Abstract
Boron is an essential element for plant growth with a very narrow window between deficiency and toxicity. Arabidopsis BOR1 is a boron exporter for xylem loading. Accumulation of BOR1 protein is regulated by boron availability at translational/post-translational levels. In this study, localization of BOR1-GFP in root tip cells of 35S:BOR1-GFP transgenic plants were followed after change in the medium B concentration. Under boron limitation, BOR1-GFP localized mainly to plasma membrane. After addition of a high concentration of boron, BOR1-GFP moved into dot-like structures in the cytoplasm prior to disappearance. Studies using various inhibitors suggested BOR1 transport via endosome and degradation in vacuole. These results suggest that endocytosis and degradation of BOR1 is regulated by B availability, to avoid accumulation of toxic levels of B in shoots under high B supply, while protecting the shoot from B deficiency under B limitation.
