BORON UPTAKE BY SUNFLOWER, SQUASH AND CULTURED TOBACCO CELLS

Boron uptake was studied in sunflower (Helianthus annuus cv. Ha301), squash (Cucurbita pepo cv. Early prolific straight neck) and cultured tobacco (Nicotiana tobacum L. cv. TXD Monsanto cell line) cells with the use of stable B isotopes and inductively coupled plasma mass spectrometry. Boron uptake increased linearly with increasing B concentrations in the uptake medium, did not exhibit multiphasic kinetics and was not saturable over a wide concentration range. The addition of respiratory inhibitors to the uptake solution or exposure to low (2 degrees C) or high (42 degrees C) temperatures did not inhibit B uptake. The majority of the B within the plants, including recently absorbed B, was present in a nonexchangeable form and could not be removed by repeated rinsing with deionized water or exchange with B isotope. These results demonstrate that in these species B uptake is a passive, nonmetabolic process and that the formation of nonexchangeable B-complexes within the cytoplasm and cell wall is a key factor in determining the uptake of B by plants.