Boron Uptake by Excised Barley Roots

Abstract

At 2.degree. C, all B accumulated by excised roots (Hordeum vulgare L. cv. ''Herta'') remains in the free space; i.e., active uptake is nil at this temperatuure. Three component fractions of free space B were apparent, a surface contaminant film of B on blotted roots, water free space B, and B reversibly bound in the cell walls. A stoichiometric release of H+ from the roots in the presence of B indicated that B was bound by borate complexes with polysaccharides in the cell walls. Polysaccharide-borate complexes are much less stable than those of monosaccharides, and the bound B fraction could be readily removed by rinsing the roots in the presence of a monomeric polyol possessing the necessary cis-diol configuration. Cell wall material separated from excised barley roots had a B binding capacity 66% greater than that of intact roots. A 30-min rinse in distilled H2O or 0.5 mM CaSO4 was required to remove all cell wall-bound B from the roots after a 30-min uptake period. Thus, although B in the contaminant surface film and the water free space is rinsed from the roots within 10 min, a 30-min rinse is essential if all reversibly accumulated B is to be removed from the free space.