The Role of Boron in Plant Growth: IV. INTERRELATIONSHIPS BETWEEN BORON AND INDOL-3YL-ACETIC ACID IN THE METABOLISM OF BEAN RADICLES

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Abstract
The hypothesis that boron deficiency is equivalent to a state of IAA toxicity was explored. Bioassays showed that extracts of substances similar to IAA taken from boron-deficient roots were significantly more inhibitory to the growth of bean-root segments than those from normal roots. Supplied IAA and boron deficiency together restricted root growth to a greater extent than either deficiency or IAA treatment separately. Roots were found to recover more quickly from the inhibitory effects of supplied IAA if boron was present at high (0.5 ppm) rather than low (0.01 ppm) concentrations. Experiments with 14C-labelled IAA showed that deficient roots absorbed 14C more slowly than boron-fed roots and there was also a lower rate of decarboxylation in the deficient tissue. Consideration of the published evidence showed that many of the effects of boron deficiency could follow from an upset in IAA metabolism. It is suggested that boron-deficient tissue suffers from excess auxin either because the element is necessary for some growth process, such as cell wall formation or nucleic acid synthesis, which, when impaired, results in the accumulation of auxin, or because the IAA-oxidation system is affected by phenolic inhibitors which boron normally inactivates by complex formation.

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