Boron in Relation to Membrane Function in Higher Plants

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Abstract
The capacity for absorption of phosphate was shown to be reduced in Zea mays and Vicia faba suffering from boron deficiency; addition of 10−5 M boron rapidly restored this capacity. Root tips of normal plants also responded to the addition of boron during a short pretreatment period prior to the determination of phosphate absorption. Comparable effects of boron on the absorption of chloride and rubidium ions were also demonstrated in Zea mays. Specific inhibition of ion uptake by auxins may be relevant to the mechanism of the impaired ion transport seen during boron deficiency. The KCl-stimulated adenosine triphosphatase (ATPase) of the roots of Zea mays was also studied, with a view to examining the effect of boron deficiency on the activity of the enzyme. Boron-deficient roots had a reduced ATPase activity which could be rapidly restored by the addition of 10−4 M H3BO3 1 h before extraction of the enzyme. The results suggest that the activity of specific membrane components can be directly influenced by boron. Possible mechanisms whereby this control is exercised include direct interaction of boron with polyhydroxy components of the membrane and the elevation of endogenous levels of auxins. The evidence presented strongly supports the view that boron plays an essential role in the regulation of the functions of higher plant membranes and that the ATPase is a possible component of the transplant process.