Fig. 1 in The biosynthesis, composition and assembly of the outer pollen wall: A tough case to crack

Fig. 1. Surface structure and cross-section morphology of the mature Arabidopsis pollen wall. Scanning electron micrographs (A, B) and transmission electron micrographs (C, D) of wild-type pollen at maturity. (A) Critical point dried pollen grain with reticulate exine and one visible aperture (of three). (B) Pollen wall surface structure. (C) High-pressure frozen and freeze substituted pollen grain in cross-section with dense cytoplasmic contents encased by a pollen wall. Region boxed in panel C is magnified in panel D. (D) Stratified pollen wall with electronlucent intine, electron-dense sporopollenin and heterogeneous pollen coat. The plasma membrane separates wall components from pollen cytoplasm. (E) Diagrammatic representation of the pollen wall from panel D. Arrows indicate the broad categorization of wall layers into intine (light grey) and exine. Within the exine, the structured sporopollenin (black) of the wall appears homogeneous, in contrast to the heterogeneous pollen coat (mottled grey). Bars = 2 µm (A, C) and 0.2 µm (B, D).