Cultured cells of tobacco (Nicotiana tabacum L.) BY-2 which could propagate at the same rate as the parent cells (1 mg B liter(-1)) under a lower level of boron (0.01 mg B liter(-1)) were obtained. The selected cells had swollen cell walls. In the parent cells, all the RG-II occurred as a B-RG-II complex, however, two-thirds of the RG-II occurred in a monomeric form in the selected cells.

A polyclonal antibody against a borate-RG-II complex is raised in rabbits. The antibody recognized RG-II exclusively in cell wall polysaccharides. Immunochemical studies demonstrated that the epitope is ubiquitous in cell walls of all the cells in radish and rice roots, cultured tobacco cells, red clover root nodules, and lily growing pollen tubes. The label was denser in proximal to plasma membrane, and not detected in middle lamella, suggesting that borate may cross-link newly secreted pectic polysaccharides at the membrane-cell wall interface.

A polyclonal antibody toward the borate-rhamnogalacturonan-II (RG-II) complex was raised in rabbits. The antibody recognizes RG-II exclusively in cell walls. Immunocytochemical studies reveal that the epitope is ubiquitous in cell walls of all the cells in radish (Rhaphanus sativus) roots. The label was denser proximal to the plasma membrane and was not detected in the middle lamella. These results suggests that the borate bridge between RG-II chains is important for the network formation of newly produced pectic polysaccharides, and that the bridge may not be involved in cell to cell adhesion.

A boron-polysaccharide complex was isolated and purified from germinating lily (Lilium longiflorum) pollen grains. From an analysis of sugar constituents, the sugar component of the complex is revealed to be rhamnogalacturonan II (RG-II). Immunocytochemistry using an antibody against the boron-RG-II complex of radish root cell walls demonstrated that the epitope is localized in the cell walls of elongating pollen tubes.