We have known that B is a required element for plants since 1926, but only one function for B in plant has been revealed. We now know that B acts in the cell wall, but data suggest that there are more functions of B. Boron deficiency also increases K efflux, an indication that B is required for cell membrane integrity. The goal of this research was to determine if there are other functions for B in the plant, possibly in the cell membrane, and characterize these functions.; One way to measure membrane integrity is to evaluate processes that occur at the membrane, such as maintenance of nutrient concentrations. When squash were grown in hydroponics and B was removed, water-extractable Mg and K concentrations in the root tips decreased rapidly compared to roots exposed to sufficient B. Decreases in K concentrations caused by B deficiency have been reported previously, but this is the first report that B deficiency quickly decreases Mg concentrations.; Decreased Mg concentrations due to B deficiency appear to occur independently of stunted root growth. Also, it appears that B deficiency causes a decrease in Mg uptake, although other possibilities have not been dismissed. It is difficult to make conclusions since no Mg uptake system has been identified in plants.; Boron deficiency causes similar symptoms as Al toxicity such as stunted root growth, root swelling, and decreased Mg uptake. Therefore, plants were exposed to B deficiency and Al toxicity and the water-extractable Mg concentrations in root tips were measured. Both B deficiency and Al toxicity decreased Mg concentrations, but the combination of the two stresses had an additive effect. This finding suggests Al toxicity and B deficiency decrease Mg concentrations in different ways.; When excessive Mg was applied to B-deficient roots, root growth was not restored, but root tip Mg and K concentrations were. These results indicate that B directly functions in Mg uptake, and that a loss of membrane integrity and decreased K concentrations are secondary symptoms caused by decreased Mg concentrations. Therefore, B may function in the cell membrane by maintaining Mg concentrations. Many questions remain, and other functions for B in plants remain possible and even likely.
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