Deposition of suberin in roots of soybean induced by excess boron

Seedlings of soybean (Glycine max cv. Enrei) were treated with 0.01, 0.05, and 5 mM boron (B) as boric acid. Depression of the growth, increase of the activities of phenylalanine ammonia-lyase and syringaldazine peroxidase, increase of lignin and wall bound phenols resulted from treatment with 5 mM B, compared to the treatments containing 0.05 and 0.01 mM B. Extensive suberization of cells was exclusively observed in root tips of seedlings exposed to 5 mM B. These phenomena may be specific responses of the plant to the stress of excess B and probably are relevant to the strategy of the plant, by which the radial transport of water and B toward conductive tissues is hindered.