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 Physio l,, 115, 901-916) requires high levels of boron (B) for normal growth, We a nalyzed 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 we re severely impaired by B deficiency in young rosette leaves. Such defects in growth were correlated with the reduced contents of B in leaves. These d efects were not observed when a sufficient amount of B was supplied. Uptake experiments with B-10-enriched tracer B demonstrated that B taken up throu gh roots was preferentially transported to young leaves compared to old lea ves in the wild-type plants under a low B supply. Such a preferential trans port to young leaves was not evident in the mutant plants. In conclusion, o ur data demonstrated that in A. thaliana plants B is preferentially transpo rted to young organs under a low B supply and that this transport process i s controlled at least in part by the BOR1 gene.