Adventitious root growth inhibition in boron-deficient or aluminum-stressed sunflower seedlings

Sunflower(Helianthus annuus L.) seedings were de-rooted and grown in nutrient solutions providing either deficient or sufficient boron supply and supplemented with aluminum. Increasing concentrations of aluminum in the nutrient medium caused progressive inhibition of root growth and a parallel increase in proline level of roots. Elevated boron levels improved root growth under toxic aluminum conditions and produced higher proline contents. Exogenous ascorbate improved adventitions root growth in plants supplied with insufficient boron and aluminum. These findings suggest that root growth inhibition resulting from either boron deficiency or aluminum toxicity may be a result of impaired ascorbate metabolism.