The Biological Activity of Organoboron Compounds in the Promotion of Root Growth

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Abstract
The growth of the bean (Vicia faba var. minor) radicle in nutrient solution requires the presence of borate. Optimum extension growth, over 41 h, was obtained in the presence of 0.5 μM boric acid. This requirement of borate for root growth could also be satisfied by PhB(OH)2, 2-OCH3PhB(OH)2, and 4-OCH3PhB(OH)2. These three compounds also complex in vitro with catechol-3, 5-disulphonic acid. NaPh4B and 2, 6-OCH3)2PhB(OH)2 did not form such complexes in vitro, but were biologically active as sources of boron for radicle growth. This activity of NaPh4B was absent if roots were grown in solutions which were changed every 8 h. The activity of both NaPh4B and 2,6-(OCH3)2PhB(OH)2 was increased by using stock aqueous solutions which were not freshly prepared.The results are considered to provide support for the hypothesis that the activity of borate, as an essential plant nutrient, depends upon its ability to form a biologically active complex with an in vivo cis-diol compound.

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