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Symbol: B. A metalloid element, atomic number 5, atomic weight 10.81, found in very low concentrations in plant tissues. Its role is uncertain though boron deficiency quickly results in changes in cell membrane function and in cell extension. Various plant diseases, e.g. heart rot of beets and alfalfa yellows, have been attributed to boron deficiency. It has been suggested that a boron-sugar complex is involved in the movement of substrates through the phloem, though this idea is now largely rejected. Pollen germination and pollen tube growth are both greatly enhanced by addition of borate to the growth medium. Boron has been implicated in the uptake of calcium and appears necessary for the proper development of apical meristems.
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