Developmental Regulation of Mannan, Arabinogalactan‐Protein, and Pectic Epitopes in Pistils of Vicia faba (Faba Bean)

Cell walls of the stigma and style are important zones for cell-cell recognition, nutrition, guidance, and protection of the pollen tube along the transmitting tract. The objective of this study was to investigate the modulation of selected cell wall epitopes during pistil development in the crop species Vicia faba L. (faba bean). An immunocytochemical investigation of pistil development was performed using a panel of four anti– cell wall/plasma membrane antibodies at both light and electron microscope levels during the 4 days leading up to anthesis. The selected antibodies recognized mannan-containing polysaccharides (antimannan antisera), b-1,4-galactan (LM5), a-1,5-L-arabinan (LM6), and arabinogalactan/arabinogalactan-protein (AG/AGP) epitopes, with GlcpUA-b-1,!3-D-Gal pUA-a-1,!2-L-Rha trisaccharide motifs (JIM13). Mannan accumulation was shown to be associated with the formation and maturation of sclerenchyma cells and xylem elements. The b-1,4-galactan and a-1,5-L-arabinan epitopes were highly expressed in the walls of parenchyma and epidermis in a developmentally regulated manner. AG/AGP epitopes were particularly abundant in the stigma and cells lining the stylar canal, together with the a-1,5-L-arabinan epitope recognized by LM6. These data suggest an association of AGs/AGPs with pollen tube growth, of mannan with strengthening and stiffening the pistil, and of b-1,4-galactan and a-1,5-L-arabinan components with tissue flexibility within the pistil.