s staining. For scanning electron microscopic (SEM) analysis, mature pollen grains from freshly dehisced anthers were mounted and coated with gold on stubs. The samples were then immediately observed using FESEM (SU8010). TEM (transmission electron microscopy) analysis was performed as described previously (Z. B. Zhang et al., 2007). The procedure of semi-thin section and lipid staining were performed as described previously (Lou et al., 2014; Z. B. Zhang et al., 2007).