Boron delays dehydration and stimulates root growth in Eucalyptus urophylla (Blake, S.T.) under osmotic stress

Abstract

Water and nutritional restrictions are limiting factors for the growth of Eucalyptus trees in tropical climates. In the dry season, boron (B) uptake is severely affected. The objectives of this study were to evaluate the phloem mobility of B and whether its deficiency can increase plant sensitivity to osmotic stress. It was also tested to what extent foliar application of B could mitigate the negative effects of drought under low B supply. Seedlings of a drought tolerant Eucalyptus urophylla (Blake, S. T.) clone were grown in nutrient solution, subjected to low availability of B for 25 days, and then submitted to a progressive osmotic stress. After imposition of osmotic stress, B was applied to young or mature leaves. B applications, mainly to mature leaf, stimulated root growth and delayed dehydration under osmotic stress and led to an increased B translocation and carbon isotopic composition. The expression of B transporters and pectin metabolism genes were also increased in water-stressed plants supplied with B by foliar application. B deficiency led to increased plant dehydration and decreased root growth under osmotic stress. The application of B to mature leaf of water-stressed plants proved effective in mitigating the negative effects of water deficit in root growth.