A major β-amylase expressed in radish taproots

Radish (Raphanus sativus L.) taproots display high amylolytic activity. Amylase zymograms using gels containing soluble starch and β-limit dextrin have indicated that β-amylase is a major amylolytic enzyme. We purified β-amylase with anion-exchange chromatography followed by glycogen precipitation. From the deduced amino acid sequences, a cDNA clone designated Raphanus sativus β-amylase 1 (RsBAMY1) was isolated. RsBAMY1 closely resembled Arabidopsis thaliana major β-amylase (At4g15210). Immunoblot analyses performed using an anti-RsBAMY1 antibody that was raised against a peptide sequence found in RsBAMY1 showed that the RsBAMY1 protein accumulated in the taproot. In addition, the transcriptional level and the protein accumulation of RsBAMY1 were enhanced during the taproot growth. These results suggest that RsBAMY1 is a major starch-digestive enzyme in the radish taproot.