Figure 4.

Micrographs showing (A) the inhibition of self-pollen and the inability of the emerging pollen tubes to invade the papilla cell wall (incompatibility), and (B) the penetration of cross-pollen tubes into the papilla cells (compatibility) in Brassica rapa L. Yellow arrow indicates the penetrated pollen tubes. With aniline blue staining, pollen tubes appear as distinct tubes with prominent dots, because callose plugs in the pollen tubes fluoresce brightly. In contrast, vascular bundles and other tissues do not fluoresce brightly, as shown in (A). Bar = 200 µm. (Courtesy of Masaaki Osaka and Ken-ichiro Hiroi, unpublished data).