Isolation of soluble boron complexes and their determination together withfree boric acid in higher plants

Isolation of soluble boron complexes and their quantitative determination t ogether with free boric acid in higher plants was carried out by gel permea tion chromatography in the liquid compartment of plant leaves and roots. Th e described method is suitable not only for the isolation of B complexes fr om plant cell sap, but also allows for their quantitative determination tog ether with free boric acid, which is possible for samples with a B concentr ation of at least 15 mu mol L-1 (Table 2). This gel permeation chromatograp hy method therefore complements methods that allow characterization, but no t quantitative determination of B complexes in plant samples. Soluble B complexes have been isolated from sunflower (Helianthus annuus L. ) grown with a marginal to toxic B supply and curly kale (Brassica oleracea L.). In sunflower root symplasm there was only a small concentration of B complexes that was not dependent on variations in B supply from the margina l to the toxic level. The resulting large variations in total symplasmic B were therefore only reflected in the concentrations of free boric acid. In contrast, the concentration of B complexes in sunflower leaf symplasm was a bout 50-fold larger than in the root symplasm and made up 31% of the total symplasmic B. In curly kale leaves even 59 % of the total symplasmic B was present as B complexes. Further experiments are necessary to characterize t he B complexes in sunflower and curly kale to investigate their physiologic al role in plant metabolism.