Absorption and mobility of foliar-applied boron in soybean as affected by plant boron status and application as a polyol complex
In the present study (i) the impact of plant Boron (B) status on foliar B absorption and (ii) the effect of B complexation with polyols (sorbitol or mannitol) on B absorption and translocation was investigated. Soybean ( Glycine max (L.) Meer.) plants grown in nutrient solution containing 0 µM, 10 µM, 30 µM or 100 µM B labelled boric acid (BA) were treated with 50 m MB labelled BA applied to the basal parts of two leaflets of one leaf, either pure or in combination with 500 m M sorbitol or mannitol. After one week, B concentrations in different plant parts were determined. In B deficient leaves (0 µM B), B absorption was significantly lower than in all other treatments (9.7% of the applied dose vs. 26%-32%). The application of BA in combination with polyols increased absorption by 18-25% as compared to pure BA. The absolute amount of applied B moving out of the application zone was lowest in plants with 0 µM B supply (1.1% of the applied dose) and highest in those grown in 100 µM B (2.8%). The presence of sorbitol significantly decreased the share of mobile B in relation to the amount absorbed. The results suggest that B deficiency reduces the permeability of the leaf surface for BA. The addition of polyols may increase B absorption, but did not improve B distribution within the plant, which was even hindered when applied a sorbitol complex.

