The experiments was carried out with extraneous hormones treating su gar beet and analyzed changes of amylase activity and isoenzymes of it to study mechanism of bolting and bolting reversing of sugar beet in the first year. The results were follows: among extraneous hormones, G-ABA made sugar beet which is biennial plant bolting at the first year, during the bolting amylase activities increased after twelve days by treating, then the activity decreased which is li ke those plants bolting in the first growt...