BORON DISTRIBUTION IN PARENCHYMA CELLS OF CLOVER LEAVES

Using the two stable isotopes of boron, B-10 and B-11, and the nuclear reaction B-10(n,alpha)Li-7, we have imaged the distribution of boron in leaf parenchyma cells of approximately 3-weeks old clover plants, u sing the method of neutron capture radiography. When the plantlets wer e fed with a nutrient solution containing 16 muM boric acid, the boron concentrations (mmol kg-1 fresh weight) were found to be 7.64 in the cell wall, 0.35 in the cytoplasm, and practically zero in the vacuole. Moreover by using plantlets fed with either B-11-enriched or B-10-enr iched boric acid, and considering the boron isotopic abundances in the subcellular compartments, it was shown that the cytoplasmic boron ori ginated in almost equal amounts from the seed reserves and from the ab sorption from the nutrient medium via the roots, whereas in the cell w alls only 1/4 of the total boron came from the seed reserves and 3/4 f rom absorption from the nutrient medium. This is consistent with a non -negligible apoplastic transport of boron in these plants.