PMC

Model of the action of type III (At5g62080) and non-type III s in exine formation. Exine begins to appear at stage 8, and the formation is complete at stage 11. In tapetum cells, secretory vesicles derived from the - system contain s bound or unbound to -produced exine precursors. s and exine precursors are released into the locule, where unbound s may or may not bind to free exine precursors. s and exine precursors, unbound or bound, move to the microspore (MSP) surface, where exine is assembled. Type III s, but not other s, remain in exine as permanent constituents. Other exine precursors produced by cytosolic enzymes in tapetum cells are transported to the locule via plasma membrane ABCG26 and, with or without binding to s in the locule, move to the exine for assembly.

Scanning electron microscopy photographs of Limonium ovalifolium (a–f) and L. multiflorum (g–l) pollen grains. a Dehisced anther with a few pollen grains still inside; b Spheroid tricolpate pollen grain with microreticulate exine surface (polar view); c Ellipsoid grains with macroreticulate exine surface (diverse equatorial views); d Pollen grain with coarsely reticulate exine surface with a large reticulum (polar view); d Detail of the irregular macroreticulate exine net with spinose side walls; f Detail of the reticulum with strait spaces in microreticulate exine surface; g Dehisced anther without pollen grains; h Radiosymetric pollen grain with psilate exine ornamentation; i Bilateral pollen grains with distinct dimensions; j Bilateral pollen grains showing perforate exine surface with no prominent spines; k Pollen grains with verrucate or warty exine surface with colpi position denounced; l Pollen grain with perforate exine surface and with colpi position denounced

Pollen of Triticum monococcum subsp. monococcum (sample INA-44): A1, complete non-acetolysed pollen grain at scanning electron microscopy (SEM) at 5000× magnification (2009 batch); A2, detail of the non-acetolysed exine at SEM at 20 000× magnification (2009 batch); A3, detail of the acetolysed exine at phase-contrast microscopy (2011 batch); A4, complete acetolysed pollen grain at SEM at 5000× magnification (2012 batch); A5, detail of the acetolysed exine at SEM at 20 000× magnification (2012 batch); A6, detail of the acetolysed exine at SEM at 30 000× magnification (2012 batch). Pollen of Triticum monococcum subsp. sinskajae (sample INA-43): B1, complete non-acetolysed pollen grain at SEM at 5000× magnification (2009 batch); B2, detail of the non-acetolysed exine at SEM at 20 000× magnification (2009 batch); B3, detail of the acetolysed exine at phase-contrast microscopy (2011 batch); B4, complete acetolysed pollen grain at SEM at 5000× magnification (2012 batch); B5, detail of the acetolysed exine at SEM at 20 000× magnification (2012 batch); B6, detail of the acetolysed exine at SEM at 30 000× magnification (2012 batch). Red arrows highlight some examples of branched spinules.

Pollen of Triticum boeoticum subsp. thaoudar: C1, complete non-acetolysed pollen grain at scanning electron microscopy (SEM) at 5000× magnification (2009 batch) (sample INA-53); C2, detail of the non-acetolysed exine at SEM at 20 000× magnification (2009 batch) (sample INA-58); C3, detail of the acetolysed exine at phase-contrast microscopy (2011 batch) (sample INA-45); C4, complete acetolysed pollen grain at SEM at 5000× magnification (2011 batch) (sample INA-47); C5, detail of the acetolysed exine at SEM at 20 000× magnification (2011 batch) (sample INA-54); C6, detail of the acetolysed exine at SEM at 30 000× magnification (2012 batch) (sample INA-45). Pollen of Triticum boeoticum subsp. aegilopoides (sample INA-40): D1, complete non-acetolysed pollen grain at SEM at 5000× magnification (2009 batch); D2, detail of the non-acetolysed exine at SEM at 20 000× magnification (2009 batch); D3, detail of the acetolysed exine at phase-contrast microscopy (2011 batch); D4, complete acetolysed pollen grain at SEM at 5000× magnification (2011 batch); D5, detail of the acetolysed exine at SEM at 20 000× magnification (2011 batch); D6, detail of the acetolysed exine at SEM at 30 000× magnification (2012 batch). Red arrows highlight some examples of branched spinules.