Abstract
Boron deficiency in sunflower resulted in abnormal root morphology. Six hours after transfer to boron-deficient nutrient medium, root elongation was inhibited; numerous ultrastructural symptoms, such as altered cell wall deposition and perturbations in the plasma and mitochondrial membranes, were evident. These early responses to boron deficiency are similar to those caused by exogenously supplied optimal indoleacetic acid (IAA). Using a sensitive radioimmunoassay for IAA, we found no significant difference in free IAA between boron-deficient and control root tips after treatment for 6, 24, and 72 h. The growth rate of boron-starved root tips was less than control root tips, but both showed similar levels of endogenous free IAA. Thus, in sunflower, early boron deficiency symptoms cannot be correlated with elevated levels of endogenous IAA.
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