Barriers to uptake of excess boron exist between xylem and the outer layers of whole roots of barley Yariety, Sahara 3771

摘要

Boron (B) uptake by whole root and xylem was studied in two barley varieties (Sahara 3771 and Clipper) known to differ in B tolerance. A significantly lower rate of B uptake and lower B concentrations in both the whole root and xylem sap were observed in Sahara 3771 compared to B-toxicity-sensitive Clipper. After plants were transferred to the high B treatment, the B concentration of the xylem sap in Sahara 3771 was significantly lower than the B concentration in the whole fresh root, indicating the presence of a barrier to B uptake into the xylem. In contrast, whole root B concentrations in Clipper were lower than xylem B concentration and no barrier was observed. It is suggested that barriers to B uptake exist not only at the whole root level but most likely also at the sites of xylem loading restricting long-distant B transport to the shoot.