The Role of Boron in the Translocation of Sucrose

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Abstract
An hypothesis is presented to account for one essential role of B in plants. It is postulated that borate ions react with sugar molecules to form sugar-borate complexes (ionizable) which move through cellular membranes more readily than non-borated, non-ionized, sugar molecules. As measured with a Warburg apparatus, the respiration of lima bean and pea root tips was increased 50 to 85% when 5 ppm. of B were added to a solution of sucrose used as substrate. The increased respiration was interpreted as resulting from an increase in the movement of sucrose, or its hydrolytic products, to the respiring cells. In other expts., when a single leaf of a tomato plant was immersed in C14 tagged sucrose soln. containing 10 ppm. of B, the stem tips of such plants had an average of 550% more radioactivity than when the solution contained no B. In the absence of B the radioactivity was limited to the stem sections adjacent to the immersed leaf. Similar results were obtained with snap beans. These data are interpreted as evidence for the proposed hypothesis that sugars do not move readily through cellular membranes unless they are borated and hence ionized. It is submitted, therefore, that B deficiency symptoms are, in reality, symptoms of sugar deficiency.

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