Preferential translocation of boron to young leaves in Arabidopsis thaliana Regulated by the BOR1 Gene

A mutant of Arabidopsis thaliana, bor1-1 (Noguchi et al. 1997: Plant Physiol., 115, 901–916) requires high levels of boron (B) for normal growth. We analyzed the B-deficiency symptoms of bor1-1 mutant plants in detail. A low B supply retarded the growth of the mutant plants more evidently in leaves than in roots. In particular, cell expansion and formation of air spaces were severely impaired by B deficiency in young rosette leaves. Such defects in growth were correlated with the reduced contents of B in leaves. These defects were not observed when a sufficient amount of B was supplied. Uptake experiments with ¹⁰B-enriched tracer B demonstrated that B taken up through roots was preferentially transported to young leaves compared to old leaves in the wild-type plants under a low B supply. Such a preferential transport to young leaves was not evident in the mutant plants. In conclusion, our data demonstrated that in A. thaliana plants B is preferentially transported to young organs under a low B supply and that this transport process is controlled at least in part by the BOR1 gene.