BORON NUTRITION OF CULTURED TOBACCO BY-2 CELLS .2. CHARACTERIZATION OF THE BORON-POLYSACCHARIDE COMPLEX

In cultured tobacco BY-2 cells, more than 90% of the cellular boron (B ) occurs in the cell wall and a negligible amount of B is detected in the membrane fraction. Nearly 80% of the cell wall B binds to rhamnoga lacturonan II (RG-II) to form a borate-dimeric RG-II complex. Monomeri c RG-II is not detected in the cell wall, but it is detected in the ex tracellular polysaccharides, The complex is reconstituted spontaneousl y in vitro simply by mixing monomeric RG-II and boric acid at pH 4. Ge rmanic acid, which partially substitutes for B in the growth of the B- deprived plants, also induces dimerization of RG-II, These results sug gests that B may fulfill its essential function as forming the B-RG-II complex in cell walls.